1. 21 7月, 2010 1 次提交
    • L
      tracing: Allow to disable cmdline recording · e870e9a1
      Li Zefan 提交于
      We found that even enabling a single trace event that will rarely be
      triggered can add big overhead to context switch.
      
      (lmbench context switch test)
       -------------------------------------------------
       2p/0K 2p/16K 2p/64K 8p/16K 8p/64K 16p/16K 16p/64K
       ctxsw  ctxsw  ctxsw ctxsw  ctxsw   ctxsw   ctxsw
      ------ ------ ------ ------ ------ ------- -------
        2.19   2.3   2.21   2.56   2.13     2.54    2.07
        2.39   2.51  2.35   2.75   2.27     2.81    2.24
      
      The overhead is 6% ~ 11%.
      
      It's because when a trace event is enabled 3 tracepoints (sched_switch,
      sched_wakeup, sched_wakeup_new) will be activated to map pid to cmdname.
      
      We'd like to avoid this overhead, so add a trace option '(no)record-cmd'
      to allow to disable cmdline recording.
      Signed-off-by: NLi Zefan <lizf@cn.fujitsu.com>
      LKML-Reference: <4C2D57F4.2050204@cn.fujitsu.com>
      Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>
      e870e9a1
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