diff options
author | Jiri Olsa <jolsa@kernel.org> | 2016-03-16 17:34:33 +0300 |
---|---|---|
committer | Steven Rostedt <rostedt@goodmis.org> | 2016-03-18 17:30:34 +0300 |
commit | 7f50d06bb6b825d34f069c6c7a1aab96ad0b94d9 (patch) | |
tree | 295cd485186a20733d0295cf45d7df044bbb4ac7 /kernel/trace | |
parent | 84b6d3e6149c5280bc18b42e2f12efdaf354e49c (diff) | |
download | linux-7f50d06bb6b825d34f069c6c7a1aab96ad0b94d9.tar.xz |
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/trace')
-rw-r--r-- | kernel/trace/ftrace.c | 10 |
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; |