* [PATCH] tick-sched: Update nohz load even if tick already stopped
@ 2019-10-02 22:55 Scott Wood
2019-10-09 15:45 ` Frederic Weisbecker
0 siblings, 1 reply; 2+ messages in thread
From: Scott Wood @ 2019-10-02 22:55 UTC (permalink / raw)
To: Frederic Weisbecker, Thomas Gleixner, Ingo Molnar
Cc: linux-kernel, Scott Wood
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 <swood@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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] tick-sched: Update nohz load even if tick already stopped
2019-10-02 22:55 [PATCH] tick-sched: Update nohz load even if tick already stopped Scott Wood
@ 2019-10-09 15:45 ` Frederic Weisbecker
0 siblings, 0 replies; 2+ messages in thread
From: Frederic Weisbecker @ 2019-10-09 15:45 UTC (permalink / raw)
To: Scott Wood
Cc: Frederic Weisbecker, Thomas Gleixner, Ingo Molnar, linux-kernel
On Wed, Oct 02, 2019 at 06:55:35PM -0400, Scott Wood wrote:
> 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 <swood@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);
Thanks. I've pondered over your patch to try to avoid calling
calc_load_nohz_start() unconditionally like that. But in the end the
fast path of this function shouldn't bring much overhead and does pretty
much the same as what I would do to call it conditionally.
So I'm applying it.
^ permalink raw reply [flat|nested] 2+ messages in thread
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