Re: lowish-latency patch for 2.4.0-test9

[Andi Kleen]

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