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Date: Sat, 07 Jan 2012 18:03:38 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Stephane Eranian <eranian@...gle.com>
Cc: linux-kernel@...r.kernel.org, gleb@...hat.com, mingo@...e.hu,
asharma@...com, vince@...ter.net, wcohen@...hat.com
Subject: Re: [PATCH] perf_events: proposed fix for broken intr throttling
(v2)
On Fri, 2012-01-06 at 19:19 +0100, Stephane Eranian wrote:
> The throttling mechanism REQUIRES that the hwc->interrupts counter be reset
> at EACH timer tick.
Just to be contrary.. :-)
---
include/linux/perf_event.h | 1 +
kernel/events/core.c | 76 +++++++++++++++++++++++++++++++-------------
2 files changed, 55 insertions(+), 22 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 0b91db2..29dedf4 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -589,6 +589,7 @@ struct hw_perf_event {
u64 sample_period;
u64 last_period;
local64_t period_left;
+ u64 interrupts_seq;
u64 interrupts;
u64 freq_time_stamp;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 91fb68a..693e1ce 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2325,11 +2325,14 @@ static void perf_adjust_period(struct perf_event *event, u64 nsec, u64 count)
}
}
+static DEFINE_PER_CPU(int, perf_throttled_count);
+static DEFINE_PER_CPU(u64, perf_throttled_seq);
+
static void perf_ctx_adjust_freq(struct perf_event_context *ctx, u64 period)
{
struct perf_event *event;
struct hw_perf_event *hwc;
- u64 interrupts, now;
+ u64 now;
s64 delta;
if (!ctx->nr_freq)
@@ -2342,22 +2345,11 @@ static void perf_ctx_adjust_freq(struct perf_event_context *ctx, u64 period)
if (!event_filter_match(event))
continue;
- hwc = &event->hw;
-
- interrupts = hwc->interrupts;
- hwc->interrupts = 0;
-
- /*
- * unthrottle events on the tick
- */
- if (interrupts == MAX_INTERRUPTS) {
- perf_log_throttle(event, 1);
- event->pmu->start(event, 0);
- }
-
if (!event->attr.freq || !event->attr.sample_freq)
continue;
+ hwc = &event->hw;
+
event->pmu->read(event);
now = local64_read(&event->count);
delta = now - hwc->freq_count_stamp;
@@ -2441,14 +2433,45 @@ static void perf_rotate_context(struct perf_cpu_context *cpuctx)
list_del_init(&cpuctx->rotation_list);
}
+static void perf_unthrottle_context(struct perf_event_context *ctx)
+{
+ raw_spin_lock(&ctx->lock);
+ list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
+ if (event->state != PERF_EVENT_STATE_ACTIVE)
+ continue;
+
+ if (!event_filter_match(event))
+ continue;
+
+ if (event->hw.interrupts == MAX_INTERRUPTS) {
+ perf_log_throttle(event, 1);
+ event->pmu->start(event, 0);
+ }
+ }
+ raw_spin_unlock(&ctx->lock);
+}
+
void perf_event_task_tick(void)
{
struct list_head *head = &__get_cpu_var(rotation_list);
struct perf_cpu_context *cpuctx, *tmp;
+ int throttle;
WARN_ON(!irqs_disabled());
+ __this_cpu_inc(perf_throttled_seq);
+ throttled = __this_cpu_xchg(perf_throttled_count, 0);
+
list_for_each_entry_safe(cpuctx, tmp, head, rotation_list) {
+ if (throttled) {
+ struct perf_event_context *ctx;
+
+ perf_unthrottle_context(&cpuctx->ctx);
+ ctx = cpuctx->task_ctx;
+ if (ctx)
+ perf_unthrottle_context(ctx);
+ }
+
if (cpuctx->jiffies_interval == 1 ||
!(jiffies % cpuctx->jiffies_interval))
perf_rotate_context(cpuctx);
@@ -4514,6 +4537,7 @@ static int __perf_event_overflow(struct perf_event *event,
{
int events = atomic_read(&event->event_limit);
struct hw_perf_event *hwc = &event->hw;
+ u64 seq;
int ret = 0;
/*
@@ -4523,14 +4547,22 @@ static int __perf_event_overflow(struct perf_event *event,
if (unlikely(!is_sampling_event(event)))
return 0;
- if (unlikely(hwc->interrupts >= max_samples_per_tick)) {
- if (throttle) {
- hwc->interrupts = MAX_INTERRUPTS;
- perf_log_throttle(event, 0);
- ret = 1;
- }
- } else
- hwc->interrupts++;
+ seq = ACCESS_ONCE(__this_cpu_read(perf_throttled_seq));
+
+ if (seq != hwc->interrupts_seq) {
+ hwc->interrupts_seq = seq;
+ hwc->interrupts = 1;
+ } else {
+ if (unlikely(hwc->interrupts >= max_samples_per_tick)) {
+ if (throttle) {
+ __this_cpu_inc(perf_throttled_count);
+ hwc->interrupts = MAX_INTERRUPTS;
+ perf_log_throttle(event, 0);
+ ret = 1;
+ }
+ } else
+ hwc->interrupts++;
+ }
if (event->attr.freq) {
u64 now = perf_clock();
--
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