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SubjectRe: [tip:perf/core] perf/core: Check return value of the perf_event_read() IPI
On Tue, Aug 30, 2016 at 09:26:03AM +0200, Peter Zijlstra wrote:
> On Tue, Aug 30, 2016 at 08:47:24AM +0200, Peter Zijlstra wrote:
>
> > If oncpu is not valid, the sched_out that made it invalid will have
> > updated the event count and we're good.
> >
> > All I'll leave is an explicit comment that we've ignored the
> > smp_call_function_single() return value on purpose.
>
> Something like so..

yep, it works in my tests

also I thought there's no group time update in __perf_event_read,
so I was hunting that but then I noticed we do that after during
the read.. and meanwhile came to patch below ;-)

jirka


---
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 305dbd28ea86..c637496251fe 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3440,6 +3440,26 @@ static int find_cpu_to_read(struct perf_event *event, int local_cpu)
return event_cpu;
}

+static void read_update_times(struct perf_event *event, bool group)
+{
+ struct perf_event_context *ctx = event->ctx;
+
+ /*
+ * may read while context is not active
+ * (e.g., thread is blocked), in that case
+ * we cannot update context time
+ */
+ if (ctx->is_active) {
+ update_context_time(ctx);
+ update_cgrp_time_from_event(event);
+ }
+
+ if (group)
+ update_group_times(event);
+ else
+ update_event_times(event);
+}
+
/*
* Cross CPU call to read the hardware event
*/
@@ -3462,12 +3482,9 @@ static void __perf_event_read(void *info)
return;

raw_spin_lock(&ctx->lock);
- if (ctx->is_active) {
- update_context_time(ctx);
- update_cgrp_time_from_event(event);
- }

- update_event_times(event);
+ read_update_times(event, data->group);
+
if (event->state != PERF_EVENT_STATE_ACTIVE)
goto unlock;

@@ -3482,7 +3499,6 @@ static void __perf_event_read(void *info)
pmu->read(event);

list_for_each_entry(sub, &event->sibling_list, group_entry) {
- update_event_times(sub);
if (sub->state == PERF_EVENT_STATE_ACTIVE) {
/*
* Use sibling's PMU rather than @event's since
@@ -3596,19 +3612,7 @@ static int perf_event_read(struct perf_event *event, bool group)
unsigned long flags;

raw_spin_lock_irqsave(&ctx->lock, flags);
- /*
- * may read while context is not active
- * (e.g., thread is blocked), in that case
- * we cannot update context time
- */
- if (ctx->is_active) {
- update_context_time(ctx);
- update_cgrp_time_from_event(event);
- }
- if (group)
- update_group_times(event);
- else
- update_event_times(event);
+ read_update_times(event, group);
raw_spin_unlock_irqrestore(&ctx->lock, flags);
}

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