Commit 62b85639 authored by Stephane Eranian's avatar Stephane Eranian Committed by Ingo Molnar
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perf: Add sysfs entry to adjust multiplexing interval per PMU 



This patch adds /sys/device/xxx/perf_event_mux_interval_ms to ajust
the multiplexing interval per PMU. The unit is milliseconds. Value has
to be >= 1.

In the 4th version, we renamed the sysfs file to be more consistent
with the other /proc/sys/kernel entries for perf_events.

In the 5th version, we handle the reprogramming of the hrtimer using
hrtimer_forward_now(). That way, we sync up to new timer value quickly
(suggested by Jiri Olsa).

Signed-off-by: default avatarStephane Eranian <eranian@google.com>
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: http://lkml.kernel.org/r/1364991694-5876-3-git-send-email-eranian@google.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 9e630205

include/linux/perf_event.h

+1 −0
Original line number Diff line number Diff line
@@ -194,6 +194,7 @@ struct pmu { 
	int * __percpu			pmu_disable_count;

	struct perf_cpu_context * __percpu pmu_cpu_context;

	int				task_ctx_nr;

	int				hrtimer_interval_ms;



	/*

	 * Fully disable/enable this PMU, can be used to protect from the PMI

kernel/events/core.c

+59 −4
Original line number Diff line number Diff line
@@ -723,13 +723,21 @@ static void __perf_cpu_hrtimer_init(struct perf_cpu_context *cpuctx, int cpu) 
{

	struct hrtimer *hr = &cpuctx->hrtimer;

	struct pmu *pmu = cpuctx->ctx.pmu;

	int timer;



	/* no multiplexing needed for SW PMU */

	if (pmu->task_ctx_nr == perf_sw_context)

		return;



	cpuctx->hrtimer_interval =

		ns_to_ktime(NSEC_PER_MSEC * PERF_CPU_HRTIMER);

	/*

	 * check default is sane, if not set then force to

	 * default interval (1/tick)

	 */

	timer = pmu->hrtimer_interval_ms;

	if (timer < 1)

		timer = pmu->hrtimer_interval_ms = PERF_CPU_HRTIMER;



	cpuctx->hrtimer_interval = ns_to_ktime(NSEC_PER_MSEC * timer);



	hrtimer_init(hr, CLOCK_MONOTONIC, HRTIMER_MODE_REL_PINNED);

	hr->function = perf_cpu_hrtimer_handler;
@@ -6001,8 +6009,55 @@ type_show(struct device *dev, struct device_attribute *attr, char *page) 
	return snprintf(page, PAGE_SIZE-1, "%d\n", pmu->type);

}



static ssize_t

perf_event_mux_interval_ms_show(struct device *dev,

				struct device_attribute *attr,

				char *page)

{

	struct pmu *pmu = dev_get_drvdata(dev);



	return snprintf(page, PAGE_SIZE-1, "%d\n", pmu->hrtimer_interval_ms);

}



static ssize_t

perf_event_mux_interval_ms_store(struct device *dev,

				 struct device_attribute *attr,

				 const char *buf, size_t count)

{

	struct pmu *pmu = dev_get_drvdata(dev);

	int timer, cpu, ret;



	ret = kstrtoint(buf, 0, &timer);

	if (ret)

		return ret;



	if (timer < 1)

		return -EINVAL;



	/* same value, noting to do */

	if (timer == pmu->hrtimer_interval_ms)

		return count;



	pmu->hrtimer_interval_ms = timer;



	/* update all cpuctx for this PMU */

	for_each_possible_cpu(cpu) {

		struct perf_cpu_context *cpuctx;

		cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu);

		cpuctx->hrtimer_interval = ns_to_ktime(NSEC_PER_MSEC * timer);



		if (hrtimer_active(&cpuctx->hrtimer))

			hrtimer_forward_now(&cpuctx->hrtimer, cpuctx->hrtimer_interval);

	}



	return count;

}



#define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)



static struct device_attribute pmu_dev_attrs[] = {

	__ATTR_RO(type),

	__ATTR_RW(perf_event_mux_interval_ms),

	__ATTR_NULL,

};

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