EKernel is an object-oriented microkernel designed to take advantage of modern processors and meet the demands of various applications. It focuses on portability, maintainability, extensibility, and efficiency. EKernel only includes essential kernel functions and builds other OS services as user-space servers. This modular design improves flexibility. Performance tests show that EKernel has lower overhead for system calls, address space switches, and IPC compared to other microkernels. Future work plans to implement file systems, networking, and other subsystems.

1. 1999/4/19 Murphy Cheng-Che Chen 1
EKernel: An Object-Oriented µ-kernel
Murphy Cheng-Che Chen, Sheng-De Wang
Department of Electrical Engineering
National Taiwan University
murphy@yours.com, sdwang@cc.ee.ntu.edu.tw

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Outline
• Goals / Issues
• Introduction (Kernel /Monolithic Kernel /
µ-kernel /2nd Generation µ-kernel)
• Ekernel Design
• Performance
• Conclusion & Future Works

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Goals
• To take full advantage of continuously
launched processors.
• To meet the demands of various kinds of
applications.

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Issues
• Portability
• Maintainability
• Extensibility
• Efficiency

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Introduction : Kernel
• Kernel
– the mandatory part of an operating
system common to all other software.
– user / supervisor mode.

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Introduction : Monolithic Kernels
• Monolithic Kernels
– The whole operating system was packed
into a single large kernel.
• Opearting Systems
– schedulers, device drivers, memory
managers, file systems, networking
subsystems, etc.

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Introduction : µ-kernel (1)
• µ-kernel
– Only absolutely essential core operating
system functions are put into the kernel.
– Other operating system services are built
on the µ-kernel.

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Introduction : µ-kernel (2)
• The advantages of the µ-kernel approach:
– A more modular system structure could
be enforced by clear µ-kernel interfaces.
– Server malfunction is isolated as any
other user programs.
– The system is more flexible and
tailorable.

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Introduction : µ-kernel (3)
A p p lic a t io n P a g e r
M ic r o k e r n e l
p a g e
f a u lt
r e s u m e R P C

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Introduction : 2nd gen. µ-kernel
• Problems of µ-kernels
– Efficiency
– Inheritance from monolithic kernels
• Radical new designs
– Exokernel ( no abstractions )
– L3/L4 ( minimal set of µ-kernel
abstractions)

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EKernel Design: Abstractions (1)
• Process
– basic unit of resource allocation
• Thread
– basic unit of CPU utilization
• Address Space
– mapping from virtual pages to phyical
pages

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EKernel Design: Abstractions (2)
• Inter-process communication (IPC)
– 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, event.

13. 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
M e s s a g in 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

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

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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.

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Performance:
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

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

18. 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
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Performance: IPC
• RPC overhead includes sending/receiving a message, user-
kernel switch, address space switch.

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Conclusion & Future Works
• Implementation
– currently on Pentium processors.
– porting to other processors.
– efficient and flexible.
• Future Works
– file sub-system, networking sub-system,
window sub-system, multimedia, etc...

20. APPENDIX
09/16/18 Murphy Cheng-Che Chen 20

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class Processor;
• EnableInterrupt
• DisableInterrupt
• SetThreadContext
• SwitchContext

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class MMU;
• EnablePaging
• DisablePaging
• SwitchPageTable
• PageTableMapRangeKernel
• PageTableMapRangeUser

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class InterruptController;
• DisableIRQ
• EnableIRQ
• DisableAllIRQ
• EnableAllIRQ
• AcknowledgeIRQ
• HookIRQ

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class Scheduler;
• Schedule
• CheckIn
• CheckOut
• DisablePreemption
• EnablePreemption
• Yield

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class SystemCallDispatcher;
• HookSystemCall
• Dispatch

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class InterruptDispatcher;
• HookInterrupt
• Dispatch