commit ec89a06fd4e12301f11ab039ee07d2353a18addc
author Xiao Guangrong <xiaoguangrong@cn.fujitsu.com> Wed Dec 09 11:30:36 2009 +0800
committer Ingo Molnar <mingo@elte.hu> Wed Dec 09 09:56:27 2009 +0100
tree 507d33bda6504dd8422b9952156d338b0200fb2b
parent b93f7978ad6b46133e9453b90ccc057dc2429e75

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>

kernel/perf_event.c

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 77641ae..94e1b28 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -4079,8 +4079,7 @@
 	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);
 }