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.c b/kernel/trace/trace.c
index 8683dec..af90429 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -344,7 +344,7 @@
/* 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 @@
"latency-format",
"sleep-time",
"graph-time",
+ "record-cmd",
NULL
};
@@ -2561,6 +2562,9 @@
trace_flags |= mask;
else
trace_flags &= ~mask;
+
+ if (mask == TRACE_ITER_RECORD_CMD)
+ trace_event_enable_cmd_record(enabled);
}
static ssize_t
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 84d3f12..7778f06 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -591,6 +591,7 @@
TRACE_ITER_LATENCY_FMT = 0x20000,
TRACE_ITER_SLEEP_TIME = 0x40000,
TRACE_ITER_GRAPH_TIME = 0x80000,
+ TRACE_ITER_RECORD_CMD = 0x100000,
};
/*
@@ -723,6 +724,8 @@
return 0;
}
+extern void trace_event_enable_cmd_record(bool enable);
+
extern struct mutex event_mutex;
extern struct list_head ftrace_events;
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();