From ba3dd36c6775264ee6e7354ba1aabcd6e86d7298 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 15 Feb 2011 12:41:46 +0100 Subject: [PATCH] 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 LKML-Reference: <1297448589.5226.47.camel@laptop> Signed-off-by: Ingo Molnar --- kernel/perf_event.c | 35 ++++++++++++++++++++++++++++++++--- 1 file 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; }