linux-kernel - Re: [git] CFS-devel, latest code

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Message-Id: <1190727317.11260.8.camel@Homer.simpson.net>
Date:	Tue, 25 Sep 2007 15:35:17 +0200
From:	Mike Galbraith <efault@....de>
To:	vatsa@...ux.vnet.ibm.com
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [git] CFS-devel, latest code

On Tue, 2007-09-25 at 18:21 +0530, Srivatsa Vaddagiri wrote:
> On Tue, Sep 25, 2007 at 12:36:17PM +0200, Ingo Molnar wrote:
> > hm. perhaps this fixup in kernel/sched.c:set_task_cpu():
> > 
> >         p->se.vruntime -= old_rq->cfs.min_vruntime - new_rq->cfs.min_vruntime;
> 
> This definitely does need some fixup, even though I am not sure yet if
> it will solve completely the latency issue.
> 
> I tried the following patch. I *think* I see some improvement, wrt
> latency seen when I type on the shell. Before this patch, I noticed
> oddities like "kill -9 chew-max-pid" wont kill chew-max (it is queued in
> runqueue waiting for a looong time to run before it can acknowledge
> signal and exit). With this patch, I don't see such oddities ..So I am hoping 
> it fixes the latency problem you are seeing as well.

http://lkml.org/lkml/2007/9/25/117 plus the below seems to be the SIlver
Bullet for the latencies I was seeing.

> Index: current/kernel/sched.c
> ===================================================================
> --- current.orig/kernel/sched.c
> +++ current/kernel/sched.c
> @@ -1039,6 +1039,8 @@ void set_task_cpu(struct task_struct *p,
>  {
>  	int old_cpu = task_cpu(p);
>  	struct rq *old_rq = cpu_rq(old_cpu), *new_rq = cpu_rq(new_cpu);
> +	struct cfs_rq *old_cfsrq = task_cfs_rq(p),
> +		      *new_cfsrq = cpu_cfs_rq(old_cfsrq, new_cpu);
>  	u64 clock_offset;
>  
>  	clock_offset = old_rq->clock - new_rq->clock;
> @@ -1051,7 +1053,8 @@ void set_task_cpu(struct task_struct *p,
>  	if (p->se.block_start)
>  		p->se.block_start -= clock_offset;
>  #endif
> -	p->se.vruntime -= old_rq->cfs.min_vruntime - new_rq->cfs.min_vruntime;
> +	p->se.vruntime -= old_cfsrq->min_vruntime -
> +					 new_cfsrq->min_vruntime;
>  
>  	__set_task_cpu(p, new_cpu);
>  }
>  
> 
> --
> Regards,
> vatsa

-
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