From: Morten Rasmussen <morten.rasmussen@arm.com>
To: Sai Gurrappadi <sgurrappadi@nvidia.com>
Cc: peterz@infradead.org, mingo@redhat.com, dietmar.eggemann@arm.com,
yuyang.du@intel.com, vincent.guittot@linaro.org,
mgalbraith@suse.de, linux-kernel@vger.kernel.org,
Peter Boonstoppel <pboonstoppel@nvidia.com>
Subject: Re: [PATCH v2 11/13] sched/fair: Avoid pulling tasks from non-overloaded higher capacity groups
Date: Fri, 15 Jul 2016 09:39:49 +0100 [thread overview]
Message-ID: <20160715083949.GF21816@e105550-lin.cambridge.arm.com> (raw)
In-Reply-To: <5787C03B.8010906@nvidia.com>
On Thu, Jul 14, 2016 at 09:39:23AM -0700, Sai Gurrappadi wrote:
> On 06/30/2016 12:49 AM, Morten Rasmussen wrote:
> > On Thu, Jun 23, 2016 at 02:20:48PM -0700, Sai Gurrappadi wrote:
> >> Hi Morten,
> >>
> >> On 06/22/2016 10:03 AM, Morten Rasmussen wrote:
> >>
> >> [...]
> >>
> >>>
> >>> +/*
> >>> + * group_smaller_cpu_capacity: Returns true if sched_group sg has smaller
> >>> + * per-cpu capacity than sched_group ref.
> >>> + */
> >>> +static inline bool
> >>> +group_smaller_cpu_capacity(struct sched_group *sg, struct sched_group *ref)
> >>> +{
> >>> + return sg->sgc->max_capacity * capacity_margin <
> >>> + ref->sgc->max_capacity * 1024;
> >>> +}
> >>> +
> >>> static inline enum
> >>> group_type group_classify(struct sched_group *group,
> >>> struct sg_lb_stats *sgs)
> >>> @@ -6892,6 +6903,19 @@ static bool update_sd_pick_busiest(struct lb_env *env,
> >>> if (sgs->avg_load <= busiest->avg_load)
> >>> return false;
> >>>
> >>> + if (!(env->sd->flags & SD_ASYM_CPUCAPACITY))
> >>> + goto asym_packing;
> >>> +
> >>> + /* Candidate sg has no more than one task per cpu and has
> >>> + * higher per-cpu capacity. Migrating tasks to less capable
> >>> + * cpus may harm throughput. Maximize throughput,
> >>> + * power/energy consequences are not considered.
> >>> + */
> >>> + if (sgs->sum_nr_running <= sgs->group_weight &&
> >>> + group_smaller_cpu_capacity(sds->local, sg))
> >>> + return false;
> >>> +
> >>> +asym_packing:
> >>
> >> What about the case where IRQ/RT work reduces the capacity of some of
> >> these bigger CPUs? sgc->max_capacity might not necessarily capture
> >> that case.
> >
> > Right, we could possibly improve this by using min_capacity instead, but
> > we could end up allowing tasks to be pulled to lower capacity cpus just
> > because one big cpu has reduced capacity due to RT/IRQ pressure and
> > therefore has lowered the groups min_capacity.
> >
> > Ideally we should check all the capacities, but that complicates things
> > a lot.
> >
> > Would you prefer min_capacity instead, or attempts to consider all the
> > cpu capacities available in both groups?
> >
>
> min_capacity as a start works I think given that we are only trying to
> make existing LB better, not necessarily optimizing for every case.
> Might have to revisit this anyways for thermals etc.
Agreed, I will make it min_capacity instead of max_capacity in v3.
