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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>
This commit is contained in:
Peter Zijlstra 2011-02-15 12:41:46 +01:00 committed by Ingo Molnar
parent 163ec4354a
commit ba3dd36c67
1 changed files with 32 additions and 3 deletions
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35
kernel/perf_event.c
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@ -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;
}