The increasing number of threads inside the cores of a multicore processor, and competitive access to the
shared cache memory, become the main reasons for an increased number of competitive cache misses and
performance decline. Inevitably, the development of modern processor architectures leads to an increased
number of cache misses. In this paper, we make an attempt to implement a technique for decreasing the
number of competitive cache misses in the first level of cache memory. This technique enables competitive
access to the entire cache memory when there is a hit – but, if there are cache misses, memory data (by using replacement techniques) is put in a virtual part given to threads, so that competitive cache misses are avoided. By using a simulator tool, the results show a decrease in the number of cache misses and performance increase for up to 15%. The conclusion that comes out of this research is that cache misses are a real challenge for future processor designers, in order to hide memory latency.
This document evaluates the performance of four memory consistency models (sequential consistency, processor consistency, weak consistency, and release consistency) for shared-memory multiprocessors using simulation studies of three applications (MP3D, LU, and PTHOR). The results show that sequential consistency performs significantly worse than the other models. Surprisingly, processor consistency performs almost as well as release consistency and better than weak consistency for one application, indicating that allowing reads to bypass pending writes provides more benefit than allowing writes to pipeline.
PARALLEL ARCHITECTURE AND COMPUTING - SHORT NOTESsuthi
1. Parallel computing involves dividing large problems into smaller subproblems that can be solved simultaneously to reduce processing time.
2. There are two main reasons for using parallel computing: to save time and solve larger problems.
3. Parallel architectures can be classified based on how instructions and data are distributed, the coupling between processing elements, how memory is accessed, and the granularity of work.
Cache memory is a fast memory located between the CPU and main memory that stores frequently accessed instructions and data. It improves system performance by reducing memory access time. Cache is organized into multiple levels - L1 cache is closest to the CPU, L2 cache is next, and some CPUs have an L3 cache. (Level 1, 2, 3 caches refer to their proximity to the CPU.) Cache memory uses SRAM instead of DRAM for faster access. It is organized into rows containing a data block, tag, and flag bits. Optimization techniques for cache include improving data locality through code transformations and maintaining coherence across cache levels.
This document presents benchmarks to analyze the memory subsystem performance of multicore processors from AMD and Intel. The benchmarks measure latency and bandwidth for different cache coherence states and locations in the memory hierarchy. Testing was done on dual-socket systems using AMD Opteron 2300 (Shanghai) and Intel Xeon 5500 (Nehalem-EP) quad-core processors. Results show significant performance differences driven by each processor's distinct cache architecture and coherence protocol implementations.
The processor-memory bandwidth in modern generation
processors is the important bottleneck due to a number of
processor cores dealing it through with the same bus/ processor-
memory interface. Caches take a significant amount
of energy in current microprocessors. To design an energyefficient
microprocessor, it is important to optimize cache
energy economic consumption. Powerful utilization of this
resource is consequently an important view of memory hierarchy
design of multi core processors. This is presently an
important field of research on a large number of research
issues that have suggested a number of techniques to figure
out the problem. The better contribution of this theme is the
assessment of effectiveness of some of the proficiencies that
were enforced in recent chip multiprocessors. Cache optimization
techniques that were named for single core processors
but have not been implemented in multi core processors
are as well tested to forecast their effectiveness.
1. In multiprocessor systems, failure of one processor will not halt the system, but only slow it down by sharing the work of the failed processor among the other surviving processors. This ability to continue functioning is called graceful degradation.
2. System calls are required for user processes to access operating system services.
3. Solutions to the critical section problem must satisfy three requirements: mutual exclusion, progress, and bounded waiting. Mutual exclusion means only one process in the critical section at a time. Progress means waiting processes can enter if the section is empty. Bounded waiting means a limit on wait times.
Architecture and implementation issues of multi core processors and caching –...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
This document evaluates the performance of four memory consistency models (sequential consistency, processor consistency, weak consistency, and release consistency) for shared-memory multiprocessors using simulation studies of three applications (MP3D, LU, and PTHOR). The results show that sequential consistency performs significantly worse than the other models. Surprisingly, processor consistency performs almost as well as release consistency and better than weak consistency for one application, indicating that allowing reads to bypass pending writes provides more benefit than allowing writes to pipeline.
PARALLEL ARCHITECTURE AND COMPUTING - SHORT NOTESsuthi
1. Parallel computing involves dividing large problems into smaller subproblems that can be solved simultaneously to reduce processing time.
2. There are two main reasons for using parallel computing: to save time and solve larger problems.
3. Parallel architectures can be classified based on how instructions and data are distributed, the coupling between processing elements, how memory is accessed, and the granularity of work.
Cache memory is a fast memory located between the CPU and main memory that stores frequently accessed instructions and data. It improves system performance by reducing memory access time. Cache is organized into multiple levels - L1 cache is closest to the CPU, L2 cache is next, and some CPUs have an L3 cache. (Level 1, 2, 3 caches refer to their proximity to the CPU.) Cache memory uses SRAM instead of DRAM for faster access. It is organized into rows containing a data block, tag, and flag bits. Optimization techniques for cache include improving data locality through code transformations and maintaining coherence across cache levels.
This document presents benchmarks to analyze the memory subsystem performance of multicore processors from AMD and Intel. The benchmarks measure latency and bandwidth for different cache coherence states and locations in the memory hierarchy. Testing was done on dual-socket systems using AMD Opteron 2300 (Shanghai) and Intel Xeon 5500 (Nehalem-EP) quad-core processors. Results show significant performance differences driven by each processor's distinct cache architecture and coherence protocol implementations.
The processor-memory bandwidth in modern generation
processors is the important bottleneck due to a number of
processor cores dealing it through with the same bus/ processor-
memory interface. Caches take a significant amount
of energy in current microprocessors. To design an energyefficient
microprocessor, it is important to optimize cache
energy economic consumption. Powerful utilization of this
resource is consequently an important view of memory hierarchy
design of multi core processors. This is presently an
important field of research on a large number of research
issues that have suggested a number of techniques to figure
out the problem. The better contribution of this theme is the
assessment of effectiveness of some of the proficiencies that
were enforced in recent chip multiprocessors. Cache optimization
techniques that were named for single core processors
but have not been implemented in multi core processors
are as well tested to forecast their effectiveness.
1. In multiprocessor systems, failure of one processor will not halt the system, but only slow it down by sharing the work of the failed processor among the other surviving processors. This ability to continue functioning is called graceful degradation.
2. System calls are required for user processes to access operating system services.
3. Solutions to the critical section problem must satisfy three requirements: mutual exclusion, progress, and bounded waiting. Mutual exclusion means only one process in the critical section at a time. Progress means waiting processes can enter if the section is empty. Bounded waiting means a limit on wait times.
Architecture and implementation issues of multi core processors and caching –...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
This document summarizes a paper that proposes and evaluates the performance of a multithreaded architecture capable of exploiting both coarse-grained parallelism and fine-grained instruction-level parallelism. The architecture distributes processing across multiple processing elements connected by an interconnection network. Each processing element supports multiple concurrently executing threads by grouping instructions from different threads. The architecture introduces a distributed data structure cache to reduce network latency when accessing remote data. Simulation results indicate the architecture achieves high processor throughput and the data structure cache significantly reduces network latency.
