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perf: Optimize throttling code
By pre-computing the maximum number of samples per tick we can avoid a multiplication and a conditional since MAX_INTERRUPTS > max_samples_per_tick. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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@ -1110,6 +1110,10 @@ extern int sysctl_perf_event_paranoid;
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extern int sysctl_perf_event_mlock;
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extern int sysctl_perf_event_sample_rate;
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extern int perf_proc_update_handler(struct ctl_table *table, int write,
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void __user *buffer, size_t *lenp,
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loff_t *ppos);
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static inline bool perf_paranoid_tracepoint_raw(void)
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{
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return sysctl_perf_event_paranoid > -1;
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@ -150,7 +150,24 @@ int sysctl_perf_event_mlock __read_mostly = 512; /* 'free' kb per user */
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/*
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* max perf event sample rate
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*/
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int sysctl_perf_event_sample_rate __read_mostly = 100000;
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#define DEFAULT_MAX_SAMPLE_RATE 100000
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int sysctl_perf_event_sample_rate __read_mostly = DEFAULT_MAX_SAMPLE_RATE;
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static int max_samples_per_tick __read_mostly =
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DIV_ROUND_UP(DEFAULT_MAX_SAMPLE_RATE, HZ);
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int perf_proc_update_handler(struct ctl_table *table, int write,
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void __user *buffer, size_t *lenp,
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loff_t *ppos)
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{
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int ret = proc_dointvec(table, write, buffer, lenp, ppos);
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if (ret || !write)
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return ret;
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max_samples_per_tick = DIV_ROUND_UP(sysctl_perf_event_sample_rate, HZ);
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return 0;
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}
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static atomic64_t perf_event_id;
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@ -4941,26 +4958,14 @@ static int __perf_event_overflow(struct perf_event *event, int nmi,
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if (unlikely(!is_sampling_event(event)))
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return 0;
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if (!throttle) {
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hwc->interrupts++;
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} else {
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if (hwc->interrupts != MAX_INTERRUPTS) {
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hwc->interrupts++;
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if (HZ * hwc->interrupts >
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(u64)sysctl_perf_event_sample_rate) {
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hwc->interrupts = MAX_INTERRUPTS;
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perf_log_throttle(event, 0);
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ret = 1;
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}
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} else {
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/*
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* Keep re-disabling events even though on the previous
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* pass we disabled it - just in case we raced with a
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* sched-in and the event got enabled again:
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*/
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if (unlikely(hwc->interrupts >= max_samples_per_tick)) {
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if (throttle) {
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hwc->interrupts = MAX_INTERRUPTS;
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perf_log_throttle(event, 0);
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ret = 1;
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}
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}
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} else
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hwc->interrupts++;
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if (event->attr.freq) {
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u64 now = perf_clock();
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@ -948,7 +948,7 @@ static struct ctl_table kern_table[] = {
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.data = &sysctl_perf_event_sample_rate,
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.maxlen = sizeof(sysctl_perf_event_sample_rate),
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.mode = 0644,
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.proc_handler = proc_dointvec,
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.proc_handler = perf_proc_update_handler,
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},
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#endif
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#ifdef CONFIG_KMEMCHECK
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