Thanks,
Morten
next prev parent reply other threads:[~2016-07-15 8:38 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-22 17:03 [PATCH v2 00/13] sched: Clean-ups and asymmetric cpu capacity support Morten Rasmussen
2016-06-22 17:03 ` [PATCH v2 01/13] sched: Fix power to capacity renaming in comment Morten Rasmussen
2016-08-10 18:03 ` [tip:sched/core] sched/core: " tip-bot for Morten Rasmussen
2016-06-22 17:03 ` [PATCH v2 02/13] sched/fair: Consistent use of prev_cpu in wakeup path Morten Rasmussen
2016-06-22 18:04 ` Rik van Riel
2016-06-23 9:56 ` Morten Rasmussen
2016-06-23 12:24 ` Rik van Riel
2016-08-10 18:03 ` [tip:sched/core] sched/fair: Make the use of prev_cpu consistent in the " tip-bot for Morten Rasmussen
2016-06-22 17:03 ` [PATCH v2 03/13] sched/fair: Optimize find_idlest_cpu() when there is no choice Morten Rasmussen
2016-07-13 12:20 ` Vincent Guittot
2016-08-10 18:03 ` [tip:sched/core] " tip-bot for Morten Rasmussen
2016-06-22 17:03 ` [PATCH v2 04/13] sched: Introduce SD_ASYM_CPUCAPACITY sched_domain topology flag Morten Rasmussen
2016-07-11 9:55 ` Peter Zijlstra
2016-07-11 10:42 ` Morten Rasmussen
2016-06-22 17:03 ` [PATCH v2 05/13] sched: Enable SD_BALANCE_WAKE for asymmetric capacity systems Morten Rasmussen
2016-07-11 10:04 ` Peter Zijlstra
2016-07-11 10:37 ` Morten Rasmussen
2016-07-11 11:04 ` Morten Rasmussen
2016-07-11 11:24 ` Peter Zijlstra
2016-07-12 14:26 ` Morten Rasmussen
2016-06-22 17:03 ` [PATCH v2 06/13] sched: Store maximum per-cpu capacity in root domain Morten Rasmussen
2016-07-11 10:18 ` Peter Zijlstra
2016-07-11 16:16 ` Dietmar Eggemann
2016-07-12 11:42 ` Peter Zijlstra
2016-07-13 11:18 ` Dietmar Eggemann
2016-07-13 12:40 ` Vincent Guittot
2016-07-13 13:48 ` Dietmar Eggemann
2016-07-13 16:37 ` Morten Rasmussen
2016-07-14 13:25 ` Vincent Guittot
2016-07-14 15:15 ` Morten Rasmussen
2016-07-15 11:46 ` Morten Rasmussen
2016-07-15 13:39 ` Vincent Guittot
2016-07-15 16:02 ` Morten Rasmussen
2016-07-18 12:48 ` Vincent Guittot
2016-07-18 15:11 ` Morten Rasmussen
2016-06-22 17:03 ` [PATCH v2 07/13] sched/fair: Let asymmetric cpu configurations balance at wake-up Morten Rasmussen
2016-07-11 11:13 ` Peter Zijlstra
2016-07-11 12:32 ` Morten Rasmussen
2016-07-13 12:56 ` Vincent Guittot
2016-07-13 16:14 ` Morten Rasmussen
2016-07-14 13:45 ` Vincent Guittot
2016-07-15 8:37 ` Morten Rasmussen
2016-06-22 17:03 ` [PATCH v2 08/13] sched/fair: Compute task/cpu utilization at wake-up more correctly Morten Rasmussen
2016-06-22 17:03 ` [PATCH v2 09/13] sched/fair: Consider spare capacity in find_idlest_group() Morten Rasmussen
2016-06-22 17:03 ` [PATCH v2 10/13] sched: Add per-cpu max capacity to sched_group_capacity Morten Rasmussen
2016-06-22 17:03 ` [PATCH v2 11/13] sched/fair: Avoid pulling tasks from non-overloaded higher capacity groups Morten Rasmussen
2016-06-23 21:20 ` Sai Gurrappadi
2016-06-30 7:49 ` Morten Rasmussen
2016-07-14 16:39 ` Sai Gurrappadi
2016-07-15 8:39 ` Morten Rasmussen [this message]
2016-07-12 12:59 ` Peter Zijlstra
2016-07-12 14:34 ` Morten Rasmussen
2016-06-22 17:03 ` [PATCH v2 12/13] arm: Set SD_ASYM_CPUCAPACITY for big.LITTLE platforms Morten Rasmussen
2016-06-22 17:03 ` [PATCH v2 13/13] arm: Update arch_scale_cpu_capacity() to reflect change to define Morten Rasmussen
2016-06-28 10:20 ` [PATCH v2 00/13] sched: Clean-ups and asymmetric cpu capacity support Koan-Sin Tan
2016-06-30 7:53 ` Morten Rasmussen
2016-07-08 7:35 ` KEITA KOBAYASHI
2016-07-08 8:18 ` Morten Rasmussen
2016-07-11 8:33 ` Morten Rasmussen
2016-07-11 12:44 ` Vincent Guittot
2016-07-12 13:25 ` Peter Zijlstra
2016-07-12 14:39 ` Morten Rasmussen
2016-07-13 12:06 ` Vincent Guittot
2016-07-13 15:54 ` Morten Rasmussen
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