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>

1 files changed, 32 insertions, 3 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index e03be08d0ddf..a0a6987fabc4 100644
--- 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;
 }