linux-kernel - Re: [git pull] scheduler changes for v2.6.26

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Date:	Tue, 22 Apr 2008 10:59:05 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mike Galbraith <efault@....de>
Cc:	Frans Pop <elendil@...net.nl>, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Richard Jonsson <richie@...erworld.net>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [git pull] scheduler changes for v2.6.26

* Mike Galbraith <efault@....de> wrote:

> > the 700-800 msecs of delays you see are very "brutal" so there must 
> > be something fundamentally wrong going on here.
> 
> I'm seeing latency hits with 26.git, whereas 25 is hit free.

ok. I think what happens is that your broken sched-clock hid the real 
breakage. Lets try fix the real breakage now.

I've uploaded a new sched-devel.git that is against very latest -git, 
could you try ftrace (with a sufficiently large 
/debug/tracing/tracing_max_entries value) - perhaps the 
worst-case-wakeup-latency tracer shows large latencies? If not, then 
maybe the sched_switch tracer gives a better insight into what's 
happening?

> Erm, should my Q6600 emit such?

on nohz it could happen - and fixed in -git. Patch looked too dangerous 
for late-2.6.25 to merge.

> On 26.git, I get numbers like yours, but with occasional dips down to 
> ~700, though the latency hits don't _seem_ to be synchronous with 
> watch-rq-clock.sh glitchies.

hm, the dips shouldnt be happening normally.

	Ingo
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