perf_event: Cleanup for cpu_clock_perf_event_update()

Using atomic64_xchg() instead of atomic64_read() and
atomic64_set().

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <4B1F19DC.90204@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 1 insertions, 2 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 77641ae6b23f..94e1b28333ae 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -4079,8 +4079,7 @@ static void cpu_clock_perf_event_update(struct perf_event *event)
         u64 now;
 
         now = cpu_clock(cpu);
-        prev = atomic64_read(&event->hw.prev_count);
-        atomic64_set(&event->hw.prev_count, now);
+        prev = atomic64_xchg(&event->hw.prev_count, now);
         atomic64_add(now - prev, &event->count);
 }