linux-kernel - Re: [Bug #12465] KVM guests stalling on 2.6.28 (bisected)

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Message-ID: <20090120150408.GD21931@elte.hu>
Date:	Tue, 20 Jan 2009 16:04:08 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Kevin Shanahan <kmshanah@...b.org.au>, Avi Kivity <avi@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Kevin Shanahan <kmshanah@...xo.wumi.org.au>,
	Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frédéric Weisbecker <fweisbec@...il.com>
Subject: Re: [Bug #12465] KVM guests stalling on 2.6.28 (bisected)


* Steven Rostedt <rostedt@...dmis.org> wrote:

> On Tue, 20 Jan 2009, Ingo Molnar wrote:
> > Another test would be to build the scheduler latency tracer into your 
> > kernel:
> > 
> >     CONFIG_SCHED_TRACER=y
> > 
> > And enable it via:
> > 
> >     echo wakeup > /debug/tracing/current_tracer
> > 
> > and you should be seeing the worst-case scheduling latency traces in 
> > /debug/tracing/trace, and the largest observed latency will be in 
> > /debug/tracing/tracing_max_latency [in microseconds].
> 
> Note, the wakeup latency only tests realtime threads, since other 
> threads can have other issues for wakeup. I could change the wakeup 
> tracer as wakeup_rt, and make a new "wakeup" that tests all threads, but 
> it may be difficult to get something accurate.

hm, that's a significant regression then. The latency tracer used to 
measure the highest-prio task in the system - be that RT or non-rt.

	Ingo
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