Cache coherence is a technique used in multiprocessing systems to maintain consistency between caches and shared memory. When a processor modifies a variable in its cache that is also stored in another processor's cache, inconsistency arises. There are three main techniques to maintain cache coherence: snoopy-based protocols invalidate or update other caches when a write is observed; directory-based protocols use a directory to control access to shared data and update or invalidate caches; and snarfing-based protocols allow caches to watch addresses and data to update copies when writes are seen. Cache coherence aims to ensure data consistency across caches for shared resources.
Power minimization of systems using Performance Enhancement Guaranteed CachesIJTET Journal
Caches have long been an instrument for speeding memory access from microcontrollers to center based ASIC plans. For hard ongoing frameworks however stores are tricky because of most pessimistic scenario execution time estimation. As of late, an on-chip scratch cushion memory (SPM) to decrease the force and enhance execution. SPM does not productively reuse its space while execution. Here, an execution improvement ensured reserves (PEG-C) to improve the execution. It can likewise be utilized like a standard reserve to progressively store guidelines and information in view of their runtime access examples prompting attain to great execution. All the earlier plans have corruption of execution when contrasted with PEG-C. It has a superior answer for equalization time consistency and normal case execution
The document discusses non-uniform cache architectures (NUCA), cache coherence, and different implementations of directories in multicore systems. It describes NUCA designs that map data to banks based on distance from the controller to exploit non-uniform access times. Cache coherence is maintained using directory-based protocols that track copies of cache blocks. Directories can be implemented off-chip in DRAM or on-chip using duplicate tag stores or distributing the directory among cache banks. Examples of systems like SGI Origin2000 and Tilera Tile64 that use these techniques are also outlined.
MAC: A NOVEL SYSTEMATICALLY MULTILEVEL CACHE REPLACEMENT POLICY FOR PCM MEMORYcaijjournal
The rapid development of multi-core system and increase of data-intensive application in recent years call
for larger main memory. Traditional DRAM memory can increase its capacity by reducing the feature size
of storage cell. Now further scaling of DRAM faces great challenge, and the frequent refresh operations of
DRAM can bring a lot of energy consumption. As an emerging technology, Phase Change Memory (PCM)
is promising to be used as main memory. It draws wide attention due to the advantages of low power
consumption, high density and nonvolatility, while it incurs finite endurance and relatively long write
latency. To handle the problem of write, optimizing the cache replacement policy to protect dirty cache
block is an efficient way. In this paper, we construct a systematically multilevel structure, and based on it
propose a novel cache replacement policy called MAC. MAC can effectively reduce write traffic to PCM
memory with low hardware overhead. We conduct simulation experiments on GEM5 to evaluate the
performances of MAC and other related works. The results show that MAC performs best in reducing the
amount of writes (averagely 25.12%) without increasing the program execution time.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
This document discusses topics related to multicore programming and multithreading. It covers multicore programming models, multithreading models including many-to-many, many-to-one, and one-to-one. It also discusses thread libraries, implicit threading using OpenMP, and issues to consider for multithreaded programs such as fork/exec calls, signal handling, and cancellation.
In feltrinelli il testo Building Maintenance, redatto da Pietro Salomone ed edito dal Gruppo L'espresso S.p.A.
Un interessante panoramica nel mondo delle manutenzioni degli immobili sia pubblici che privati.
Que las actividades de innovación en el Perú han tenido impactos positivos muy importantes sobre los beneficiarios. Por ejemplo, se estima que la productividad de los trabajadores de las empresas manufactureras que realizan actividades de innovación es 30% mayor.
This document discusses the concepts of association and causation in epidemiology. It defines association as the occurrence of two variables more often than expected by chance. Association can be spurious, indirect, or direct (causal). Additional criteria for judging causality include temporal relationship, strength of association, dose-response relationship, replication of findings, biological plausibility, and consideration of alternative explanations. Establishing causality requires evaluating these criteria to determine if changes in the suspected cause are consistently linked to changes in the effect.
This document contains announcements for Penn Valley Church including information about helping the Grace Christian School financial aid fund, marching for life in Washington DC, online giving options, a new nonprofit helping single mothers, a Bible study on shepherding a child's heart, connecting with the Fellowship of Grace Brethren Churches, signing up for emergency alerts, helping in the nursery, updating the online church directory, fellowship breakfast locations and times, the Telford Campus women's prayer project, and intercessory prayer meetings.
Circulo Kaizen team Arre - Topic In Process (Operation Ratio)Samantha Neri
The document discusses the benefits of exercise for mental health. Regular physical activity can help reduce anxiety and depression and improve mood and cognitive functioning. Exercise causes chemical changes in the brain that may help protect against mental illness and improve symptoms.
a short (45 minutes) introduction to cerimonial magic, meme and mesmerism: una storia occulta della vittoria di Trump, by Tommaso Guariento @ The Empire Strikes Again (La Scuola Open Source) – www.lascuolaopensource.xyz
A keynote on aliens, nuclear waste, wicked problems, and the one big thing that unites everyone working in user experience: AMBIGUITY.
See a video and the full transcript of this keynote at http://www.jonathoncolman.org/2015/05/21/wicked-ambiguity/
How do you solve the world’s hardest problems? And how do you respond if they’re unsolvable? As user experience professionals, we're focused on people who live and work in the here and now. We dive into research, define the problem, break down silos, and build value by focusing on intent.
But how does our UX work change when a project lasts not for one year, or even 10 years, but for 10,000 years or more? Enter the “Wicked Problem,” or situations with so much ambiguity, complexity, and interdependencies that—by definition—they can’t be solved.
Using real-world examples from NASA’s Voyager program, the Yucca Mountain Nuclear Waste Repository, and other long-term UX efforts, we’ll talk about the challenges of creating solutions for people whom we’ll never know in our lifetimes. The ways we grapple with ambiguity give us a new perspective on our work and on what it means to build experiences that last.
Originally presented as the opening keynote for the 2014 Society for Technical Communication Summit in Phoenix, Arizona. Redeveloped as the opening keynote for the 2015 Confab Central conference and presented on May 21, 2015 in Minneapolis, Minnesota.
The growing rate of technology improvements has caused dramatic advances in processor performances,
causing significant speed-up of processor working frequency and increased amount of instructions which
can be processed in parallel. The given development of processor's technology has brought performance
improvements in computer systems, but not for all the types of applications. The reason for this resides in
the well known Von-Neumann bottleneck problem which occurs during the communication between the
processor and the main memory into a standard processor-centric system. This problem has been reviewed
by many scientists, which proposed different approaches for improving the memory bandwidth and latency.
This paper provides a brief review of these techniques and also gives a deep analysis of various memory-
centric systems that implement different approaches of merging or placing the memory near to the
processing elements. Within this analysis we discuss the advantages, disadvantages and the application
(purpose) of several well-known memory-centric systems.
The growing rate of technology improvements has caused dramatic advances in processor performances,
causing significant speed-up of processor working frequency and increased amount of instructions which
can be processed in parallel. The given development of processor's technology has brought performance
improvements in computer systems, but not for all the types of applications. The reason for this resides in
the well known Von-Neumann bottleneck problem which occurs during the communication between the
processor and the main memory into a standard processor-centric system. This problem has been reviewed
by many scientists, which proposed different approaches for improving the memory bandwidth and latency.
This paper provides a brief review of these techniques and also gives a deep analysis of various memory-
centric systems that implement different approaches of merging or placing the memory near to the
processing elements. Within this analysis we discuss the advantages, disadvantages and the application
(purpose) of several well-known memory-centric systems.
