perf sched: Add -C option to measure on a specific CPU

perf sched: Add -C option to measure on a specific CPU

To refresh, trying to sched record only one CPU results in bogus
latencies as below.

I fixed^Wmade it stop doing the bad thing today, by
following task migration events properly.

Before:

  marge:/root/tmp # taskset -c 1 perf sched record -C 0 -- sleep 10
  marge:/root/tmp # perf sched lat
   -----------------------------------------------------------------------------------------
    Task                  |   Runtime ms  | Switches | Average delay ms | Maximum delay ms |
   -----------------------------------------------------------------------------------------
    Xorg:4943             |      1.290 ms |        1 | avg: 1670.132 ms | max: 1670.132 ms |
    hald-addon-stor:3569  |      0.091 ms |        3 | avg:  658.609 ms | max: 1975.797 ms |
    hald-addon-stor:3573  |      0.209 ms |        4 | avg:  499.138 ms | max: 1990.565 ms |
    audispd:4270          |      0.012 ms |        1 | avg:    0.015 ms | max:    0.015 ms |
  ....

  marge:/root/tmp # perf sched trace|grep 'Xorg:4943'
           swapper-0     [000]   401.184013288: sched_stat_runtime: task: Xorg:4943 runtime: 1233188 [ns], vruntime: 19105169779 [ns]
   rt2870TimerQHan-4947  [000]   402.854140127: sched_stat_wait: task: Xorg:4943 wait: 580073 [ns]
   rt2870TimerQHan-4947  [000]   402.854141770: sched_migrate_task: task Xorg:4943 [140] from: 1  to: 0
   rt2870TimerQHan-4947  [000]   402.854143854: sched_stat_wait: task: Xorg:4943 wait: 0 [ns]
   rt2870TimerQHan-4947  [000]   402.854145397: sched_switch: task rt2870TimerQHan:4947 [140] (D) ==> Xorg:4943 [140]
              Xorg-4943  [000]   402.854193133: sched_stat_runtime: task: Xorg:4943 runtime: 56546 [ns], vruntime: 11766332500 [ns]
              Xorg-4943  [000]   402.854196842: sched_switch: task Xorg:4943 [140] (S) ==> swapper:0 [140]

After:

  marge:/root/tmp # taskset -c 1 perf sched record -C 0 -- sleep 10
  marge:/root/tmp # perf sched lat
   -----------------------------------------------------------------------------------------
    Task                  |   Runtime ms  | Switches | Average delay ms | Maximum delay ms |
   -----------------------------------------------------------------------------------------
    amarokapp:11150       |    271.297 ms |      878 | avg:    0.130 ms | max:    1.057 ms |
    konsole:5965          |      1.370 ms |       12 | avg:    0.092 ms | max:    0.855 ms |
    Xorg:4943             |    179.980 ms |     1109 | avg:    0.087 ms | max:    1.206 ms |
    hald-addon-stor:3574  |      0.212 ms |        9 | avg:    0.040 ms | max:    0.169 ms |
    hald-addon-stor:3570  |      0.223 ms |        9 | avg:    0.037 ms | max:    0.223 ms |
    klauncher:5864        |      0.550 ms |        8 | avg:    0.032 ms | max:    0.048 ms |

The 'Maximum delay ms' results are now sane.

Signed-off-by: Mike Galbraith <efault@gmx.de>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>