perf: Optimize hrtimer events
There is no need to re-initialize the hrtimer every time we start it,
so don't do that (shaves a few cycles). Also, since we know hrtimers
run at a fixed rate (nanoseconds) we can pre-compute the desired
frequency at which they tick. This avoids us having to go through the
whole adaptive frequency feedback logic (shaves another few cycles).
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1297448589.5226.47.camel@laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index e03be08..a0a6987 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -5602,6 +5602,10 @@
u64 period;
event = container_of(hrtimer, struct perf_event, hw.hrtimer);
+
+ if (event->state != PERF_EVENT_STATE_ACTIVE)
+ return HRTIMER_NORESTART;
+
event->pmu->read(event);
perf_sample_data_init(&data, 0);
@@ -5628,9 +5632,6 @@
if (!is_sampling_event(event))
return;
- hrtimer_init(&hwc->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
- hwc->hrtimer.function = perf_swevent_hrtimer;
-
period = local64_read(&hwc->period_left);
if (period) {
if (period < 0)
@@ -5657,6 +5658,30 @@
}
}
+static void perf_swevent_init_hrtimer(struct perf_event *event)
+{
+ struct hw_perf_event *hwc = &event->hw;
+
+ if (!is_sampling_event(event))
+ return;
+
+ hrtimer_init(&hwc->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+ hwc->hrtimer.function = perf_swevent_hrtimer;
+
+ /*
+ * Since hrtimers have a fixed rate, we can do a static freq->period
+ * mapping and avoid the whole period adjust feedback stuff.
+ */
+ if (event->attr.freq) {
+ long freq = event->attr.sample_freq;
+
+ event->attr.sample_period = NSEC_PER_SEC / freq;
+ hwc->sample_period = event->attr.sample_period;
+ local64_set(&hwc->period_left, hwc->sample_period);
+ event->attr.freq = 0;
+ }
+}
+
/*
* Software event: cpu wall time clock
*/
@@ -5709,6 +5734,8 @@
if (event->attr.config != PERF_COUNT_SW_CPU_CLOCK)
return -ENOENT;
+ perf_swevent_init_hrtimer(event);
+
return 0;
}
@@ -5787,6 +5814,8 @@
if (event->attr.config != PERF_COUNT_SW_TASK_CLOCK)
return -ENOENT;
+ perf_swevent_init_hrtimer(event);
+
return 0;
}
