The way loadavg is tracked during nohz only pays attention to the load
upon entering nohz. This can be particularly noticeable if nohz is
entered while non-idle, and then the cpu goes idle and stays that way for
a long time. We've had reports of a loadavg near 150 on a mostly idle
system.
Calling calc_load_nohz_start() regardless of whether the tick is already
stopped addresses the issue when going idle. Tracking load changes when
not going idle (e.g. multiple SCHED_FIFO tasks coming and going) is not
addressed by this patch.
Signed-off-by: Scott Wood <sw...@redhat.com>
---
kernel/time/tick-sched.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 955851748dc3..f177d8168400 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -763,6 +763,9 @@ static void tick_nohz_stop_tick(struct tick_sched *ts, int
cpu)
ts->do_timer_last = 0;
}
+ /* Even if the tick was already stopped, load may have changed */
+ calc_load_nohz_start();
+
/* Skip reprogram of event if its not changed */
if (ts->tick_stopped && (expires == ts->next_tick)) {
/* Sanity check: make sure clockevent is actually programmed */
@@ -783,7 +786,6 @@ static void tick_nohz_stop_tick(struct tick_sched *ts, int
cpu)
* the scheduler tick in nohz_restart_sched_tick.
*/
if (!ts->tick_stopped) {
- calc_load_nohz_start();
quiet_vmstat();
ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
--
1.8.3.1
