From: Peter Zijlstra <peterz@infradead.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: mingo@redhat.com, juri.lelli@redhat.com,
dietmar.eggemann@arm.com, rostedt@goodmis.org,
bsegall@google.com, mgorman@suse.de, bristot@redhat.com,
linux-kernel@vger.kernel.org, tim.c.chen@linux.intel.com,
joel@joelfernandes.org
Subject: Re: [PATCH 1/2] sched/fair: skip newidle update stats
Date: Fri, 12 Nov 2021 16:29:41 +0100 [thread overview]
Message-ID: <YY6IZZWuuNN12187@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAKfTPtCGnQc+knLbm=zR-a5T2yEJOZo3CWTJcwHgGdZQ0uYyog@mail.gmail.com>
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?
next prev parent reply other threads:[~2021-11-12 15:30 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-12 9:58 [PATCH 0/2] avoid spurious blocked load update Vincent Guittot
2021-11-12 9:58 ` [PATCH 1/2] sched/fair: skip newidle update stats Vincent Guittot
2021-11-12 14:29 ` Peter Zijlstra
2021-11-12 14:47 ` Vincent Guittot
2021-11-12 15:29 ` Peter Zijlstra [this message]
2021-11-12 16:00 ` Vincent Guittot
2021-11-12 14:55 ` Peter Zijlstra
2021-11-12 14:55 ` Peter Zijlstra
2021-11-12 16:05 ` Vincent Guittot
2021-11-16 23:48 ` [PATCH 0/2] avoid spurious blocked load update Tim Chen
2021-11-18 14:40 ` Vincent Guittot
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