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 <[email protected]> > --- > 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.
