From: Vincent Guittot <vincent.guittot@linaro.org>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
bristot@redhat.com, linux-kernel@vger.kernel.org,
tim.c.chen@linux.intel.com
Subject: Re: [PATCH v3 4/5] sched/fair: Remove sysctl_sched_migration_cost condition
Date: Fri, 29 Oct 2021 14:30:36 +0200 [thread overview]
Message-ID: <CAKfTPtDEqYa23UmAZS5S9OX07jQr-4DWStoX0uLd2fHScMgNYg@mail.gmail.com> (raw)
In-Reply-To: <2fb13962-0432-2e36-26e6-d05534464294@arm.com>
On Fri, 29 Oct 2021 at 12:02, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>
> On 19/10/2021 14:35, Vincent Guittot wrote:
> > With a default value of 500us, sysctl_sched_migration_cost is
> > significanlty higher than the cost of load_balance. Remove the
>
> Shouldn't this be rather `load balance cost on the lowest sd`? I assume
> here that lb cost stands for sd->max_newidle_lb_cost of the 1st sd.
Both.
During the tests, I did on thx2, the sum of sd->max_newidle_lb_cost
could range between 18us and 829us.
During those tests, I had a limited number of cgroup and the
update_blocked_average could certainly go above the 273us of SMT
sd->max_newidle_lb_cost and the 500us of sysctl_sched_migration_cost
>
> We still use sysctl_sched_migration_cost as a floor against max_cost
> (i.e. lb cost of all sd's) when setting rq->max_idle_balance_cost in
> rebalance_domains().
rq->max_idle_balance_cost is used to cap the value used to compute rq->avg_idle.
>
> And in the add-on discussion (disabling the call to
> nohz_newidle_balance() you mention that sd->max_newidle_lb_cost can be
> higher than sysctl_sched_migration_cost (even when default 500us).
yes, I have reached 273us on thx2 with 2 empty cgroups
>
>
> > condition and rely on the sd->max_newidle_lb_cost to abort
> > newidle_balance.
> >
> > Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> > ---
> > kernel/sched/fair.c | 3 +--
> > 1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index e50fd751e1df..57eae0ebc492 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -10895,8 +10895,7 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
> > rcu_read_lock();
> > sd = rcu_dereference_check_sched_domain(this_rq->sd);
> >
> > - if (this_rq->avg_idle < sysctl_sched_migration_cost ||
> > - !READ_ONCE(this_rq->rd->overload) ||
> > + if (!READ_ONCE(this_rq->rd->overload) ||
> > (sd && this_rq->avg_idle < sd->max_newidle_lb_cost)) {
> >
> > if (sd)
> >
>
next prev parent reply other threads:[~2021-10-29 12:30 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-19 12:35 [PATCH v3 0/5] Improve newidle lb cost tracking and early abort Vincent Guittot
2021-10-19 12:35 ` [PATCH v3 1/5] sched/fair: Account update_blocked_averages in newidle_balance cost Vincent Guittot
2021-10-21 9:43 ` Mel Gorman
2021-10-31 10:16 ` [tip: sched/core] " tip-bot2 for Vincent Guittot
2021-10-19 12:35 ` [PATCH v3 2/5] sched/fair: Skip update_blocked_averages if we are defering load balance Vincent Guittot
2021-10-21 9:44 ` Mel Gorman
2021-10-21 12:45 ` Vincent Guittot
2021-10-31 10:16 ` [tip: sched/core] " tip-bot2 for Vincent Guittot
2021-10-19 12:35 ` [PATCH 3/5] sched/fair: Wait before decaying max_newidle_lb_cost Vincent Guittot
2021-10-21 9:45 ` Mel Gorman
2021-10-29 10:01 ` Dietmar Eggemann
2021-10-29 12:19 ` Vincent Guittot
2021-10-31 10:16 ` [tip: sched/core] " tip-bot2 for Vincent Guittot
2021-10-19 12:35 ` [PATCH v3 4/5] sched/fair: Remove sysctl_sched_migration_cost condition Vincent Guittot
2021-10-21 9:46 ` Mel Gorman
2021-10-29 10:01 ` Dietmar Eggemann
2021-10-29 12:30 ` Vincent Guittot [this message]
2021-10-31 10:16 ` [tip: sched/core] " tip-bot2 for Vincent Guittot
2021-10-19 12:35 ` [PATCH v3 5/5] sched/fair: cleanup newidle_balance Vincent Guittot
2021-10-21 9:46 ` Mel Gorman
2021-10-31 10:16 ` [tip: sched/core] sched/fair: Cleanup newidle_balance tip-bot2 for Vincent Guittot
2021-10-21 9:52 ` [PATCH v3 0/5] Improve newidle lb cost tracking and early abort Mel Gorman
2021-10-21 12:42 ` Vincent Guittot
2021-10-26 17:25 ` Tim Chen
2021-10-27 8:49 ` Vincent Guittot
2021-10-27 20:53 ` Tim Chen
2021-10-28 12:15 ` Vincent Guittot
2021-10-28 21:36 ` Tim Chen
2021-10-29 17:00 ` Tim Chen
2021-10-31 10:18 ` Vincent Guittot
2021-10-28 23:25 ` Joel Fernandes
2021-10-29 7:49 ` Vincent Guittot
2021-10-29 19:37 ` Joel Fernandes
2021-10-29 10:01 ` Dietmar Eggemann
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