The growing rate of technology improvements has caused dramatic advances in processor performances, causing significant speed-up of processor working frequency and increased amount of instructions which can be processed in parallel. The given development of processor's technology has brought performance improvements in computer systems, but not for all the types of applications. The reason for this resides in the well known Von-Neumann bottleneck problem which occurs during the communication between the processor and the main memory into a standard processor-centric system. This problem has been reviewed by many scientists, which proposed different approaches for improving the memory bandwidth and latency. This paper provides a brief review of these techniques and also gives a deep analysis of various memorycentric systems that implement different approaches of merging or placing the memory near to the processing elements. Within this analysis we discuss the advantages, disadvantages and the application (purpose) of several well-known memory-centric systems
151 A SURVEY OF DIFFERENT APPROACHES FOR OVERCOMING THE PROCESSOR-MEMORY BOTT...ijcsit
The growing rate of technology improvements has caused dramatic advances in processor performances, causing significant speed-up of processor working frequency and increased amount of instructions which can be processed in parallel. The given development of processor's technology has brought performance
improvements in computer systems, but not for all the types of applications. The reason for this resides in the well known Von-Neumann bottleneck problem which occurs during the communication between the processor and the main memory into a standard processor-centric system. This problem has been reviewed by many scientists, which proposed different approaches for improving the memory bandwidth and latency.
This paper provides a brief review of these techniques and also gives a deep analysis of various memorycentric
systems that implement different approaches of merging or placing the memory near to the processing elements. Within this analysis we discuss the advantages, disadvantages and the application (purpose) of several well-known memory-centric systems.
MULTI-CORE PROCESSORS: CONCEPTS AND IMPLEMENTATIONSijcsit
This research paper aims at comparing two multi-core processors machines, the Intel core i7-4960X
processor (Ivy Bridge E) and the AMD Phenom II X6. It starts by introducing a single-core processor machine to motivate the need for multi-core processors. Then, it explains the multi-core processor machine and the issues that rises in implementing them. It also provides a real life example machines such as
TILEPro64 and Epiphany-IV 64-core 28nm Microprocessor (E64G401). The methodology that was used in comparing the Intel core i7 and AMD phenom II processors starts by explaining how processors' performance are measured, then by listing the most important and relevant technical specification to the
comparison. After that, running the comparison by using different metrics such as power, the use of HyperThreading
technology, the operating frequency, the use of AES encryption and decryption, and the different characteristics of cache memory such as the size, classification, and its memory controller. Finally, reaching to a roughly decision about which one of them has a better over all performance.
This research paper aims at comparing two multi-core processors machines, the Intel core i7-4960X processor (Ivy Bridge E) and the AMD Phenom II X6. It starts by introducing a single-core processor machine to motivate the need for multi-core processors. Then, it explains the multi-core processor machine and the issues that rises in implementing them. It also provides a real life example machines such as TILEPro64 and Epiphany-IV 64-core 28nm Microprocessor (E64G401). The methodology that was used in comparing the Intel core i7 and AMD phenom II processors starts by explaining how processors' performance are measured, then by listing the most important and relevant technical specification to the comparison. After that, running the comparison by using different metrics such as power, the use of HyperThreading technology, the operating frequency, the use of AES encryption and decryption, and the different characteristics of cache memory such as the size, classification, and its memory controller. Finally, reaching to a roughly decision about which one of them has a better over all performance.
The document discusses parallel computing platforms and trends in microprocessor architectures that enable implicit parallelism. It covers topics like pipelining, superscalar execution, limitations of memory performance, and how caches can improve effective memory latency. The key points are:
1) Microprocessor clock speeds have increased dramatically but limitations remain regarding memory latency and bandwidth. Parallelism addresses performance bottlenecks in processors, memory, and communication.
2) Techniques like pipelining and superscalar execution exploit implicit parallelism by executing multiple instructions concurrently, but dependencies and branch prediction limit performance gains.
3) Memory latency is often the bottleneck, but caches can reduce effective latency through data reuse and temporal locality.
Dominant block guided optimal cache size estimation to maximize ipc of embedd...ijesajournal
Embedded system software is highly constrained from performance, memory footprint, energy consumption and implementing cost view point. It is always desirable to obtain better Instructions per Cycle (IPC). Instruction cache has major contribution in improving IPC. Cache memories are realized on the same chip where the processor is running. This considerably increases the system cost as well. Hence, it is required to maintain a trade-off between cache sizes and performance improvement offered. Determining the number of cache lines and size of cache line are important parameters for cache designing. The design space for cache is quite large. It is time taking to execute the given application with different cache sizes on an instruction set simulator (ISS) to figure out the optimal cache size. In this paper, a technique is proposed to identify a number of cache lines and cache line size for the L1 instruction cache that will offer best or nearly best IPC. Cache size is derived, at a higher abstraction level, from basic block analysis in the Low Level Virtual Machine (LLVM) environment. The cache size estimated from the LLVM environment is cross validated by simulating the set of benchmark applications with different cache sizes in SimpleScalar’s out-of-order simulator. The proposed method seems to be superior in terms of estimation accuracy and/or estimation time as compared to the existing methods for estimation of optimal cache size parameters (cache line size, number of cache lines).
This document summarizes a paper that proposes and evaluates the performance of a multithreaded architecture capable of exploiting both coarse-grained parallelism and fine-grained instruction-level parallelism. The architecture distributes processing across multiple processing elements connected by an interconnection network. Each processing element supports multiple concurrently executing threads by grouping instructions from different threads. The architecture introduces a distributed data structure cache to reduce network latency when accessing remote data. Simulation results indicate the architecture achieves high processor throughput and the data structure cache significantly reduces network latency.
Cache coherence is a technique used in multiprocessing systems to maintain consistency between caches and shared memory. When a processor modifies a variable in its cache that is also stored in another processor's cache, inconsistency arises. There are three main techniques to maintain cache coherence: snoopy-based protocols invalidate or update other caches when a write is observed; directory-based protocols use a directory to control access to shared data and update or invalidate caches; and snarfing-based protocols allow caches to watch addresses and data to update copies when writes are seen. Cache coherence aims to ensure data consistency across caches for shared resources.
Power minimization of systems using Performance Enhancement Guaranteed CachesIJTET Journal
Caches have long been an instrument for speeding memory access from microcontrollers to center based ASIC plans. For hard ongoing frameworks however stores are tricky because of most pessimistic scenario execution time estimation. As of late, an on-chip scratch cushion memory (SPM) to decrease the force and enhance execution. SPM does not productively reuse its space while execution. Here, an execution improvement ensured reserves (PEG-C) to improve the execution. It can likewise be utilized like a standard reserve to progressively store guidelines and information in view of their runtime access examples prompting attain to great execution. All the earlier plans have corruption of execution when contrasted with PEG-C. It has a superior answer for equalization time consistency and normal case execution
The document discusses non-uniform cache architectures (NUCA), cache coherence, and different implementations of directories in multicore systems. It describes NUCA designs that map data to banks based on distance from the controller to exploit non-uniform access times. Cache coherence is maintained using directory-based protocols that track copies of cache blocks. Directories can be implemented off-chip in DRAM or on-chip using duplicate tag stores or distributing the directory among cache banks. Examples of systems like SGI Origin2000 and Tilera Tile64 that use these techniques are also outlined.
