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ftrace: Update dynamic ftrace calls only if necessary 

Currently dynamic ftrace calls are updated any time
the ftrace_ops is un/registered. If we do  this update
only when it's needed, we save lot of time for perf
system wide ftrace function sampling/counting.

The reason is that for system wide sampling/counting,
perf creates event for each cpu in the system.

Each event then registers separate copy of ftrace_ops,
which ends up in FTRACE_UPDATE_CALLS updates. On servers
with many cpus that means serious stall (240 cpus server):

Counting:
  # time ./perf stat -e ftrace:function -a sleep 1

   Performance counter stats for 'system wide':

              370,663      ftrace:function

          1.401427505 seconds time elapsed

  real    3m51.743s
  user    0m0.023s
  sys     3m48.569s

Sampling:
  # time ./perf record -e ftrace:function -a sleep 1
  [ perf record: Woken up 0 times to write data ]
  Warning:
  Processed 141200 events and lost 5 chunks!

  [ perf record: Captured and wrote 10.703 MB perf.data (135950 samples) ]

  real    2m31.429s
  user    0m0.213s
  sys     2m29.494s

There's no reason to do the FTRACE_UPDATE_CALLS update
for each event in perf case, because all the ftrace_ops
always share the same filter, so the updated calls are
always the same.

It's required that only first ftrace_ops registration
does the FTRACE_UPDATE_CALLS update (also sometimes
the second if the first one used the trampoline), but
the rest can be only cheaply linked into the ftrace_ops
list.

Counting:
  # time ./perf stat -e ftrace:function -a sleep 1

   Performance counter stats for 'system wide':

             398,571      ftrace:function

         1.377503733 seconds time elapsed

  real    0m2.787s
  user    0m0.005s
  sys     0m1.883s

Sampling:
  # time ./perf record -e ftrace:function -a sleep 1
  [ perf record: Woken up 0 times to write data ]
  Warning:
  Processed 261730 events and lost 9 chunks!

  [ perf record: Captured and wrote 19.907 MB perf.data (256293 samples) ]

  real    1m31.948s
  user    0m0.309s
  sys     1m32.051s

Link: http://lkml.kernel.org/r/1458138873-1553-6-git-send-email-jolsa@kernel.org

Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Jiri Olsa 2016-03-16 15:34:33 +01:00 committed by Steven Rostedt
parent 84b6d3e614
commit 7f50d06bb6
1 changed files with 5 additions and 5 deletions
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10
kernel/trace/ftrace.c
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@ -2651,7 +2651,6 @@ static int ftrace_startup(struct ftrace_ops *ops, int command)
return ret;
ftrace_start_up++;
command |= FTRACE_UPDATE_CALLS;
/*
* Note that ftrace probes uses this to start up
@ -2672,7 +2671,8 @@ static int ftrace_startup(struct ftrace_ops *ops, int command)
return ret;
}
ftrace_hash_rec_enable(ops, 1);
if (ftrace_hash_rec_enable(ops, 1))
command |= FTRACE_UPDATE_CALLS;
ftrace_startup_enable(command);
@ -2702,12 +2702,12 @@ static int ftrace_shutdown(struct ftrace_ops *ops, int command)
/* Disabling ipmodify never fails */
ftrace_hash_ipmodify_disable(ops);
ftrace_hash_rec_disable(ops, 1);
if (ftrace_hash_rec_disable(ops, 1))
command |= FTRACE_UPDATE_CALLS;
ops->flags &= ~FTRACE_OPS_FL_ENABLED;
command |= FTRACE_UPDATE_CALLS;
if (saved_ftrace_func != ftrace_trace_function) {
saved_ftrace_func = ftrace_trace_function;
command |= FTRACE_UPDATE_TRACE_FUNC;