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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
Download Patch File Download Diff File Expand all files Collapse all files
kernel/trace/trace_events.c
+28 -2
View File
@@ -170,6 +170,26 @@ int ftrace_event_reg(struct ftrace_event_call *call, enum trace_reg type)
}
EXPORT_SYMBOL_GPL(ftrace_event_reg);
void trace_event_enable_cmd_record(bool enable)
{
struct ftrace_event_call *call;
mutex_lock(&event_mutex);
list_for_each_entry(call, &ftrace_events, list) {
if (!(call->flags & TRACE_EVENT_FL_ENABLED))
continue;
if (enable) {
tracing_start_cmdline_record();
call->flags |= TRACE_EVENT_FL_RECORDED_CMD;
} else {
tracing_stop_cmdline_record();
call->flags &= ~TRACE_EVENT_FL_RECORDED_CMD;
}
}
mutex_unlock(&event_mutex);
}
static int ftrace_event_enable_disable(struct ftrace_event_call *call,
int enable)
{
@@ -179,13 +199,19 @@ static int ftrace_event_enable_disable(struct ftrace_event_call *call,
case 0:
if (call->flags & TRACE_EVENT_FL_ENABLED) {
call->flags &= ~TRACE_EVENT_FL_ENABLED;
tracing_stop_cmdline_record();
if (call->flags & TRACE_EVENT_FL_RECORDED_CMD) {
tracing_stop_cmdline_record();
call->flags &= ~TRACE_EVENT_FL_RECORDED_CMD;
}
call->class->reg(call, TRACE_REG_UNREGISTER);
}
break;
case 1:
if (!(call->flags & TRACE_EVENT_FL_ENABLED)) {
tracing_start_cmdline_record();
if (trace_flags & TRACE_ITER_RECORD_CMD) {
tracing_start_cmdline_record();
call->flags |= TRACE_EVENT_FL_RECORDED_CMD;
}
ret = call->class->reg(call, TRACE_REG_REGISTER);
if (ret) {
tracing_stop_cmdline_record();