MAC: A NOVEL SYSTEMATICALLY MULTILEVEL CACHE REPLACEMENT POLICY FOR PCM MEMORYcaijjournal
The rapid development of multi-core system and increase of data-intensive application in recent years call
for larger main memory. Traditional DRAM memory can increase its capacity by reducing the feature size
of storage cell. Now further scaling of DRAM faces great challenge, and the frequent refresh operations of
DRAM can bring a lot of energy consumption. As an emerging technology, Phase Change Memory (PCM)
is promising to be used as main memory. It draws wide attention due to the advantages of low power
consumption, high density and nonvolatility, while it incurs finite endurance and relatively long write
latency. To handle the problem of write, optimizing the cache replacement policy to protect dirty cache
block is an efficient way. In this paper, we construct a systematically multilevel structure, and based on it
propose a novel cache replacement policy called MAC. MAC can effectively reduce write traffic to PCM
memory with low hardware overhead. We conduct simulation experiments on GEM5 to evaluate the
performances of MAC and other related works. The results show that MAC performs best in reducing the
amount of writes (averagely 25.12%) without increasing the program execution time.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
This document discusses topics related to multicore programming and multithreading. It covers multicore programming models, multithreading models including many-to-many, many-to-one, and one-to-one. It also discusses thread libraries, implicit threading using OpenMP, and issues to consider for multithreaded programs such as fork/exec calls, signal handling, and cancellation.
In feltrinelli il testo Building Maintenance, redatto da Pietro Salomone ed edito dal Gruppo L'espresso S.p.A.
Un interessante panoramica nel mondo delle manutenzioni degli immobili sia pubblici che privati.
Que las actividades de innovación en el Perú han tenido impactos positivos muy importantes sobre los beneficiarios. Por ejemplo, se estima que la productividad de los trabajadores de las empresas manufactureras que realizan actividades de innovación es 30% mayor.
This document discusses the concepts of association and causation in epidemiology. It defines association as the occurrence of two variables more often than expected by chance. Association can be spurious, indirect, or direct (causal). Additional criteria for judging causality include temporal relationship, strength of association, dose-response relationship, replication of findings, biological plausibility, and consideration of alternative explanations. Establishing causality requires evaluating these criteria to determine if changes in the suspected cause are consistently linked to changes in the effect.
This document contains announcements for Penn Valley Church including information about helping the Grace Christian School financial aid fund, marching for life in Washington DC, online giving options, a new nonprofit helping single mothers, a Bible study on shepherding a child's heart, connecting with the Fellowship of Grace Brethren Churches, signing up for emergency alerts, helping in the nursery, updating the online church directory, fellowship breakfast locations and times, the Telford Campus women's prayer project, and intercessory prayer meetings.
Circulo Kaizen team Arre - Topic In Process (Operation Ratio)Samantha Neri
The document discusses the benefits of exercise for mental health. Regular physical activity can help reduce anxiety and depression and improve mood and cognitive functioning. Exercise causes chemical changes in the brain that may help protect against mental illness and improve symptoms.
a short (45 minutes) introduction to cerimonial magic, meme and mesmerism: una storia occulta della vittoria di Trump, by Tommaso Guariento @ The Empire Strikes Again (La Scuola Open Source) – www.lascuolaopensource.xyz
A keynote on aliens, nuclear waste, wicked problems, and the one big thing that unites everyone working in user experience: AMBIGUITY.
See a video and the full transcript of this keynote at http://www.jonathoncolman.org/2015/05/21/wicked-ambiguity/
How do you solve the world’s hardest problems? And how do you respond if they’re unsolvable? As user experience professionals, we're focused on people who live and work in the here and now. We dive into research, define the problem, break down silos, and build value by focusing on intent.
But how does our UX work change when a project lasts not for one year, or even 10 years, but for 10,000 years or more? Enter the “Wicked Problem,” or situations with so much ambiguity, complexity, and interdependencies that—by definition—they can’t be solved.
Using real-world examples from NASA’s Voyager program, the Yucca Mountain Nuclear Waste Repository, and other long-term UX efforts, we’ll talk about the challenges of creating solutions for people whom we’ll never know in our lifetimes. The ways we grapple with ambiguity give us a new perspective on our work and on what it means to build experiences that last.
Originally presented as the opening keynote for the 2014 Society for Technical Communication Summit in Phoenix, Arizona. Redeveloped as the opening keynote for the 2015 Confab Central conference and presented on May 21, 2015 in Minneapolis, Minnesota.
The growing rate of technology improvements has caused dramatic advances in processor performances,
causing significant speed-up of processor working frequency and increased amount of instructions which
can be processed in parallel. The given development of processor's technology has brought performance
improvements in computer systems, but not for all the types of applications. The reason for this resides in
the well known Von-Neumann bottleneck problem which occurs during the communication between the
processor and the main memory into a standard processor-centric system. This problem has been reviewed
by many scientists, which proposed different approaches for improving the memory bandwidth and latency.
This paper provides a brief review of these techniques and also gives a deep analysis of various memory-
centric systems that implement different approaches of merging or placing the memory near to the
processing elements. Within this analysis we discuss the advantages, disadvantages and the application
(purpose) of several well-known memory-centric systems.
The growing rate of technology improvements has caused dramatic advances in processor performances,
causing significant speed-up of processor working frequency and increased amount of instructions which
can be processed in parallel. The given development of processor's technology has brought performance
improvements in computer systems, but not for all the types of applications. The reason for this resides in
the well known Von-Neumann bottleneck problem which occurs during the communication between the
processor and the main memory into a standard processor-centric system. This problem has been reviewed
by many scientists, which proposed different approaches for improving the memory bandwidth and latency.
This paper provides a brief review of these techniques and also gives a deep analysis of various memory-
centric systems that implement different approaches of merging or placing the memory near to the
processing elements. Within this analysis we discuss the advantages, disadvantages and the application
(purpose) of several well-known memory-centric systems.
The growing rate of technology improvements has caused dramatic advances in processor performances, causing significant speed-up of processor working frequency and increased amount of instructions which can be processed in parallel. The given development of processor's technology has brought performance improvements in computer systems, but not for all the types of applications. The reason for this resides in the well known Von-Neumann bottleneck problem which occurs during the communication between the processor and the main memory into a standard processor-centric system. This problem has been reviewed by many scientists, which proposed different approaches for improving the memory bandwidth and latency. This paper provides a brief review of these techniques and also gives a deep analysis of various memorycentric systems that implement different approaches of merging or placing the memory near to the processing elements. Within this analysis we discuss the advantages, disadvantages and the application (purpose) of several well-known memory-centric systems
151 A SURVEY OF DIFFERENT APPROACHES FOR OVERCOMING THE PROCESSOR-MEMORY BOTT...ijcsit
The growing rate of technology improvements has caused dramatic advances in processor performances, causing significant speed-up of processor working frequency and increased amount of instructions which can be processed in parallel. The given development of processor's technology has brought performance
improvements in computer systems, but not for all the types of applications. The reason for this resides in the well known Von-Neumann bottleneck problem which occurs during the communication between the processor and the main memory into a standard processor-centric system. This problem has been reviewed by many scientists, which proposed different approaches for improving the memory bandwidth and latency.
This paper provides a brief review of these techniques and also gives a deep analysis of various memorycentric
systems that implement different approaches of merging or placing the memory near to the processing elements. Within this analysis we discuss the advantages, disadvantages and the application (purpose) of several well-known memory-centric systems.
