linux-kernel - Re: [performance bug] volanomark regression on 37-rc1

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Date:	Tue, 16 Nov 2010 11:27:18 -0800
From:	Nikhil Rao <ncrao@...gle.com>
To:	Mike Galbraith <efault@....de>
Cc:	Rakib Mullick <rakib.mullick@...il.com>,
	"Alex,Shi" <alex.shi@...el.com>, a.p.zijlstra@...llo.nl,
	mingo@...e.hu, linux-kernel@...r.kernel.org,
	"Chen, Tim C" <tim.c.chen@...el.com>, zheng.z.yan@...el.com
Subject: Re: [performance bug] volanomark regression on 37-rc1

On Tue, Nov 16, 2010 at 9:32 AM, Mike Galbraith <efault@....de> wrote:
> On Tue, 2010-11-16 at 08:31 -0800, Nikhil Rao wrote:
>> On Tue, Nov 16, 2010 at 7:26 AM, Mike Galbraith <efault@....de> wrote:
>> > On Tue, 2010-11-16 at 20:38 +0600, Rakib Mullick wrote:
>> >
>> >> Does VolanoMark is used for scheduler benchmarking? If I'm not wrong,
>> >> I don't think it directly relates to scheduler benchmarking.
>> >
>> > It's not generally considered to be a wonderful benchmark, but it is a
>> > good indicator, and worth keeping an eye on IMHO.
>> >
>> > I don't recall whether that patch works with the idle testcase without
>> > resetting the throttle, or if it's only a bit less effective.  If it's
>> > only a little less effective, I'd be inclined to just whack the reset as
>> > Alex did.  Whatever is done has to prevent high frequency balancing.
>> >
>>
>> >From what I recall, I think removing the reset makes the original
>> patch a little less effective. I agree that we can remove the reset if
>> it hurts high frequency balancing.
>
> Ok, let's do that.  I added your ack, OK?
>

Yes, thanks for the patch.

> From: Alex Shi <alex.shi@...el.com>
> Date: Tue, 16 Nov 2010 17:34:02 +0800
>
>    sched: volanomark regression fix
>
>    Commit fab4762 triggers excessive idle balancing, causing a ~30% loss in
>    volanomark throughput.  Remove idle balancing throttle reset.
>
>    Signed-off-by: Mike Galbraith <efault@....de>
>    Acked-by: Nikhil Rao <ncrao@...gle.com>
>    Reported-by: Alex Shi <alex.shi@...el.com>
>    Cc: Ingo Molnar <mingo@...e.hu>
>    Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
>    LKML-Reference: <new-submission>
>
> ---
>  kernel/sched_fair.c |    4 ----
>  1 file changed, 4 deletions(-)
>
> Index: linux-2.6/kernel/sched_fair.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched_fair.c
> +++ linux-2.6/kernel/sched_fair.c
> @@ -1758,10 +1758,6 @@ static void pull_task(struct rq *src_rq,
>        set_task_cpu(p, this_cpu);
>        activate_task(this_rq, p, 0);
>        check_preempt_curr(this_rq, p, 0);
> -
> -       /* re-arm NEWIDLE balancing when moving tasks */
> -       src_rq->avg_idle = this_rq->avg_idle = 2*sysctl_sched_migration_cost;
> -       this_rq->idle_stamp = 0;
>  }
>
>  /*
>
>
>
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