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Date: Tue, 10 Dec 2013 16:32:01 -0500
From: Dave Jones <davej@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Darren Hart <dvhart@linux.intel.com>, Oleg Nesterov <oleg@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>, Mel Gorman <mgorman@suse.de>
Subject: Re: process 'stuck' at exit.
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On Tue, Dec 10, 2013 at 01:18:20PM -0800, Linus Torvalds wrote:
 > On Tue, Dec 10, 2013 at 1:06 PM, Darren Hart <dvhart@linux.intel.com> wrote:
 > >
 > >    . Knowing exactly what syscall was made would
 > > be very useful, but I don't know if that information is even available
 > > anymore.
 > 
 > Well, the loop should be visible in the profile, since it's still active.
 > 
 > So doing something like
 > 
 >      perf record -e cycles:pp -g -a sleep 60
 > 
 > to get a good profile for a minute, and then looking at the
 > instruction-level profiles in futex_requeue() should be possible.
 > 
 > Of course, inlining etc often makes those rather hard to see, and the
 > bulk of the profile is clearly all about the lock debugging overhead,
 > but if the loop is in futex_requeue() then that *should* be visible in
 > the profile, even if it may not be anywhere near the top..
 > 
 > Dave?

http://www.codemonkey.org.uk/junk/perf.data.xz

	Dave