Re: [PATCH] kernel <linux-2.6.11.10> kernel/sched.c

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On Fri, 20 May 2005 17:21, Nick Piggin wrote:
> chen Shang wrote:
> >I minimized my patch and against to 2.6.12-rc4 this time, see below.
> >
> >The new schedstat fields are for the test propose only, so I removed
> >them completedly from patch. Theoritically, requeue_task() is always
> >cheaper than dequeue_task() followed by enqueue_task(). So, if 99% of
> >priority recalculation trigger requeue_task(), it will save.
> >
> >In addition, my load is to build the kernel, which took around 30
> >minutes with around 30% CPU usage on 2x2 processors (duel processors
> >with HT enable).
> >Here is the statistics:
> >
> >CPU0: priority_changed (669 times), priority_unchanged(335,138 times)
> >CPU1: priority_changed (784 times), priority_unchanged(342,419 times)
> >CPU2: priority_changed (782 times), priority_unchanged(283,494 times)
> >CPU3: priority_changed (872 times), priority_unchanged(365,865 times)
>
> OK that gives you a good grounds to look at the patch, but _performance_
> improvement is what is needed to get it included.

If you end up using requeue_task() in the fast path and it is hit frequently 
with your code you'll need to modify requeue_task to be inline as well. 
Currently it is hit only via sched_yield and once every 10 scheduler ticks 
which is why it is not inline. The performance hit will be demonstrable if it 
is hit in every schedule()

Cheers,
Con

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