linux-kernel - Re: [PATCH] sched/fair: change where we report sched stats

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Date:	Thu, 11 Dec 2014 04:34:16 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Josef Bacik <jbacik@...com>
Cc:	bmaurer@...com, rkroll@...com, kernel-team@...com,
	mingo@...hat.com, peterz@...radead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/fair: change where we report sched stats

On Wed, 2014-12-10 at 16:48 -0500, Josef Bacik wrote: 
> On 12/10/2014 01:23 AM, Mike Galbraith wrote:
> > On Tue, 2014-12-09 at 13:21 -0500, Josef Bacik wrote:
> >
> >> This patch moves stat stuff to after the schedule, right as we are waking up,
> >
> > But sleep/block ends when the task is awakened/enqueued, not when it
> > gets the CPU.  You're adding scheduling latency, breaking accounting.
> >
> 
> Yes I'm aware of that.  I don't care if the delay time is slightly 
> higher than normal, I care about knowing exactly why we were sleeping to 
> begin with.  I suppose I could leave the accounting part where it is and 
> then just fire the tracepoint when it's put on the CPU so we get the 
> best of both worlds, but honestly I don't feel like adding the extra 
> scheduling latency into the accounting is that big of a deal.  Thanks,

I think sleep/iowait should remain what they are, sleep/iowait end at
wakeup.  I don't think waker trace is useless either for that matter.
Who/when ends a sleep period is just as much a part of the picture as
what triggered that sleep.  Waker scheduling latency, thumb twiddling
etc. extend sleep.

Shrug, maintainer call.  I don't recall ever having any difficulty
determining why a task went to sleep, so don't get it.

-Mike

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