linux-kernel - Re: [PATCH][RFC] Adding information of counts processes acquired how many spinlocks to schedstat

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Date:	Wed, 1 Jul 2009 09:31:39 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Hitoshi Mitake <mitake@....info.waseda.ac.jp>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Frédéric Weisbecker <fweisbec@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH][RFC] Adding information of counts processes acquired
	how many spinlocks to schedstat


* Hitoshi Mitake <mitake@....info.waseda.ac.jp> wrote:

> Hi,
> 
> I wrote a test patch which add information of counts processes 
> acquired how many spinlocks to schedstat. After applied this 
> patch, /proc/<PID>/sched will change like this,
> 
> init (1, #threads: 1)
> ---------------------------------------------------------
> se.exec_start                      :        482130.851458
> se.vruntime                        :         26883.107980
> se.sum_exec_runtime                :          2316.651816
> se.avg_overlap                     :             0.480053
> se.avg_wakeup                      :            14.999993
> ....
> se.nr_wakeups_passive              :                    1
> se.nr_wakeups_idle                 :                    0
> se.nr_acquired_spinlock            :                74483
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Looks potentially useful - but it would be nice and go one step 
further and add lock acquire stats as a software-counter.

Perfcounters is a feature of the latest upstream kernel, there's a 
(still very small) Wiki page about it at:

   http://perf.wiki.kernel.org

With perfcounters we can instrument various software properties of 
the kernel as well, for example the number of page-faults in the 
system per second:

  $ perf stat -a -e page-faults sleep 1

  Performance counter stats for 'sleep 1':

          294387  page-faults             

     1.022318527  seconds time elapsed

Now, it would be nice to have a lock-acquire software-counter as 
well, which would output things like:

  $ perf stat -a -e lock-acquires sleep 1

  Performance counter stats for 'sleep 1':

          294387  lock-acquires

     1.022318527  seconds time elapsed

Furthermore, beyond plain counts, doing this would also allow the 
profiling of lock acquire places: perf record -e lock-acquires and 
perf report would work fine.

It is really easy to add a new sw counter, check how it is done for 
the pagefault counter(s), see the uses of PERF_COUNT_SW_PAGE_FAULTS 
in the following files:

  $ git grep -l PERF_COUNT_SW_PAGE_FAULTS

  arch/powerpc/mm/fault.c
  arch/x86/mm/fault.c
  include/linux/perf_counter.h
  kernel/perf_counter.c
  tools/perf/builtin-stat.c
  tools/perf/design.txt

Would you be interested in having a look at this?

	Ingo
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