The document describes the design and implementation of EKernel, an object-oriented microkernel. It aims to address issues of portability, maintainability, extensibility, and efficiency in operating system design. The key aspects of EKernel's design include using processes and threads as core abstractions, implementing inter-process communication via messaging, and providing a modular architecture with well-defined interfaces. Performance tests show EKernel achieves lower overhead than other microkernels for operations like context switches and IPC. Future work plans to enhance EKernel's scheduler and implement a networking subsystem.

1. 1999/6/11 Murphy Cheng-Che Chen 1
The Design and Implementation of
EKernel: An Object-Oriented µ-kernel
Cheng-Che Chen, Sheng-De Wang
Department of Electrical Engineering
National Taiwan University
murphy@yours.com, sdwang@cc.ee.ntu.edu.tw

2. Murphy Cheng-Che Chen 2
Outline
• Motivation
• Introduction
• EKernel Design
• Performance Measure
• Conclusion and Future Work

3. Murphy Cheng-Che Chen 3
Motivation
• Problems
– Continuously evolving processors
– Demanding applications
• Issues
– Portability, Maintainability,
Extensibility and Efficiency.

4. Murphy Cheng-Che Chen 4
IntroductionIntroduction

5. Murphy Cheng-Che Chen 5
Operating System
• A layer of software on a bare machine.
• Resource management.
– Scheduling, Storage, IPC, etc...
• User friendliness.
– Execution environment (process
management, file, interrupt, I/O)

6. Murphy Cheng-Che Chen 6
Operating System
E n d U s e r
A p p l i c a t i o n
P r o g r a m s
U t i l i t i e s
O p e r a t i n g S y s t e m
C o m p u t e r H a r d w a r e
P r o g r a m m e r
O p e r a t i n g S y s t e m
D e s i g n e r

7. Murphy Cheng-Che Chen 7
Kernel
• The mandatory part of an operating
system common to all other software.
• Under supervisor mode
• Accessing hardware resources for
user applications

8. Murphy Cheng-Che Chen 8
Monolithic Kernel
• The whole operating system is packed
into a single large kernel.
• Efficiency (all modules are under the
same address space)
• Complex
• Very hard to adapt or extend.

9. Murphy Cheng-Che Chen 9
µ-kernel
• Only extremely essential primitive
operating system functions should be
put into the kernel.
• Other operating system services are
built on top of the µ-kernel.
• OS components communicate with
each other via messages.

10. Murphy Cheng-Che Chen 10
Advantages of µ-kernel
• A better modular system structure
could be enforced by a clear µ-kernel
interface.
• A server malfunction is isolated as
any other user program’s.
• The system is more flexible and tailor-
able, different policies can coexist.

11. Murphy Cheng-Che Chen 11
2nd Generation µ-kernel
• Problems of µ-kernels
– Performance degradation
– Inherited from monolithic kernels
• Radical new designs
– Exokernel (no abstractions)
– L3/L4 (minimal set of µ-kernel
abstractions, non-portable)

12. Murphy Cheng-Che Chen 12
EKernel DesignEKernel Design

13. Murphy Cheng-Che Chen 13
Abstractions
• Process
• Thread
• Interprocess Communication

14. Murphy Cheng-Che Chen 14
Process
• Basic unit of resource allocation.
• Has its own address space.
• In Ekernel, traditional operating
systems, windowing systems and
device drivers are all processes.

15. Murphy Cheng-Che Chen 15
Thread
• Basic unit of CPU utilization.
• Shares with peer threads its code
section, data section, address space
and resources.
• Has its own stack and execution
context.

16. 09/16/18 Murphy Cheng-Che Chen 16
Inter-process Communications
• Allow threads to communicate with
each other and to synchronize their
actions.
• Highly related to the internal data
structure of threads and processes.
• Messaging, Semaphore, Mutex and
Event.

17. A p p lic a t io n
P r o c e s s
A p p lic a t io n
P r o c e s s
N e t w o r k in g
P r o c e s s
S e r ia l
P o r t
P r o c e s s
W in d o w in g
P r o c e s s
F ile
S y s t e m
S e r v e r
S h a r e d
L ib r a r y
S h a r e d
L ib r a r y
U s e r S p a c e
K e r n e l S p a c e
S y s t e m C a ll I n t e r f a c e
P r o c e s s
C o n t r o l
T h r e a d
C o n t r o l
S y n c h r o n iz a t io n
M e c h a n is m
S c h e d u le r
H a r d w a r e P la t f o r m
H a r d w a r e
E x c e p t io n
H a n d lin g
A p p lic a t io n
P r o c e s s
A p p lic a t io n
P r o c e s s
M e m o r y
M a n a g e m e n t

18. EMicro
ENano
ProcessorMMU
Interrupt
Controller
Process
Thread
Scheduler
Memory
Allocator
Semaphore
Event
Mutex
Message Queue
SystemCall
Dispatcher
Interrupt
Dispatcher

