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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>
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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
include/linux/ftrace_event.h
View File

@ -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_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.
*

6
kernel/trace/trace.c
View File

@ -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

3
kernel/trace/trace.h
View File

@ -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;

30
kernel/trace/trace_events.c
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();