linux-kernel - Re: perf-stat per thread results

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Date:	Sat, 14 May 2011 12:57:00 -0600
From:	David Ahern <dsahern@...il.com>
To:	Wim Heirman <wim@...rman.net>
CC:	Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Brice Goglin <Brice.Goglin@...ia.fr>
Subject: Re: perf-stat per thread results



On 05/14/11 12:52, Wim Heirman wrote:
> 2011/5/14 David Ahern <dsahern@...il.com>:
>> On 05/14/11 06:49, Wim Heirman wrote:
>>>> Hmm.... my mileage varies using latest kernel
>>>> (446cc6345d3de6571bdd0840f48aca441488a28d)
>>>>
>>>> $ /tmp/build-perf/perf record --stat -fo /tmp/perf.data -p $(pidof rsyslogd)
>>>> ^C[ perf record: Woken up 1 times to write data ]
>>>> [ perf record: Captured and wrote 0.007 MB /tmp/perf.data (~308 samples) ]
>>>>
>>>> $ /tmp/build-perf/perf report -T -i /tmp/perf.data
>>>> # Events: 6  cycles
>>>> #
>>>> # Overhead   Command      Shared Object                      Symbol
>>>> # ........  ........  .................  ..........................
>>>> #
>>>>    97.61%  rsyslogd  libc-2.13.so       [.] __libc_disable_asynccancel
>>>>     2.39%  rsyslogd  [kernel.kallsyms]  [k] native_write_msr_safe
>>>>
>>>>
>>>> #
>>>> # (For a higher level overview, try: perf report --sort comm,dso)
>>>> #
>>>> # PID  TID
>>>>
>>>>
>>>> ie., I do not get the counter values. Specifying the counter with -e
>>>> (e.g., -e branch-misses) does not help -- still no counter output.
>>>
>>> Is rsyslogd multithreaded? (Or at least, do the non-main threads
>>> execute any work during your perf-record measurement) If not, then
>>> what you see is consistent with what I'm getting, i.e. everything but
>>> the main thread is reported.
>>
>> It is multithreaded, but my point is that I do not get counter output at
>> the end -- the PID/TID table is empty. I do not get counters for single
>> threaded processes nor for commands run by perf record -- e.g.,
>> /tmp/build-perf/perf record --stat -e instructions -fo /tmp/perf.data --
>> sleep 1
> 
> My guess was that none of the threads got scheduled while you did your
> perf-record run (rsyslogd usually isn't exactly very CPU intensive).
> And the main thread isn't ever reported, at least that's the bug I'm
> seeing. Can you try with a compute-intensive, multi-threaded program?
> 
> Wim.

The reports show data was collected. I have done a number of simple
examples -- all of which execute at least 1 instruction, but the
counters are not displayed (which they should be per the commit
changelog commit).

David
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