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/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 01df7ca4ead72e19b54a853775efbda9cf6c78f2..2b7b1395b4d50864fb0246b01febb10f942ac772 100644 (file)
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -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.
         *

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8683dec6946b8d2aa8f64e0cd288de1713d72d82..af9042977c086020e3bb6cee7fadc464ca634f29 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -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

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 84d3f123e86f400ca4f4f9ee32065f8e4ade5b77..7778f067fc8bff8215ed2a124174b997e4e87200 100644 (file)
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -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;
 

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index e8e6043f4d29efdc2f475842d43ca65a7652f7e5..09b4fa6e4d3be8b83758c48a529d01a6f18010da 100644 (file)
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -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();