linux-kernel - Re: 2.6.24-git4+ regression

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Date:	Mon, 4 Feb 2008 12:17:47 +0100
From:	Lukas Hejtmanek <xhejtman@....muni.cz>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: 2.6.24-git4+ regression

Ingo,

any progress here? I've tried to revert this patch:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=67e9fb2a39a1d454218d50383094940982be138f

as it was marked as suspicious patch in this case
(http://www.uwsg.indiana.edu/hypermail/linux/kernel/0801.3/1665.html)

but in such a case, kernel 2.6.24-git13 does oops at startup in sched_slice.

I think this is really *big* regression in 2.6.24 kernel.

On Thu, Jan 31, 2008 at 11:29:19AM +0100, Ingo Molnar wrote:
> 
> * Lukas Hejtmanek <xhejtman@....muni.cz> wrote:
> 
> > I noticed short thread in LKM regarding "sched: add vslice" causes 
> > horrible interactivity under load.
> > 
> > I can see similar behavior. If I stress both CPU cores, even typing on 
> > keyboard suffers from huge latencies, I can see letters appearing with 
> > delay (typing into xterm). No swap is used at all, having 1GB free 
> > RAM.
> > 
> > I noticed this bad behavior with 2.6.24-git[46], 2.6.24-rc8-git was 
> > OK.
> 
> if you apply the current sched-fixes (rollup patch below), does it get 
> any better?
> 
> 	Ingo
> 
> Index: linux/kernel/sched_fair.c
> ===================================================================
> --- linux.orig/kernel/sched_fair.c
> +++ linux/kernel/sched_fair.c
> @@ -520,7 +520,7 @@ place_entity(struct cfs_rq *cfs_rq, stru
>  
>  	if (!initial) {
>  		/* sleeps upto a single latency don't count. */
> -		if (sched_feat(NEW_FAIR_SLEEPERS) && entity_is_task(se))
> +		if (sched_feat(NEW_FAIR_SLEEPERS))
>  			vruntime -= sysctl_sched_latency;
>  
>  		/* ensure we never gain time by being placed backwards. */
> @@ -1106,7 +1106,11 @@ static void check_preempt_wakeup(struct 
>  	}
>  
>  	gran = sysctl_sched_wakeup_granularity;
> -	if (unlikely(se->load.weight != NICE_0_LOAD))
> +	/*
> +	 * More easily preempt - nice tasks, while not making
> +	 * it harder for + nice tasks.
> +	 */
> +	if (unlikely(se->load.weight > NICE_0_LOAD))
>  		gran = calc_delta_fair(gran, &se->load);
>  
>  	if (pse->vruntime + gran < se->vruntime)

-- 
Lukáš Hejtmánek
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