Linux-kernel mailing list archive 2000-40,: Re: lowish-latency patch for 2.4.0-test9

# Re: lowish-latency patch for 2.4.0-test9

Andi Kleen (ak@suse.de)
Fri, 6 Oct 2000 15:39:20 +0200

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On Fri, Oct 06, 2000 at 10:00:36PM +1100, Andrew Morton wrote:
> The little-low-latency patch for test9 is at
>
> http://www.uow.edu.au/~andrewm/linux/2.4.0-test9-low-latency.patch
>
> Notes:
>
> - It now passes Benno's tests with 50% headroom (thanks to
> Ingo's scheduler race fix).

What was that race exactly ?

There is a scheduler race which may also hurt (and is harder to fix):
when the timer interrupt hits in syscall exit after the need_resched check
was done then you may lose a time slice. The window can be quite long
when signals are handled (after do_signal returned there is no reschedule
check). Without signals it is only a few instructions window.

I have not checked if it really is a problem in practice though. With
lots of signals it may be a problem.

-Andi

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