perf sched: Add option to merge like comms to lat output

perf sched: Add option to merge like comms to lat output

Sometimes when debugging large multi-threaded applications it is helpful
to collate all of the latency numbers into one bulk record to get an
idea of what is going on.

This patch does this by merging any entries that belong to the same comm
into one entry and then spits out those totals.

I've also slightly changed the output so you can see how many threads
were merged in the processing.  Here is the new default output format

 -----------------------------------------------------------------------------------------------------------
  Task                 | Runtime ms  | Switches | Average delay ms | Maximum delay ms | Maximum delay at    |
 -----------------------------------------------------------------------------------------------------------
  chrome:(23)          |  740.878 ms |     2612 | avg:    0.022 ms | max:    0.845 ms | max at: 7935.254223 s
  pulseaudio:1523      |   94.440 ms |      597 | avg:    0.027 ms | max:    0.110 ms | max at: 7934.668372 s
  threaded-ml:6042     |   72.554 ms |      386 | avg:    0.035 ms | max:    1.186 ms | max at: 7935.330911 s
  Chrome_IOThread:3832 |   52.388 ms |      456 | avg:    0.021 ms | max:    1.365 ms | max at: 7935.330602 s
  Chrome_ChildIOT:(7)  |   50.694 ms |      743 | avg:    0.021 ms | max:    1.448 ms | max at: 7935.256659 s
  Compositor:5510      |   30.012 ms |      192 | avg:    0.019 ms | max:    0.131 ms | max at: 7936.636815 s
  plugin_audio_th:6043 |   24.828 ms |      314 | avg:    0.018 ms | max:    0.143 ms | max at: 7936.205994 s
  CompositorTileW:(2)  |   14.099 ms |       45 | avg:    0.022 ms | max:    0.153 ms | max at: 7937.521800 s

the (#) after the task is the number of tasks merged, and then if there were
no tasks merged it just shows the pid.  Here is the same trace file with the -p
option to print the per-pid latency numbers

 -----------------------------------------------------------------------------------------------------------
  Task                 | Runtime ms  | Switches | Average delay ms | Maximum delay ms | Maximum delay at    |
 -----------------------------------------------------------------------------------------------------------
  chrome:5500          |  386.872 ms |      387 | avg:    0.023 ms | max:    0.241 ms | max at: 7936.001694 s
  pulseaudio:1523      |   94.440 ms |      597 | avg:    0.027 ms | max:    0.110 ms | max at: 7934.668372 s
  threaded-ml:6042     |   72.554 ms |      386 | avg:    0.035 ms | max:    1.186 ms | max at: 7935.330911 s
  chrome:10226         |   69.710 ms |      251 | avg:    0.023 ms | max:    0.764 ms | max at: 7935.992305 s
  chrome:4267          |   64.551 ms |      418 | avg:    0.021 ms | max:    0.294 ms | max at: 7937.862427 s
  chrome:4827          |   62.268 ms |       54 | avg:    0.029 ms | max:    0.666 ms | max at: 7935.992813 s
  Chrome_IOThread:3832 |   52.388 ms |      456 | avg:    0.021 ms | max:    1.365 ms | max at: 7935.330602 s
  chrome:3776          |   46.150 ms |      349 | avg:    0.023 ms | max:    0.845 ms | max at: 7935.254223 s

Signed-off-by: Josef Bacik <jbacik@fb.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: kernel-team@fb.com
Link: http://lkml.kernel.org/r/1432300720-30478-1-git-send-email-jbacik@fb.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>