From: Morten Rasmussen <morten.rasmussen@arm.com>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: "peterz@infradead.org" <peterz@infradead.org>,
"mingo@kernel.org" <mingo@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"preeti@linux.vnet.ibm.com" <preeti@linux.vnet.ibm.com>,
"kamalesh@linux.vnet.ibm.com" <kamalesh@linux.vnet.ibm.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"riel@redhat.com" <riel@redhat.com>,
"efault@gmx.de" <efault@gmx.de>,
"nicolas.pitre@linaro.org" <nicolas.pitre@linaro.org>,
"linaro-kernel@lists.linaro.org" <linaro-kernel@lists.linaro.org>
Subject: Re: [PATCH v9 10/10] sched: move cfs task on a CPU with higher capacity
Date: Mon, 24 Nov 2014 17:30:46 +0000 [thread overview]
Message-ID: <20141124173046.GM23177@e105550-lin.cambridge.arm.com> (raw)
In-Reply-To: <CAKfTPtC9tew3wzoWfyxOWJR8MtpL+jjwWoA9Lkpk4opVUEXcxQ@mail.gmail.com>
On Mon, Nov 24, 2014 at 02:45:45PM +0000, Vincent Guittot wrote:
> On 21 November 2014 at 13:37, Morten Rasmussen <morten.rasmussen@arm.com> wrote:
> > On Mon, Nov 03, 2014 at 04:54:47PM +0000, Vincent Guittot wrote:
>
> >>
> >> + /*
> >> + * The dst_cpu is idle and the src_cpu CPU has only 1 CFS task.
> >> + * It's worth migrating the task if the src_cpu's capacity is reduced
> >> + * because of other sched_class or IRQs whereas capacity stays
> >> + * available on dst_cpu.
> >> + */
> >> + if ((env->idle != CPU_NOT_IDLE) &&
> >> + (env->src_rq->cfs.h_nr_running == 1)) {
> >> + unsigned long src_eff_capacity, dst_eff_capacity;
> >> +
> >> + dst_eff_capacity = 100;
> >> + dst_eff_capacity *= capacity_of(env->dst_cpu);
> >> + dst_eff_capacity *= capacity_orig_of(env->src_cpu);
> >> +
> >> + src_eff_capacity = sd->imbalance_pct;
> >> + src_eff_capacity *= capacity_of(env->src_cpu);
> >> + src_eff_capacity *= capacity_orig_of(env->dst_cpu);
> >
> > Do we need to scale by capacity_orig? Shouldn't the absolute capacity be
> > better?
> >
> > if (capacity_of(env->src) * sd->imbalance_pct < capacity_of(env->dst) *
> > 100) ?
>
> we don't want to compare absolute capacity between CPUs but to compare
> the reduction of their capacity because we want to choose the CPU
> which is less used by RT tasks or irq
But least relative RT load doesn't necessarily mean most available
compute capacity. 50% RT use of a capacity_orig = 1000 (capacity_of(cpu) =
500, eff_capacity = 50%) gives better CFS throughput than 20% RT use of
a capacity_orig = 500 (capacity_of(cpu) = 400, eff_capacity = 80%). Why pick
the cpu with less throughput?
Morten
>
> Regards,
> Vincent
> >
> > Isn't it the absolute available capacity that matters? For SMP
> > capacity_orig is the same and cancels out and doesn't change anything.
> > For big.LITTLE we would rather have the task run on a big where rt/irq
> > eats 30% than a little cpu where rq/irq eats 5%, assuming big capacity
> > is much bigger than little capacity so the absolute available capacity
> > (~cycles/time) is larger on the big cpu.
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at http://www.tux.org/lkml/
>
next prev parent reply other threads:[~2014-11-24 17:29 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-03 16:54 [PATCH v9 00/10] sched: consolidation of CPU capacity and usage Vincent Guittot
2014-11-03 16:54 ` [PATCH v9 01/10] sched: add utilization_avg_contrib Vincent Guittot
2014-11-21 12:34 ` Morten Rasmussen
2014-11-24 14:04 ` Vincent Guittot
2014-11-24 17:34 ` Morten Rasmussen
2014-11-03 16:54 ` [PATCH v9 02/10] sched: Track group sched_entity usage contributions Vincent Guittot
2014-11-21 12:35 ` Morten Rasmussen
2014-11-24 14:04 ` Vincent Guittot
2014-11-24 15:39 ` Morten Rasmussen
2014-11-03 16:54 ` [PATCH v9 03/10] sched: remove frequency scaling from cpu_capacity Vincent Guittot
2014-11-21 12:35 ` Morten Rasmussen
2014-11-03 16:54 ` [PATCH v9 04/10] sched: Make sched entity usage tracking scale-invariant Vincent Guittot
2014-11-21 12:35 ` Morten Rasmussen
2014-11-26 16:05 ` Dietmar Eggemann
2014-11-03 16:54 ` [PATCH v9 05/10] sched: make scale_rt invariant with frequency Vincent Guittot
2014-11-21 12:35 ` Morten Rasmussen
2014-11-24 14:24 ` Vincent Guittot
2014-11-24 17:05 ` Morten Rasmussen
2014-11-25 13:48 ` Vincent Guittot
2014-11-26 11:57 ` Morten Rasmussen
2014-11-25 2:24 ` Wanpeng Li
2014-11-25 13:52 ` Vincent Guittot
2014-11-26 5:18 ` Wanpeng Li
2014-11-26 8:27 ` Vincent Guittot
2014-11-03 16:54 ` [PATCH v9 06/10] sched: add per rq cpu_capacity_orig Vincent Guittot
2014-11-03 16:54 ` [PATCH v9 07/10] sched: get CPU's usage statistic Vincent Guittot
2014-11-21 12:36 ` Morten Rasmussen
2014-11-03 16:54 ` [PATCH v9 08/10] sched: replace capacity_factor by usage Vincent Guittot
2014-11-19 15:15 ` pang.xunlei
2014-11-19 17:30 ` Vincent Guittot
2014-11-21 12:37 ` Morten Rasmussen
2014-11-24 14:41 ` Vincent Guittot
2014-11-24 17:16 ` Morten Rasmussen
2014-11-03 16:54 ` [PATCH v9 09/10] sched: add SD_PREFER_SIBLING for SMT level Vincent Guittot
2014-11-03 16:54 ` [PATCH v9 10/10] sched: move cfs task on a CPU with higher capacity Vincent Guittot
2014-11-21 12:37 ` Morten Rasmussen
2014-11-24 14:45 ` Vincent Guittot
2014-11-24 17:30 ` Morten Rasmussen [this message]
2014-11-21 12:34 ` [PATCH v9 00/10] sched: consolidation of CPU capacity and usage Morten Rasmussen
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