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 e03be08d0ddff5c2a55d6af7b8de53c683961804..a0a6987fabc4d05ad92cf443be0e0a2a97ed8327 100644 (file)
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -5602,6 +5602,10 @@ static enum hrtimer_restart perf_swevent_hrtimer(struct hrtimer *hrtimer)
        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 @@ static void perf_swevent_start_hrtimer(struct perf_event *event)
        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_cancel_hrtimer(struct perf_event *event)
        }
 }
 
+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 @@ static int cpu_clock_event_init(struct perf_event *event)
        if (event->attr.config != PERF_COUNT_SW_CPU_CLOCK)
                return -ENOENT;
 
+       perf_swevent_init_hrtimer(event);
+
        return 0;
 }
 
@@ -5787,6 +5814,8 @@ static int task_clock_event_init(struct perf_event *event)
        if (event->attr.config != PERF_COUNT_SW_TASK_CLOCK)
                return -ENOENT;
 
+       perf_swevent_init_hrtimer(event);
+
        return 0;
 }