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ftrace: Initialize the ftrace profiler for each possible cpu
authorMiao Xie <miaox@cn.fujitsu.com>
Mon, 16 Dec 2013 07:20:01 +0000 (15:20 +0800)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Thu, 9 Jan 2014 20:24:20 +0000 (12:24 -0800)
commit885154cee87db097b01ae35d9ae9ee5feabeb9d7
treef134c73cdf203a4d62f7c0a42d714b53b94c2f02
parent480da400c39d5c4398765623c7bb007a359a059f
ftrace: Initialize the ftrace profiler for each possible cpu

commit c4602c1c818bd6626178d6d3fcc152d9f2f48ac0 upstream.

Ftrace currently initializes only the online CPUs. This implementation has
two problems:
- If we online a CPU after we enable the function profile, and then run the
  test, we will lose the trace information on that CPU.
  Steps to reproduce:
  # echo 0 > /sys/devices/system/cpu/cpu1/online
  # cd <debugfs>/tracing/
  # echo <some function name> >> set_ftrace_filter
  # echo 1 > function_profile_enabled
  # echo 1 > /sys/devices/system/cpu/cpu1/online
  # run test
- If we offline a CPU before we enable the function profile, we will not clear
  the trace information when we enable the function profile. It will trouble
  the users.
  Steps to reproduce:
  # cd <debugfs>/tracing/
  # echo <some function name> >> set_ftrace_filter
  # echo 1 > function_profile_enabled
  # run test
  # cat trace_stat/function*
  # echo 0 > /sys/devices/system/cpu/cpu1/online
  # echo 0 > function_profile_enabled
  # echo 1 > function_profile_enabled
  # cat trace_stat/function*
  # run test
  # cat trace_stat/function*

So it is better that we initialize the ftrace profiler for each possible cpu
every time we enable the function profile instead of just the online ones.

Link: http://lkml.kernel.org/r/1387178401-10619-1-git-send-email-miaox@cn.fujitsu.com
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
kernel/trace/ftrace.c