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School of Computer Science & Engineering
University of New South Wales
Advanced Operating Systems
COMP9242 2002/S2

Next: Case in Point: LLinux [Härtig Up: 05-uk Previous: A Critique of the

Subsections

$\mu$ -kernel Design Principles

Minimality:

If it doesn't have to be in the kernel, it shouldn't be in the kernel

Appropriate abstractions

which can be made fast
and allow efficient implementation of services

Well written:

It pays to shave a few cycles off
TLB refill handler or the IPC path

Unportable:

must be targeted to specific hardware

$.$: no problem if it's small, and higher layers are portable
$.$: Example: Liedtke reports significant rewrite of memory management when porting from 486 to Pentium
==>: ``abstract hardware layer'' is too costly

Non-portability example: i486 vs Pentium:

Appropriate system calls to reduce number of kernel invocations
- e.g., reply & receive next
Rich message structure
- value and reference parameters in message
Copy message only once (i.e. not user $\rightarrow$ kernel $\rightarrow$ user)
Short messages in registers
As many syscall parameters in registers as possible
One kernel stack (for interrupt handling) per thread (in TCB)

Next: Case in Point: LLinux [Härtig Up: 05-uk Previous: A Critique of the

Gernot Heiser 2002-08-28

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