linux-kernel - Re: KVM: Softlockups in guests while running kernbench

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Date:	Fri, 11 May 2012 12:08:01 +0530
From:	Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	Andrea Arcangeli <aarcange@...hat.com>, KVM <kvm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: KVM: Softlockups in guests while running kernbench

On Thu, 10 May 2012 20:16:26 +0530, Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com> wrote:
> On Thu, 10 May 2012 15:39:04 +0530, Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com> wrote:
> 
> I had a discussion with Avi on IRC, he suggested running a trace on the
> host for the sched: tracepoints
> 
> So when I see the console of the guest, i can see the soft-lockup
> messages. When I start tracing, soft-lockups disappear. 
> 
> Kernbench is started from the host; ps output:
> 13359 pts/1    S+     0:00 perf stat -a -- ssh root@....168.123.11 cd /root/linux-src; kernbench -f -M -H -o 16 > /root/kbench.log
> 13362 pts/1    S+     0:00 ssh root@....168.123.11 cd /root/linux-src; kernbench -f -M -H -o 16 > /root/kbench.log
> 13373 pts/1    S+     0:00 perf stat -a -- ssh root@....168.123.12 cd /root/linux-src; kernbench -f -M -H -o 16 > /root/kbench.log
> 13376 pts/1    S+     0:00 ssh root@....168.123.12 cd /root/linux-src; kernbench -f -M -H -o 16 > /root/kbench.log
> 13387 pts/1    S+     0:00 perf stat -a -- ssh root@....168.123.13 cd /root/linux-src; kernbench -f -M -H -o 16 > /root/kbench.log
> 13390 pts/1    S+     0:00 ssh root@....168.123.13 cd /root/linux-src; kernbench -f -M -H -o 16 > /root/kbench.log
> 13401 pts/1    S+     0:00 perf stat -a -- ssh root@....168.123.14 cd /root/linux-src; kernbench -f -M -H -o 16 > /root/kbench.log
> 13402 pts/1    S+     0:00 ssh root@....168.123.14 cd /root/linux-src; kernbench -f -M -H -o 16 > /root/kbench.log
> 
> I have tried following commands trace-cmd:
> 1) trace-cmd record -e kvm -e sched -b 100000  -p 13362
> 2) trace-cmd record -e sched -b 100000  -p 13362
> 3) trace-cmd record -e kvm -b 100000  -p 13362
> 
> I have tried trace-cmd on qemu pid as well, I see similar behaviour in
> that case.
> 
> Peterz/Ingo, Any clue on debugging this would help.
>
With CONFIG_DEBUG_SPINLOCK=y in guest config, I stop seeing the
soft-lockup

Nikunj

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