Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 12 Nov 2021 17:00:04 +0100 | Subject | Re: [PATCH 1/2] sched/fair: skip newidle update stats |
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On Fri, 12 Nov 2021 at 16:29, Peter Zijlstra <peterz@infradead.org> wrote: > > On Fri, Nov 12, 2021 at 03:47:21PM +0100, Vincent Guittot wrote: > > On Fri, 12 Nov 2021 at 15:29, Peter Zijlstra <peterz@infradead.org> wrote: > > > > > > On Fri, Nov 12, 2021 at 10:58:56AM +0100, Vincent Guittot wrote: > > > > In case we skip the newly idle LB entirely or we abort it because we are > > > > going to exceed the avg_idle, we have to make sure to not start an update > > > > of the blocked load when entering idle > > > > > > > > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > > > > --- > > > > kernel/sched/fair.c | 18 ++++++++++++++---- > > > > 1 file changed, 14 insertions(+), 4 deletions(-) > > > > > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > > > index 13950beb01a2..a162b0ec8963 100644 > > > > --- a/kernel/sched/fair.c > > > > +++ b/kernel/sched/fair.c > > > > @@ -10861,7 +10861,7 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf) > > > > int this_cpu = this_rq->cpu; > > > > u64 t0, t1, curr_cost = 0; > > > > struct sched_domain *sd; > > > > - int pulled_task = 0; > > > > + int pulled_task = 0, early_stop = 0; > > > > > > > > update_misfit_status(NULL, this_rq); > > > > > > > > @@ -10898,8 +10898,16 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf) > > > > if (!READ_ONCE(this_rq->rd->overload) || > > > > (sd && this_rq->avg_idle < sd->max_newidle_lb_cost)) { > > > > > > > > - if (sd) > > > > + if (sd) { > > > > update_next_balance(sd, &next_balance); > > > > + > > > > + /* > > > > + * We skip new idle LB because there is not enough > > > > + * time before next wake up. Make sure that we will > > > > + * not kick NOHZ_NEWILB_KICK > > > > + */ > > > > + early_stop = 1; > > > > + } > > > > rcu_read_unlock(); > > > > > > > > goto out; > > > > Anyway, does nohz_newidle_balance() want to loose it's ->avg_idle test > > > with this on? > > > > This test still covers cases with short newly idle balance. Being > > conservative, people never complained that the update of blocked load > > average of idle CPUs doesn't happen often enough. It's most often the > > opposite > > Well, per commit c5b0a7eefc70 ("sched/fair: Remove > sysctl_sched_migration_cost condition") combined with the above change, > we no longer call nohz_newidle_balance() in exactly that condition, > right? > > Or are we worried about that !overload case?
we can do a complete newly idle LB but have this_rq->avg_idle < sysctl_sched_migration_cost. In this case, the condition will continue to skip update of other idle CPUs
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