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Subject[PATCH v4 2/2] perf: add sysfs entry to adjust multiplexing interval per PMU
Date
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.

Signed-off-by: Stephane Eranian <eranian@google.com>
---
include/linux/perf_event.h | 1 +
kernel/events/core.c | 56 ++++++++++++++++++++++++++++++++++++++++----
2 files changed, 53 insertions(+), 4 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index bb51329..bca8e25 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -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
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 3e12fc9..7c3f00f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -692,13 +692,21 @@ 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;
@@ -5998,9 +6006,49 @@ 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;
+
+ 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);
+ }
+
+ return count;
+}
+
+#define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
+
static struct device_attribute pmu_dev_attrs[] = {
- __ATTR_RO(type),
- __ATTR_NULL,
+ __ATTR_RO(type),
+ __ATTR_RW(perf_event_mux_interval_ms),
+ __ATTR_NULL,
};

static int pmu_bus_running;
--
1.7.9.5


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