This presentation is about various aspects of low-level optimization: productivity and consumption of various data structures, hidden pitfalls of popular approaches and templates, thread synchronization, memory access methods, effective processor cache usage and more. This presentation by Andrii Antilikatorov (Consultant, GlobalLogic) was delivered at GlobalLogic Kharkiv .NET Conference on July 5, 2016.

1. ©2016 GlobalLogic Inc.

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.NET Performance Boost
By Andrii Antilikatorov

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Optimize or not optimize?

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Quiz

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Jagged arrays vs 2D arrays
4571ns2864ns

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Jagged arrays

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FOR vs FOREACH

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FOR vs FOREACH
… it depends

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FOR vs FOREACH

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Performance of try...catch
2555ns 674ns

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Create new collection or clear existing one?
645ns
501ns

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String pool
Can be disabled with CompilationRelaxationsAttribute
By default interns only string literals
Works great in multithreaded code
Has the same lifetime as CLR
May cause troubles if interning went out of control

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Avoiding Boxing
bool areEqual = v1.Equals(v2);

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Avoiding Boxing
bool areEqual = v1.Equals(v2);

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Avoiding Boxing

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Avoiding Boxing

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Avoiding Boxing

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Avoiding Boxing

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Avoiding Boxing
Use value types if objects are small and supposed to be used often.
Value types are useful for memory compaction.
Override Equals(), “==“ (“!=“). Implement IEquatable interface.
Override GetHashCode().
Make value types immutable.

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Cost of method calls
CALL
CALLVIRTDependency Injection

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Parameter order performance
952ms
2224ms

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Field access optimization
15.86ns

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Field access optimization
5.18ns

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Multiple return values
1.64ns
0.32ns
5.40ns

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Tuple/KeyValuePair performance
Tuple KeyValuePair
Allocate 8.23ns 0.32ns
Pass as argument 1.93ns 2.57ns
Return 6.09ns 1.91ns
Load from List 2.79ns 4.18ns

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Array Copy
1343ns
1013ns

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Performance of DateTime
264ns
16 ns

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Memory Access
Off-Heap
(Unmanaged)
Memory-Mapped Files
Heap
(Managed)
1.068s1.096s
LOH optimization
P/Invoke, COM, Marshalling

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Memory-Mapped Files
Ideal to access file on disk without
performing I/O operations
The most efficient for cross-
process communication.
Allows properly protecting the
content and synchronize access.

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Memory Alignment
Type alignment Page size alignment
Cache line alignment
Memory Alignment

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Comparing Aligned/Unaligned Access Performance
Type aligned access provides better performance than
unaligned access.
Memory access that spans 2 cache lines has far worse
performance than aligned mid-cache line access.
Cache line access performance changes based on
cache line location.

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Type-aligned vs unaligned Access Test
Number of pages
Alignment
Relative cost

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Comparing Aligned/Unaligned Access Performance
Type aligned access provides better performance than
unaligned access.
Memory access that spans 2 cache lines has far worse
performance than aligned mid-cache line access.
Cache line access performance changes based on
cache line location.

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Cross-line cache access
Number of pages
Offset
Relative cost

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Comparing Aligned/Unaligned Access Performance
Type aligned access provides better performance than
unaligned access.
Memory access that spans 2 cache lines has far worse
performance than aligned mid-cache line access.
Cache line access performance changes based on
cache line location.

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Comparing Aligned/Unaligned Access Performance
Type aligned access provides better performance than
unaligned access.
Memory access that spans 2 cache lines has far worse
performance than aligned mid-cache line access.
Cache line access performance changes based on
cache line location.

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Cost of Access Based on Cache Line Location
Offset
Number of pagesRelative cost

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Comparing Aligned/Unaligned Access Performance
Type aligned access provides better performance than
unaligned access.
Memory access that spans 2 cache lines has far worse
performance than aligned mid-cache line access.
Cache line access performance changes based on
cache line location.

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Synchronized or volatile?
Volatile variables are less expensive than synchronized blocks
Volatile are thread-safe for atomic operations
Volatile acquires lock on variable, therefore not thread- safe
for non-atomic operations
Synchronized blocks have no performance impact if no
synchronization required

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Synchronized or volatile?

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Synchronized or volatile?
MESI Protocol
• Modified
• Exclusive
• Shared
• Invalid

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Synchronized or volatile?
Volatile variables are less expensive than synchronized blocks
Volatile are thread-safe for atomic operations
Volatile acquires lock on variable, therefore not thread- safe
for non-atomic operations
Synchronized blocks have no performance impact if no
synchronization required

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Summary
Architecture first
Remember rule 80/20
Don’t try to write ideal code from the beginning
Don’t create bicycles
Don’t optimize for particular platform

48. ©2016 GlobalLogic Inc.