Commit e870e9a1 authored by Li Zefan's avatar Li Zefan Committed by Steven Rostedt
Browse files

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: default avatarLi Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4C2D57F4.2050204@cn.fujitsu.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent cc5edb0e

include/linux/ftrace_event.h

+5 −2
Original line number Diff line number Diff line
@@ -152,11 +152,13 @@ extern int ftrace_event_reg(struct ftrace_event_call *event, 
enum {

	TRACE_EVENT_FL_ENABLED_BIT,

	TRACE_EVENT_FL_FILTERED_BIT,

	TRACE_EVENT_FL_RECORDED_CMD_BIT,

};



enum {

	TRACE_EVENT_FL_ENABLED		= (1 << TRACE_EVENT_FL_ENABLED_BIT),

	TRACE_EVENT_FL_FILTERED		= (1 << TRACE_EVENT_FL_FILTERED_BIT),

	TRACE_EVENT_FL_RECORDED_CMD	= (1 << TRACE_EVENT_FL_RECORDED_CMD_BIT),

};



struct ftrace_event_call {
@@ -174,6 +176,7 @@ struct ftrace_event_call { 
	 * 32 bit flags:

	 *   bit 1:		enabled

	 *   bit 2:		filter_active

	 *   bit 3:		enabled cmd record

	 *

	 * Changes to flags must hold the event_mutex.

	 *

kernel/trace/trace.c

+5 −1
Original line number Diff line number Diff line
@@ -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

kernel/trace/trace.h

+3 −0
Original line number Diff line number Diff line
@@ -591,6 +591,7 @@ enum trace_iterator_flags { 
	TRACE_ITER_LATENCY_FMT		= 0x20000,

	TRACE_ITER_SLEEP_TIME		= 0x40000,

	TRACE_ITER_GRAPH_TIME		= 0x80000,

	TRACE_ITER_RECORD_CMD		= 0x100000,

};



/*
@@ -723,6 +724,8 @@ filter_check_discard(struct ftrace_event_call *call, void *rec, 
	return 0;

}



extern void trace_event_enable_cmd_record(bool enable);



extern struct mutex event_mutex;

extern struct list_head ftrace_events;

kernel/trace/trace_events.c

+28 −2
Original line number Diff line number Diff line
@@ -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;

			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)) {

			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();

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