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Commit 163ec435 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

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: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 4979d272

include/linux/perf_event.h

+4 −0
Original line number Diff line number Diff line
@@ -1110,6 +1110,10 @@ extern int sysctl_perf_event_paranoid; 
extern int sysctl_perf_event_mlock;

extern int sysctl_perf_event_sample_rate;



extern int perf_proc_update_handler(struct ctl_table *table, int write,

		void __user *buffer, size_t *lenp,

		loff_t *ppos);



static inline bool perf_paranoid_tracepoint_raw(void)

{

	return sysctl_perf_event_paranoid > -1;

kernel/perf_event.c

+24 −19
Original line number Diff line number Diff line
@@ -150,7 +150,24 @@ int sysctl_perf_event_mlock __read_mostly = 512; /* 'free' kb per user */ 
/*

 * max perf event sample rate

 */

int sysctl_perf_event_sample_rate __read_mostly = 100000;

#define DEFAULT_MAX_SAMPLE_RATE 100000

int sysctl_perf_event_sample_rate __read_mostly = DEFAULT_MAX_SAMPLE_RATE;

static int max_samples_per_tick __read_mostly =

	DIV_ROUND_UP(DEFAULT_MAX_SAMPLE_RATE, HZ);



int perf_proc_update_handler(struct ctl_table *table, int write,

		void __user *buffer, size_t *lenp,

		loff_t *ppos)

{

	int ret = proc_dointvec(table, write, buffer, lenp, ppos);



	if (ret || !write)

		return ret;



	max_samples_per_tick = DIV_ROUND_UP(sysctl_perf_event_sample_rate, HZ);



	return 0;

}



static atomic64_t perf_event_id;
@@ -4941,26 +4958,14 @@ static int __perf_event_overflow(struct perf_event *event, int nmi, 
	if (unlikely(!is_sampling_event(event)))

		return 0;



	if (!throttle) {

		hwc->interrupts++;

	} else {

		if (hwc->interrupts != MAX_INTERRUPTS) {

			hwc->interrupts++;

			if (HZ * hwc->interrupts >

					(u64)sysctl_perf_event_sample_rate) {

	if (unlikely(hwc->interrupts >= max_samples_per_tick)) {

		if (throttle) {

			hwc->interrupts = MAX_INTERRUPTS;

			perf_log_throttle(event, 0);

			ret = 1;

		}

		} else {

			/*

			 * Keep re-disabling events even though on the previous

			 * pass we disabled it - just in case we raced with a

			 * sched-in and the event got enabled again:

			 */

			ret = 1;

		}

	}

	} else

		hwc->interrupts++;



	if (event->attr.freq) {

		u64 now = perf_clock();

kernel/sysctl.c

+1 −1
Original line number Diff line number Diff line
@@ -948,7 +948,7 @@ static struct ctl_table kern_table[] = { 
		.data		= &sysctl_perf_event_sample_rate,

		.maxlen		= sizeof(sysctl_perf_event_sample_rate),

		.mode		= 0644,

		.proc_handler	= proc_dointvec,

		.proc_handler	= perf_proc_update_handler,

	},

#endif

#ifdef CONFIG_KMEMCHECK