perf: Add perf_event::child_count

Only child counters adding back their values into the parent counter
are responsible for cross-cpu updates to event->count.

So if we pull that out into a new child_count variable, we get an
event->count that is only modified locally.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 3 insertions, 2 deletions

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 441992a9775c..f34dab9b275e 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -671,6 +671,7 @@ struct perf_event {
         enum perf_event_active_state    state;
         unsigned int                    attach_state;
         atomic64_t                      count;
+        atomic64_t                      child_count;
 
         /*
          * These are the total time in nanoseconds that the event
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index ab4c0ffc271c..a395fda2d94c 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -1738,7 +1738,7 @@ static void __perf_event_read(void *info)
 
 static inline u64 perf_event_count(struct perf_event *event)
 {
-        return atomic64_read(&event->count);
+        return atomic64_read(&event->count) + atomic64_read(&event->child_count);
 }
 
 static u64 perf_event_read(struct perf_event *event)
@@ -5379,7 +5379,7 @@ static void sync_child_event(struct perf_event *child_event,
         /*
          * Add back the child's count to the parent's count:
          */
-        atomic64_add(child_val, &parent_event->count);
+        atomic64_add(child_val, &parent_event->child_count);
         atomic64_add(child_event->total_time_enabled,
                      &parent_event->child_total_time_enabled);
         atomic64_add(child_event->total_time_running,