[PATCH] tick: Don't clear idle and iowait sums on CPU down

[Peter De Schrijver <pdeschrijver@nvidia.com>]

From: Sai Gurrappadi <sgurrappadi@nvidia.com>

NOHZ related per-cpu data is cleared on CPU down. This was introduced by
4b0c0f294 "tick: Cleanup NOHZ per cpu data on cpu down" which breaks
/proc/stats because the idle and iowait sums are now non-monotonic
across a CPU down/up cycle.

Fix this by not clearing the idle_sleeptime and iowait_sleeptime fields
on CPU down.

Signed-off-by: Sai Gurrappadi <sgurrappadi@nvidia.com>
Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
---
 kernel/time/tick-sched.c |   13 ++++++++++++-
 1 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index c12c006..2cd27ec 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -1164,6 +1164,17 @@ void tick_setup_sched_timer(void)
 #endif /* HIGH_RES_TIMERS */
 
 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
+
+static inline void clear_tick_sched(struct tick_sched *ts)
+{
+	ktime_t idle_sleeptime = ts->idle_sleeptime;
+	ktime_t iowait_sleeptime = ts->iowait_sleeptime;
+
+	memset(ts, 0, sizeof(*ts));
+	ts->idle_sleeptime = idle_sleeptime;
+	ts->iowait_sleeptime = iowait_sleeptime;
+}
+
 void tick_cancel_sched_timer(int cpu)
 {
 	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
@@ -1173,7 +1184,7 @@ void tick_cancel_sched_timer(int cpu)
 		hrtimer_cancel(&ts->sched_timer);
 # endif
 
-	memset(ts, 0, sizeof(*ts));
+	clear_tick_sched(ts);
 }
 #endif
 
-- 
1.7.7.rc0.72.g4b5ea.dirty