MULTI-CORE PROCESSORS: CONCEPTS AND IMPLEMENTATIONSijcsit
This research paper aims at comparing two multi-core processors machines, the Intel core i7-4960X
processor (Ivy Bridge E) and the AMD Phenom II X6. It starts by introducing a single-core processor machine to motivate the need for multi-core processors. Then, it explains the multi-core processor machine and the issues that rises in implementing them. It also provides a real life example machines such as
TILEPro64 and Epiphany-IV 64-core 28nm Microprocessor (E64G401). The methodology that was used in comparing the Intel core i7 and AMD phenom II processors starts by explaining how processors' performance are measured, then by listing the most important and relevant technical specification to the
comparison. After that, running the comparison by using different metrics such as power, the use of HyperThreading
technology, the operating frequency, the use of AES encryption and decryption, and the different characteristics of cache memory such as the size, classification, and its memory controller. Finally, reaching to a roughly decision about which one of them has a better over all performance.
This research paper aims at comparing two multi-core processors machines, the Intel core i7-4960X processor (Ivy Bridge E) and the AMD Phenom II X6. It starts by introducing a single-core processor machine to motivate the need for multi-core processors. Then, it explains the multi-core processor machine and the issues that rises in implementing them. It also provides a real life example machines such as TILEPro64 and Epiphany-IV 64-core 28nm Microprocessor (E64G401). The methodology that was used in comparing the Intel core i7 and AMD phenom II processors starts by explaining how processors' performance are measured, then by listing the most important and relevant technical specification to the comparison. After that, running the comparison by using different metrics such as power, the use of HyperThreading technology, the operating frequency, the use of AES encryption and decryption, and the different characteristics of cache memory such as the size, classification, and its memory controller. Finally, reaching to a roughly decision about which one of them has a better over all performance.
The document discusses parallel computing platforms and trends in microprocessor architectures that enable implicit parallelism. It covers topics like pipelining, superscalar execution, limitations of memory performance, and how caches can improve effective memory latency. The key points are:
1) Microprocessor clock speeds have increased dramatically but limitations remain regarding memory latency and bandwidth. Parallelism addresses performance bottlenecks in processors, memory, and communication.
2) Techniques like pipelining and superscalar execution exploit implicit parallelism by executing multiple instructions concurrently, but dependencies and branch prediction limit performance gains.
3) Memory latency is often the bottleneck, but caches can reduce effective latency through data reuse and temporal locality.
Dominant block guided optimal cache size estimation to maximize ipc of embedd...ijesajournal
Embedded system software is highly constrained from performance, memory footprint, energy consumption and implementing cost view point. It is always desirable to obtain better Instructions per Cycle (IPC). Instruction cache has major contribution in improving IPC. Cache memories are realized on the same chip where the processor is running. This considerably increases the system cost as well. Hence, it is required to maintain a trade-off between cache sizes and performance improvement offered. Determining the number of cache lines and size of cache line are important parameters for cache designing. The design space for cache is quite large. It is time taking to execute the given application with different cache sizes on an instruction set simulator (ISS) to figure out the optimal cache size. In this paper, a technique is proposed to identify a number of cache lines and cache line size for the L1 instruction cache that will offer best or nearly best IPC. Cache size is derived, at a higher abstraction level, from basic block analysis in the Low Level Virtual Machine (LLVM) environment. The cache size estimated from the LLVM environment is cross validated by simulating the set of benchmark applications with different cache sizes in SimpleScalar’s out-of-order simulator. The proposed method seems to be superior in terms of estimation accuracy and/or estimation time as compared to the existing methods for estimation of optimal cache size parameters (cache line size, number of cache lines).
Dominant block guided optimal cache size estimation to maximize ipc of embedd...ijesajournal
Embedded system software is highly constrained from performance, memory footprint, energy consumption
and implementing cost view point. It is always desirable to obtain better Instructions per Cycle (IPC).
Instruction cache has major contribu
tion in improving IPC. Cache memories are realized on the same chip
where the processor is running. This considerably increases the system cost as well. Hence, it is required to
maintain a trade
-
off between cache sizes and performance improvement offered.
Determining the number
of cache lines and size of cache line are important parameters for cache designing. The design space for
cache is quite large. It is time taking to execute the given application with different cache sizes on an
instruction set simula
tor (ISS) to figure out the optimal cache size. In this paper, a technique is proposed to
identify a number of cache lines and cache line size for the L1 instruction cache that will offer best or
nearly best IPC. Cache size is derived, at a higher abstract
ion level, from basic block analysis in the Low
Level Virtual Machine (LLVM) environment. The cache size estimated from the LLVM environment is cross
validated by simulating the set of benchmark applications with different cache sizes in SimpleScalar’s out
-
of
-
order simulator. The proposed method seems to be superior in terms of estimation accuracy and/or
estimation time as compared to the existing methods for estimation of optimal cache size parameters (cache
line size, number of cache lines).
AN ATTEMPT TO IMPROVE THE PROCESSOR PERFORMANCE BY PROPER MEMORY MANAGEMENT F...IJCSEA Journal
The performanceof the processor is highly dependent on the regular supply of correct instruction at the right time. Whenever a data miss is occurring in the cache memory the processor has to spend more cycles for the fetching operation. One of the methodsused to reduce instruction cache miss is the instruction prefetching,which in turn will increase instructions supply to the processor.The technology developments in these fields indicates that in future the gap between processing speeds of processor and data transfer speed of memory is likely to be increased. Branch Predictor play a critical role in achieving effective performance in many modernpipelined microprocessor architecture.
Prefetching canbe done either with software or hardware. In software prefetching the compiler will insert a prefetch code in the program. In this case as actual memory capacity is not known to the compiler and it will lead to some harmful prefetches. In hardware prefetching instead of inserting prefetch code it will make use of extra hardware and which is utilized during the execution. The most significant source of lost performance when the process waiting for the availability of the next instruction. Thetime that is wasted in case of branch misprediction is equal to the number of stages in the pipeline, starting from fetch stage to execute stage. All the prefetching methods are givenstress only to the fetching of the instruction for the execution, not to the overall performance of the processor. The most significant source of lost performance is,when the process is waiting for the availability of the next instruction. The time that is wasted in case of branch misprediction is equal to the number of stages in the pipeline, starting from fetch stage to execution stage.This paper we made an attempt to study the branch handling in a uniprocessing environment, whenever branching is identified instead of invoking the branch prediction the proper cache memory management is enabled inside the memory management unit.
STUDY OF VARIOUS FACTORS AFFECTING PERFORMANCE OF MULTI-CORE PROCESSORSijdpsjournal
Advances in Integrated Circuit processing allow for more microprocessor design options. As Chip Multiprocessor system (CMP) become the predominant topology for leading microprocessors, critical components of the system are now integrated on a single chip. This enables sharing of computation resources that was not previously possible. In addition the virtualization of these computation resources exposes the system to a mix of diverse and competing workloads. On chip Cache memory is a resource of primary concern as it can be dominant in controlling overall throughput. This Paper presents analysis of various parameters affecting the performance of Multi-core Architectures like varying the number of cores, changes L2 cache size, further we have varied directory size from 64 to 2048 entries on a 4 node, 8 node 16 node and 64 node Chip multiprocessor which in turn presents an open area of research on multicore processors with private/shared last level cache as the future trend seems to be towards tiled architecture executing multiple parallel applications with optimized silicon area utilization and excellent performance.
This document discusses multicore computers and their organization. It describes how hardware performance issues around increasing parallelism and power consumption led to the development of multicore processors. Multicore computers combine two or more processors on a single chip for improved performance. The main variables in multicore organization are the number of cores, levels of cache memory, and whether cache is shared.