19. Murphy Cheng-Che Chen 19
Processor
• Purpose
– Abstract generic mechanisms
provided by most processor.
• Exported Function
– EnableInterrupt, DisableInterrupt
– SetThreadContext
– SwitchContext

20. Murphy Cheng-Che Chen 20
MMU
• Purpose
– Abstracts the memory management unit.
• Exported Function
– EnablePaging, DisablePaging
– SwitchPageTable
– PageTableMapRangeKernel,
PageTableMapRangeUser

21. Murphy Cheng-Che Chen 21
InterruptController
• Purpose
– Abstract generic interrupt controllers
• Exported Function
– DisableIRQ, EnableIRQ, DisableAllIRQ,
EnableAllIRQ
– AcknowledgeIRQ
– HookIRQ

22. Murphy Cheng-Che Chen 22
Process and Thread
• Purpose
– Maintain basic information as well as interfaces for
accessing such information.
• Process
– Process ID, Process Name, Thread List,
Memory Manager
• Thread
– Thread ID, Thread Name, Process ID

23. Murphy Cheng-Che Chen 23
Scheduler
• Purpose
– Select a thread from ready queue and allocate
CPU to it.
• Data
– Ready Queue
• Exported Function
– Schedule, Check-In, Check-Out, Disable-
Preemption, Enable-Preemption, Yield

24. Murphy Cheng-Che Chen 24
IPC
• Include: MessageQueue, Semaphore,
Mutex and Event objects.
• Interact with Scheduler object
– when they need to block the
execution of a thread
– when some thread in their waiting
queues is ready for execution

25. Murphy Cheng-Che Chen 25
SystemCallDispatcher
• Purpose
– Provides the interface between a
process and the operating system
kernel.
• Exported Function
– HookSystemCall
– Dispatch

26. Murphy Cheng-Che Chen 26
InterruptDispatcher
• Purpose
– Notify a thread that an interrupt has
occurred.
• Exported Function
– HookInterrupt
– Dispatch

27. Murphy Cheng-Che Chen 27
Driver Architecture
• Device drivers
– Are allowed to execute in user space.
– Invoke system services to
• hook interested interrupts
• request access rights to I/O
– Can be combined with a server process to
minimize data paths.

28. Murphy Cheng-Che Chen 28
Portability
• Two layers: ENano and EMicro.
• To port EKernel, we need to
– Write hardware specific codes for the
actual implementation classes and have
them derived from ENano objects.
– In kernel initialization, point the global
variables of ENano to the instances of the
newly derived classes.

29. Murphy Cheng-Che Chen 29
Extensibility
• Take the scheduler for example
– Inherit a new class PriorityThread from the class
Thread
– Add a function CreatePriorityThread that calls
original CreateThread and records additional
information
– Implement the new scheduling algorithm in
CheckIn, CheckOut, GetNext of Scheduler.

30. Murphy Cheng-Che Chen 30
PerformancePerformance
MeasureMeasure

31. Murphy Cheng-Che Chen 31
User-Kernel Switches
• Measures the overhead in doing a
system call.
System CPU, MHz Cycle
L3 486, 50 123 – 180
Ekernel Pentium, 100 186
Mach RS2000, 16.7 900

32. Bare Machine Page Table Switch Cycles
486 36 … 364
Pentium 36 … 1196
Operating System Address Space Switch Cycles
Ekernel ( on Pentium ) 863
Murphy Cheng-Che Chen 32
Address Space Switches
• Includes page table switching, TLB
flushing, and cache flushing.

33. Murphy Cheng-Che Chen 33
IPC
• Round-trip IPC overhead includes sending/receiving a
message, user-kernel switch, address space switch.
System CPU, MHz Cycles / IPC
Ekernel1 Pentium, 100 231
L3 486, 50 250
QNX 486, 33 1254
Ekernel2 Pentium, 100 1492
Mach RS2000, 16.7 1584
SRC RPC CVAX, 12.5 2900
Mach 486, 50 5750
Amoeba 68020, 15 6000
Spin Alpha 21064, 133 6783
Mach Alpha 21064, 133 6916

34. Murphy Cheng-Che Chen 34
Conclusion AndConclusion And
Future WorkFuture Work

35. Murphy Cheng-Che Chen 35
Conclusion
• We’ve designed an object-oriented micro-kernel
which tries to tackle the problems of portability,
maintainability, extensibility and efficiency.
• We’ve implemented EKernel on Pentium
processors.
• The performance measure shows that we’ve
adroitly tackled the conflicting issues of flexibility
and efficiency.

36. Murphy Cheng-Che Chen 36
Future Work
• Extend the basic round-robin scheduler of
EKernel to support multimedia applications
as well as real-time applications.
• Build a networking sub-system which
encompasses the TCP/IP stack together
with the networking driver to verify the
effectiveness of EKernel driver architecture.