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

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Date:	Tue, 20 Jan 2009 17:06:13 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Kevin Shanahan <kmshanah@...b.org.au>
Cc:	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>,
	Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	bugme-daemon@...zilla.kernel.org
Subject: Re: [Bug #12465] KVM guests stalling on 2.6.28 (bisected)


* Kevin Shanahan <kmshanah@...b.org.au> wrote:

> I've uploaded the debug info here:
>   http://disenchant.net/tmp/bug-12465/

one interesting number to watch for is the KVM thread's wait_max in 
/proc/*/sched. The largest one seems to be 11 milliseconds:

se.wait_max                        :             3.175034
se.wait_max                        :             4.029938
se.wait_max                        :             4.217674
se.wait_max                        :             4.957836
se.wait_max                        :            10.339471
se.wait_max                        :            11.603943

which would be about right given your latency settings:

 /proc/sys/kernel/sched_latency_ns:
 60000000

[ 60 msecs ]

but ... i dont specifically see the kvm threads there. Are they not in 
/proc/*? Maybe it's in threads and it needs to be accessed via 
/proc/*/task/*/sched, as via:

$ grep -h wait_max /proc/*/task/*/sched | sort -t: -n -k 2 | tail -10
se.wait_max                        :            77.858092
se.wait_max                        :            78.778409
se.wait_max                        :            79.379026
se.wait_max                        :            85.930963
se.wait_max                        :            87.671842
se.wait_max                        :            88.008602
se.wait_max                        :            95.095744
se.wait_max                        :           157.882573
se.wait_max                        :           268.714775
se.wait_max                        :           393.085252

so the worst-case latency

Btw., there's a few weird stats in your logs:

se.wait_max                        :          -284.864857
se.wait_max                        :          -284.843431
se.wait_max                        :          -284.820204
se.wait_max                        :          -284.345294
se.wait_max                        :          -284.298462
se.wait_max                        :          -284.018644
se.wait_max                        :          -284.018070
se.wait_max                        :          -188.022417
se.wait_max                        :          -188.021659
se.wait_max                        :           -92.030204
se.wait_max                        :           -92.027877

that field is not supposed to be negative. Mike, Peter, any ideas?

	Ingo
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