tracing: Allow to disable cmdline recording
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>
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index e8e6043..09b4fa6 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -170,6 +170,26 @@
}
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 @@
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();