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authorJiri Olsa <jolsa@kernel.org>2016-03-16 15:34:33 +0100
committerSteven Rostedt <rostedt@goodmis.org>2016-03-18 10:30:34 -0400
commit7f50d06bb6b825d34f069c6c7a1aab96ad0b94d9 (patch)
tree295cd485186a20733d0295cf45d7df044bbb4ac7 /kernel
parent84b6d3e6149c5280bc18b42e2f12efdaf354e49c (diff)
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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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/trace/ftrace.c10
1 files changed, 5 insertions, 5 deletions
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 11ffcfd3804e..d3850cbb840f 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -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);
@@ -2702,11 +2702,11 @@ 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);
- ops->flags &= ~FTRACE_OPS_FL_ENABLED;
+ if (ftrace_hash_rec_disable(ops, 1))
+ command |= FTRACE_UPDATE_CALLS;
- command |= FTRACE_UPDATE_CALLS;
+ ops->flags &= ~FTRACE_OPS_FL_ENABLED;
if (saved_ftrace_func != ftrace_trace_function) {
saved_ftrace_func = ftrace_trace_function;