linux-kernel - Re: [git pull] scheduler fixes

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Date:	Sat, 17 Jan 2009 13:19:12 +0100
From:	Mike Galbraith <efault@....de>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [git pull] scheduler fixes

On Sat, 2009-01-17 at 13:00 +0100, Peter Zijlstra wrote:
> On Sat, 2009-01-17 at 11:34 +0100, Mike Galbraith wrote:
> > > Right, how about we flip the 'initial' case in place_entity() for !
> > > nr_exclusive wakeups.
> > 
> > Wouldn't that be more drastic than sleep denial?
> 
> Strictly speaking that DEBIT thing is valid for each wakeup, IIRC we
> restricted it to clone() only because that was where we could actually
> observe these latency spikes using a fork-bomb.
> 
> This reduces the latency hits to around 400ms, which is about right for
> the given load.
> 
> ---
> diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> index f34cf42..d344605 100644
> --- a/kernel/sched_fair.c
> +++ b/kernel/sched_fair.c
> @@ -671,7 +671,8 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
>  	 * little, place the new task so that it fits in the slot that
>  	 * stays open at the end.
>  	 */
> -	if (initial && sched_feat(START_DEBIT))
> +	if ((initial && sched_feat(START_DEBIT)) ||
> +			(!initial && sched_feat(WAKER_DEBIT)))
>  		vruntime += sched_vslice(cfs_rq, se);
>  
>  	if (!initial) {
> diff --git a/kernel/sched_features.h b/kernel/sched_features.h
> index 4569bfa..b5fddf0 100644
> --- a/kernel/sched_features.h
> +++ b/kernel/sched_features.h
> @@ -1,4 +1,4 @@
> -SCHED_FEAT(NEW_FAIR_SLEEPERS, 1)
> +SCHED_FEAT(NEW_FAIR_SLEEPERS, 0)
>  SCHED_FEAT(NORMALIZED_SLEEPER, 0)
>  SCHED_FEAT(ADAPTIVE_GRAN, 1)
>  SCHED_FEAT(WAKEUP_PREEMPT, 1)
> @@ -15,3 +15,4 @@ SCHED_FEAT(ASYM_EFF_LOAD, 1)
>  SCHED_FEAT(WAKEUP_OVERLAP, 0)
>  SCHED_FEAT(LAST_BUDDY, 1)
>  SCHED_FEAT(OWNER_SPIN, 1)
> +SCHED_FEAT(WAKER_DEBIT, 1)

Ouch, that doesn't look like it will be nice at all for interactivity.

(which btw was terrible with my hackery, even with booboos fixed)

	-Mike

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