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

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Message-ID: <alpine.DEB.1.10.0901200957220.2681@gandalf.stny.rr.com>
Date:	Tue, 20 Jan 2009 09:59:01 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
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)



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.

-- Steve
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