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Subject: Re: bisected: 'perf top' causing soft lockups under Xen
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Steven Noonan <steven@uplinklabs.net>
Cc: linux-kernel@vger.kernel.org, Paul Mackerras <paulus@samba.org>,
        Ingo Molnar <mingo@elte.hu>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
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        Jeremy Fitzhardinge <jeremy@goop.org>
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Date: Fri, 10 Feb 2012 18:28:21 +0100
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On Thu, 2012-02-09 at 18:32 -0800, Steven Noonan wrote:
> [   88.517599]  [<ffffffff81085a86>] smp_call_function_single+0xec/0xfd

This looks like its waiting for an IPI to complete.. 

There's no actual BUGS or WARNs in the output, just the soft lockup
thing saying things are taking a bit of time (clearly 15s waiting for an
IPI isn't quite normal).

I've no idea why this wouldn't work on Xen, nor do the trace have any
Xen specific muck in them.