This paper investigates the effects of cache coherence protocols on the performance of multicore network processors. Simulation results show that token-based coherence protocols provide significantly higher performance than directory-based protocols for network workloads. With an 8-core configuration, a token protocol improves performance over directory protocols by a factor of nearly 4 on average. The paper also finds that most shared L2 cache misses are coherence misses, and these misses along with multithreading overhead reduce performance in multicore environments. Future work will focus on reducing these overheads to enhance multicore network processor performance.
Analysis of Multicore Performance Degradation of Scientific ApplicationsJames McGalliard
This document analyzes performance degradation of scientific applications on multi-core systems. It summarizes benchmark results from dual-core and quad-core systems running Department of Defense applications. The tests show a runtime performance penalty for multi-core runs compared to single-core runs on the same systems. This is attributed to contention for memory bandwidth between cores, as shown by synthetic memory benchmark results, consistent with reported studies. The document outlines the benchmark systems used, prior study findings on multi-core performance issues, and analysis of application and memory benchmark results on the multi-core systems.
This document reviews parallel computing and compares different parallel programming models. It discusses CPU and GPU architectures, highlighting that GPUs are designed for massive parallelism while CPUs balance computing power and flexibility. The document evaluates programming models based on supported system architectures, programming interfaces, workload partitioning, task assignment, synchronization methods, and communication models.
This document discusses computer architecture and trends in computer performance. It covers topics like computer architecture definitions, design goals that influence architecture choices, factors that affect performance like instructions per cycle and clock speed, different types of memory and their speeds, trends in processor architecture over time including increasing transistor counts and multicore processors, and how latency and bandwidth impact network and system performance. It also provides some interesting historical facts about competition between Intel and AMD in the CPU market.
I understand that physics and hardware emmaded on the use of finete .pdfanil0878
I understand that physics and hardware emmaded on the use of finete element methods to predict
fluid flow over airplane wings,that progress is likely to continue. However, in recent years, this
progress has been achieved through greatly increased hardware complexity with the rise of
multicore and manycore processors, and this is affecting the ability of application developers to
achieve the full potential of these systems. currently performance is measured on a dense
matrix–matrix multiplication test which has questionable relevance to real applications.the
incredible advances in processor technology and all of the accompanying aspects of computer
system design, such as the memory subsystem and networking
In embedded it seems to combination of both hardware and the software , it is used to be
combined function of action in the systems .while we do that the application to developed in the
achieve the full potential of the systems in advanced processer technology.
Hardware
(1) Memory
Advances in memory technology have struggled to keep pace with the phenomenal advances in
processors. This difficulty in improving the main memory bandwidth led to the development of a
cache hierarchy with data being held in different cache levels within the processor. The idea is
that instead of fetching the required data multiple times from the main memory, it is instead
brought into the cache once and re-used multiple times. Intel allocates about half of the chip to
cache, with the largest LLC (last-level cache) being 30MB in size. IBM\'s new Power8 CPU has
an even larger L3 cache of up to 96MB [4]. By contrast, the largest L2 cache in NVIDIA\'s
GPUs is only 1.5MB.These different hardware design choices are motivated by careful
consideration of the range of applications being run by typical users.
One complication which has become more common and more important in the past few years is
non-uniform memory access. Ten years ago, most shared-memory multiprocessors would have
several CPUs sharing a memory bus to access a single main memory. A final comment on the
memory subsystem concerns the energy cost of moving data compared to performing a single
floating point computation.
(2) Processors
CPUs had a single processing core, and the increase in performance came partly from an increase
in the number of computational pipelines, but mainly through an increase in clock frequency.
Unfortunately, the power consumption is approximately proportional to the cube of the
frequency and this led to CPUs with a power consumption of up to 250W.CPUs address memory
bandwidth limitations by devoting half or more of the chip to LLC, so that small applications can
be held entirely within the cache. They address the 200-cycle latency issue by using very
complex cores which are capable of out-of-order execution , By contrast, GPUs adopt a very
different design philosophy because of the different needs of the graphical applications they
target. A GPU usually has a number of functional u.
DESIGNED DYNAMIC SEGMENTED LRU AND MODIFIED MOESI PROTOCOL FOR RING CONNECTED...Ilango Jeyasubramanian
This document proposes and evaluates several cache designs for improving performance and energy efficiency in multi-core processors. It introduces a filter cache shared among cores to reduce energy consumption. It then implements a segmented least recently used replacement policy and adaptive bypassing to further improve cache hit rates. Finally, it modifies the MOESI coherence protocol for a ring interconnect topology to address data coherence across cores. Simulations show the proposed cache designs reduce energy usage by 11% and increase cache hit rates by up to 7% compared to baseline designs.
The document summarizes the memory performance limitations of Intel Xeon microprocessors based on the Nehalem and Westmere architectures. It finds that per core and per thread memory bandwidth is restricted to about 1/3 of theoretical maximum values. Moving from Nehalem to Westmere, read performance scales well but write performance suffers, revealing scalability issues in Westmere's design. The document aims to provide an accurate analysis of memory bandwidth and latency limitations to help application developers optimize code efficiency.
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Do elements of globalization, such as Foreign Direct Investment (FDI), negatively affect the ability of countries in the Global South to preserve their culture? This research aims to answer this question by employing a cross-sectional comparative case study analysis utilizing methods of difference. Thailand and Cambodia are compared as they are in the same region and have a similar culture. The metric of difference between Thailand and Cambodia is their ability to preserve their culture. This ability is operationalized by their respective attitudes towards FDI; Thailand imposes stringent regulations and limitations on FDI while Cambodia does not hesitate to accept most FDI and imposes fewer limitations. The evidence from this study suggests that FDI from globally influential countries with high gross domestic products (GDPs) (e.g. China, U.S.) challenges the ability of countries with lower GDPs (e.g. Cambodia) to protect their culture. Furthermore, the ability, or lack thereof, of the receiving countries to protect their culture is amplified by the existence and implementation of restrictive FDI policies imposed by their governments.
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REDUCING COMPETITIVE CACHE MISSES IN MODERN PROCESSOR ARCHITECTURES
1. International Journal of Computer Science & Information Technology (IJCSIT) Vol 8, No 6, December 2016
DOI:10.5121/ijcsit.2016.8605 49
REDUCING COMPETITIVE CACHE MISSES IN
MODERN PROCESSOR ARCHITECTURES
Milcho Prisagjanec and Pece Mitrevski
Faculty of Information and Communication Technologies,
University “St. Kliment Ohridski”, Bitola, Republic of Macedonia
ABSTRACT
The increasing number of threads inside the cores of a multicore processor, and competitive access to the
shared cache memory, become the main reasons for an increased number of competitive cache misses and
performance decline. Inevitably, the development of modern processor architectures leads to an increased
number of cache misses. In this paper, we make an attempt to implement a technique for decreasing the
number of competitive cache misses in the first level of cache memory. This technique enables competitive
access to the entire cache memory when there is a hit – but, if there are cache misses, memory data (by
using replacement techniques) is put in a virtual part given to threads, so that competitive cache misses are
avoided. By using a simulator tool, the results show a decrease in the number of cache misses and
performance increase for up to 15%. The conclusion that comes out of this research is that cache misses
are a real challenge for future processor designers, in order to hide memory latency.
