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tracing: Allow to disable cmdline recording

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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: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4C2D57F4.2050204@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Li Zefan
2010-07-02 11:07:32 +08:00
committed by Steven Rostedt
parent cc5edb0eb9
commit e870e9a124
4 changed files with 41 additions and 5 deletions
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6
kernel/trace/trace.c
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@@ -344,7 +344,7 @@ static DECLARE_WAIT_QUEUE_HEAD(trace_wait);
/* trace_flags holds trace_options default values */
unsigned long trace_flags = TRACE_ITER_PRINT_PARENT | TRACE_ITER_PRINTK |
TRACE_ITER_ANNOTATE | TRACE_ITER_CONTEXT_INFO | TRACE_ITER_SLEEP_TIME |
TRACE_ITER_GRAPH_TIME;
TRACE_ITER_GRAPH_TIME | TRACE_ITER_RECORD_CMD;
static int trace_stop_count;
static DEFINE_SPINLOCK(tracing_start_lock);
@@ -428,6 +428,7 @@ static const char *trace_options[] = {
"latency-format",
"sleep-time",
"graph-time",
"record-cmd",
NULL
};
@@ -2561,6 +2562,9 @@ static void set_tracer_flags(unsigned int mask, int enabled)
trace_flags |= mask;
else
trace_flags &= ~mask;
if (mask == TRACE_ITER_RECORD_CMD)
trace_event_enable_cmd_record(enabled);
}
static ssize_t