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

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Message-ID: <4D52F526.5060101@gmail.com>
Date:	Wed, 09 Feb 2011 13:12:22 -0700
From:	David Ahern <dsahern@...il.com>
To:	Jeff Moyer <jmoyer@...hat.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



On 02/09/11 11:22, Jeff Moyer wrote:
> 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/*?

target_{pid,tid} are initialized to -1 in builtin-record.c I believe the
tid version is making its way through the event__synthesize_xxx code
(event__synthesize_thread -> __event__synthesize_thread ->
event__synthesize_comm and event__synthesize_mmap_events).

> 
> 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.

cpu-clock is handled through hrtimers if that helps understand the lockup.

David

> 
> Cheers,
> Jeff
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