KEYWORDS
Memory-Level Parallelism, Cache Memory, Competitive Cache Misses, Multicore Processor,
Multithreading
1. INTRODUCTION
The main objective in the development of a processor is its performance increase, and the
bottlenecks are being eliminated by implementation of different types of techniques in the
architecture itself. By following this timeline historically, one can note that the frequency
increase, the implementation of out-of-order execution of the instruction stream, the enlargement
of the instruction window, and the Instruction-Level Parallelism (ILP), all contributed to
increasing the performances of processors in some periods of time [1].
But, according to some authors, the gap between processor and memory speeds, which has
existed since the very appearance of computers, despite many offered techniques (some of which
have been already implemented in commercial processors), is the reason for performance decline
[2]. An instruction that accesses memory, until it is complete with memory data, blocks the
processor resources at the same time and thus decreases performance. When the processor needs
memory data, and data are found in the first level cache, one says that there is a hit. Otherwise, a
cache miss occurred and the memory system starts a procedure of elimination, which may take
several hundred cycles [3].
The main reasons for performance decline and increased number of cache misses in modern
processor architectures are the memory shared among cores, as well as the drift towards
implementation of larger number of cores and threads in the processor itself. Some of the
techniques that are intended to help in reducing cache misses (prefetching, for example), even
contribute to the appearance of such competitive cache misses and decrease performance.
2. International Journal of Computer Science & Information Technology (IJCSIT) Vol 8, No 6, December 2016
50
The aim is to find a technique which would enable for reducing memory latency and the number
of cache misses in commercial processors. There are many papers in which authors contribute to
the increase of Memory-Level Parallelism, but none of these has been implemented in
commercial processors to date. Others go even further, stating that it is necessary to abandon
Instruction-Level Parallelism and that researchers should completely turn to Memory-Level
Parallelism instead [4].
Taking that into consideration, after we review related work in Section 2 and analyze the
performance impact of competitive cache misses in Section 3, we propose a technique for
reducing competitive cache misses. The suggestion is every single thread to have its own
“virtual” cache memory in the first level during block replacement, while using the entire cache
memory during loading. On the positive side are the easy way of implementation, and the fact
that it does not “revolutionary” change the present architecture of the processor. But, on the
negative side, one should note that the cache memory is used far below par in the first level
during not very intensive processor workload, as we will demonstrate in Section 4. Section 5
concludes the paper.
2. RELATED WORK
The research made by many authors showed that cache misses reduce the processor performance
even up to 20%. Even more significant information is that the gap between the processor and
memory speeds is getting deeper and bigger through time, which contributes to a larger number
of cache misses. This was the main motivation for various efforts to design techniques that reduce
cache misses. For example, the prefetching technique [5], which has been implemented in
commercial processors, supplies memory data by fetching them into the cache memory before the
processor needs them. Some other authors [6] have given ideas of a virtual enlargement of the
instruction window, so that it would be possible to unlock the processor’s resources in the
window and to load in advance memory data which are to be used by the processor in the near
future. They provide a technique for virtual extension of the instruction window, which is called
runahead execution. The idea is to enable continued operation of the processor when its resources
are blocked by a long latency instruction. In this manner, memory data prefetching from the first
level cache is enabled.
The idea for the improvement of processor performance by implementing Memory-Level
Parallelism (MLP) techniques has been used in a number of research papers. Models that reduce
memory latency and/or the number of cache misses are given herewith. Continual Flow Pipelines
[7] aim to remove the long latency instruction together with its dependent instructions, so that
resources would be released and the processor could execute the independent instructions. In [8],
the author suggests a Recovery-Free Value Prediction technique, whose idea relates to speculative
execution in order to load memory data from the first level cache. Out-of-order commit [9] is a
technique which enables the execution of the instructions in the absence of a reordering buffer. In
other words, by increasing the instruction window, there is a need for a constant increase of the
reordering buffer which, in turn, increases the complexity of the processor. This technique allows
to completely leave out the reordering buffer.
3. COMPETITIVE CACHE MISSES AND PERFORMANCE IMPACT
The lack of ability to burst through the technological cutbacks in processor design, changes the
course in their development. That means that the idea is to design an architecture which would
perform multiple numbers of instructions at the same clock frequency. The first-hand concept is
based on a system in supercomputers known beforehand, where many computers execute their
workload in parallel. This architecture is modified by using more processor cores placed on one
3. International Journal of Computer Science & Information Technology (IJCSIT) Vol 8, No 6, December 2016
51
silicon crystal. Each of the cores is a processor itself, but the new architecture significantly
reduces energy dissipation. The trends of increasing the number of cores and threads are more
present in modern processor architectures – they impose the necessity of a larger instruction
window. By doing so, there is an increasing number of instructions which have greater need of
memory data, whose latency is too big and causes stagnation in the work of the processor.
3.1. PERFORMANCES OF MULTI CORE PROCESSORS
In the best case, dual core processor should complete a programmer’s code twice as fast,
compared to a single core processor. But the practical cases so far showed that it does not really
happen, and that the double core processor is only 1.5 times faster than a single core processor.
Surprisingly, in some scenarios, single core processors even show better performances – one of
the reasons are cache misses.
In [10], by means of a simulator, a single core processor has been designed. First level (L1) of
cache memory is composed of instructional cache and data cache (2 x 64 Kbytes), L2 cache
memory with a size of 256 Kbytes and L3 cache memory with a size of 512 Kbytes. The
remaining parameters are configured according to the parameters of the commercial processors.
The tests have been performed in architectures of one-level, two-level, and three-level cache
memory. The results of the experimental tests are shown in Table 1. They show that there are
misses at every level of cache memory: in L1 cache memory there are 88% hits and 12% misses.
From the misses in L1 cache memory, 8.7% are next level cache memory misses (i.e. L2),
whereas 5.3% of these misses are from the last (L3) cache memory level. The analysis shows that
with the development of the new commercial architectures of processors and with the increase in
the number of cores, there is also an increase in the number of cache misses, which reduce the
performances of the processor.
Table 1. Cache misses in presence of memory hierarchy.
Architecture
of cache
memory
Cache memory
Number of accesses
Cache misses
in L1
Cache misses
in L2
Cache misses
in L3
2x64+256+512 20000 2560 224 12
An analysis of the cache misses has been done depending on the number of the cores. By using a
simulator, a multicore processor has been designed with only L1 cache memory with capacity of
512 Kbytes (i.e. 256 Kbytes of instruction cache and 256 Kbytes of data cache). The bus supports
MESI protocol for maintaining memory coherence. The main memory capacity is 1 GB.
Benchmarks of the designed processor have been executed by changing the number of processor
cores. The results are shown in Fig. 1.
Figure 1. How the number of processor cores affects cache misses
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One can see that the number of cache misses for the simulated architecture is 10% of the number
of memory accesses. But it can also be concluded that by increasing the number of cores above
16, the number of cache misses increases as well, which has a negative effect on processor
performance. One of the reasons for that is the competitive cache misses.
3.2. COMPETITIVE CACHE MISSES
In modern processor architectures, a number of cores and threads share the same memory, and the
workload that the processor has to undertake is divided into processes and threads. Every process
needs certain memory data, and if it cannot provide them from the first level cache, it loads them
from the memory subsystem by using a certain method for changing the blocks. This methods do
not usually check if a block, which is currently being changed, would be used in near future by
some other processes. Namely, it leads to removal of some memory blocks, which might be
needed by some other active processes in subsequent cycles. As a result, it would cause a
decrease in processor performance.
