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

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Message-ID: <20080421194359.GD8770@elte.hu>
Date:	Mon, 21 Apr 2008 21:43:59 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Frans Pop <elendil@...net.nl>
Cc:	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>,
	Richard Jonsson <richie@...erworld.net>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [git pull] scheduler changes for v2.6.26


* Frans Pop <elendil@...net.nl> wrote:

> > It would be nice if you could try sched-devel/latest because it has 
> > an improved ftrace "sched_switch" tracer where you can generate much 
> > longer traces of this incident. Try the new /debug/trace_entries 
> > runtime tunable.
> 
> I'll try to get the trace and will reply on the private thread we had. 
> I may need additional instructions though.

you could also reply to this thread if you dont mind, so that others can 
chime in too.

the 700-800 msecs of delays you see are very "brutal" so there must be 
something fundamentally wrong going on here.

Could you first check (under sched-devel/latest) the quality of your 
sched-clock, via running this script:

   http://people.redhat.com/mingo/cfs-scheduler/tools/watch-rq-clock.sh

if you run it, it should output ~1000 msecs periods every second:

 europe:~> watch-rq-clock.sh
 1002.115042
 1005.509851
 1004.187275
 1004.409980
 1004.430264
 1004.445508

if it's way too 'slow', say it only 100 msecs per second, then the 
scheduler clock is mis-measuring time and what the scheduler thinks to 
be a 40 msecs delay might become a 400 msecs delay.

	Ingo
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