linux-kernel - Re: perf on 2.6.38-rc4 wedges my box

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Message-ID: <x49fwrxax02.fsf@segfault.boston.devel.redhat.com>
Date:	Wed, 09 Feb 2011 13:22:37 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	David Ahern <dsahern@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: perf on 2.6.38-rc4 wedges my box

David Ahern <dsahern@...il.com> writes:

> Have you tried '-e cpu-clock' for S/W based profiling vs the default H/W
> profiling? Add -v to see if the fallback to S/W is happening now.

Thanks for the suggestion, David.  I tried:

# perf record -v ls
  Warning:  ... trying to fall back to cpu-clock-ticks

couldn't open /proc/-1/status
couldn't open /proc/-1/maps
[ls output]
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.008 MB perf.data (~363 samples) ]

If I explicitly set '-e cpu-clock', then the output is the same,
except that the warning is gone.  What's up with the /proc/-1/*?

Now, when running perf record -e cpu-clock on the aio-stress run,
unsurprisingly, I get the same result:

# perf record -e cpu-clock -v -- ./aio-stress -O -o 0 -r 4 -d 32 -b 16 /dev/sds
couldn't open /proc/-1/status
couldn't open /proc/-1/maps
adding stage write
starting with write
file size 1024MB, record size 4KB, depth 32, ios per iteration 8
max io_submit 16, buffer alignment set to 4KB
threads 1 files 1 contexts 1 context offset 2MB verification off
adding file /dev/sds thread 0

and there it sits.  In this case, however, I did not see the NOHZ
warnings on the console, and this time the machine is still responding
to ping, but nothing else.

Cheers,
Jeff
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