This situation would become even worse if prefetching was used to load memory data from the
first level cache. If every process would use this technique to load memory data from the first
level of cache memory, which it would need in near future, due to the restricted capacity of the
cache memory and its shared use, would cause competitive memory access and mutual removal
of the blocks of data for the processes. The possibility of appearance of the competitive cache
memory access grows with processor workload, with the increasing of the number of cores and
threads that share the same memory, and finally because of the restricted capacity of the cache
memory of the processor.
4. REDUCING COMPETITIVE CACHE MISSES – TECHNIQUE AND BENEFITS
To avoid competitive access of the threads, we suggest the technique of a one-way shared cache
memory. The first level cache is shared to as many parts as the number of threads. All threads
competitively access the memory. If a thread contains an instruction that accesses the memory, a
check is performed whether the required memory data are available. Therefore, if these data can
be found in the first level cache, then they are being loaded. So far, it is the same as in all the
modern processor architectures. If the data cannot be found in the first level of the cache memory,
then it is necessary to be loaded from another level of the memory subsystem. The loading of the
memory block is completed by using one of the known replacement techniques, but by doing so
the block can be loaded only in the part of the cache memory, which belongs to the thread. That
means that, during loading memory data, the thread uses all the shared cache memory from the
first level. But if certain data do not exist in the first level, then it loads them from the memory
subsystem, but only in its own “virtual” part of the cache memory.
The prefetching technique, which is frequently used in modern processor architectures, is another
reason for the appearance of competitive cache misses. Principally, this technique is implemented
in order to decrease memory latency and the number of cache misses. In order to get a picture for
the benefits of using the data prefetching technique, a processor has been tested and the number
of cache misses depending on the number of prefetched data has been determined by using a
simulator tool. In Fig. 2 it can be seen how the number of cache misses changes according to the
number of prefetched instructions – in the interval of 4 to 6 prefetched instructions the number of
cache misses is very close to 0.
With the results in this part we have further confirmed the efficiency of data prefetching in
reducing the number of cache misses. However, this efficiency is optimal only if the prefetching
system makes a correct prediction of the memory data that should be fetched and when to start the
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fetching process. This means that, for the instructions that access the memory, this technique
makes early loading of memory data and places them in the first level cache. At the moment of
execution of the instruction the memory data are already in the cache memory and the processor
just takes them from there with minimum delay. But, in modern processor architectures, there is
competitive access of the threads to the first level cache with the prefetching technique. That is
the reason for competitive access to the same memory address while loading the memory data
from the upper levels of the cache memory.
Figure 2. Number of cache misses depending on the number of prefetched instructions
4.1. SIMULATION ENVIRONMENT
In order to get measurable and comparable performance evaluation results, we designed a
processor simulator by using the Python programming language [11]. SimPy (Simulation in
Python) [12] is an object-oriented, process-based discrete-event simulation language based on
standard Python, which provides the modeler with components of a simulation model including
“Processes” (active components) and “Resources” (passive components) and provides monitor
variables to assist in gathering statistics. Discrete-event simulation (DES) utilizes a
mathematical/logical model of a physical system that portrays state changes at precise points in
simulation time. Both the nature of the state changes and the time at which the changes occur,
require precise description. Within DES, time advances not at equal size time steps, but rather
until the next event can occur, so that the duration of activities determines how much the clock
advances. “Process Execution Methods” (PEMs) use the “yield hold” command to temporarily
delay process objects’ operations. Figs. 3-7 show the program codes of the “RAM Memory” and
“Instruction Pointer” resources, as well as the “Decoding”, “Execution” and “Cache” processes,
respectively.
Figure 3. Program code of the “RAM Memory” resource in SimPy
Figure 4. Program code of the “Instruction Pointer” resource in SimPy
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Figure 5. Program code of the “Decoding” process in SimPy
Figure 6. Program code of the “Execution” process in SimPy
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Figure 7. Program code of the “Cache” process in SimPy
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4.2. PERFORMANCE BENEFITS
Next we tested the performances of an ideal processor without cache misses, a multithreaded
processor, and a processor where we implemented the proposed technique for non-competitive
access to the cache memory in the first level. The results gained from the tests are shown in
Fig. 8. The offered technique is implemented in a single core multithreaded processor with 4
threads. The simulator makes parallel execution of the instructions in all of the threads. When the
simulator comes to an instruction with access to the memory, it checks whether data can be found
in the L1 cache memory. If there is a hit, it loads memory data and completes the instruction. But,
if a miss in L1 cache memory occurs, the simulator searches these memory data in the upper
levels of the memory hierarchy. The simulator uses the technique of block replacement and loads
the memory data only in the virtual part of L1 cache memory, which belongs to the matching
thread.
According to the results shown, the technique offered makes the time of execution of a program
shorter for 15%. The source of this finding is the decreased number of competitive cache misses
in the first level cache. The good side of the offered technique is that it does not “revolutionary”
change the architecture of the processors. It can be implemented very easily: the change comes
only in the technique of block replacement in the first level cache. A tag is used for marking
which block belongs to which thread. While replacing the memory block, this tag is used to
virtually divide cache memory by the number of threads that access the memory.
The prefetching technique is not something novel: the change only means that this technique
early loads memory data in the second level of the cache memory, to avoid competitive access to
the first level. It does not increase processor complexity, and so, it does not cause additional
energy dissipation. The disadvantages of this technique, however, are the low exploitation of the
first level cache during a poor workload of the processor. In cases with a small number of
processes that reduces the number of active threads, as well, it effectively reduces the available
capacity of the first level cache.
Figure 8. Graphical overview of the performances of three types of processors
5. CONCLUSIONS
The simulation results showed again the huge impact of cache misses on processor performance –
the decreased processor performance due to cache misses cannot be ignored. The offered
technique succeeds in decreasing the number of cache misses for about 15%, and it increases
processor performance. Different studies have come to a conclusion that the number of cache
misses in modern processor architectures is still outsized. On the other side, the direction in which
they develop (by increasing the number of cores and threads, and by using shared cache memory),
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brings about the appearance of bigger number of cache misses even more, and decreases
processor performance. Our research certified again that the cache misses significantly reduce
performances, and that decreasing the number of cache misses is a great challenge to future
research and processor designers.
REFERENCES
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[11] URL < http://www.python.org/>
[12] URL < http://simpy.sourceforge.net/>
Authors
Milcho Prisagjanec received his BSc degree in Electrical Engineering from the Faculty of
Electrical Engineering and Information Technologies at the Ss. Cyril and Methodius
University in Skopje, and the MSc degree from the Faculty of Technical Sciences,
University “St. Kliment Ohridski” – Bitola, Republic of Macedonia. He is currently a system
administrator and a PhD student at the Faculty of information and Communication
Technologies. His field of interest is performance and reliability analysis of computer and
communications systems.
Pece Mitrevski received his BSc and MSc degrees in Electrical Engineering and Computer
Science, and the PhD degree in Computer Science from the Ss. Cyril and Methodius
University in Skopje, Republic of Macedonia. He is currently a full professor and Dean of
the Faculty of Information and Communication Technologies, University “St. Kliment
Ohridski” – Bitola, Republic of Macedonia. His research interests include Computer
Architecture, Computer Networks, Performance and Reliability Analysis of Computer
Systems, e-Commerce, e-Government and e-Learning. He has published more than 100 papers in journals
and refereed conference proceedings and lectured extensively on these topics. He is a member of the IEEE
Computer Society and the ACM.