From: Quentin Perret <quentin.perret@arm.com>
To: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>,
linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Thara Gopinath <thara.gopinath@linaro.org>,
linux-pm@vger.kernel.org,
Morten Rasmussen <morten.rasmussen@arm.com>,
Chris Redpath <chris.redpath@arm.com>,
Valentin Schneider <valentin.schneider@arm.com>,
"Rafael J . Wysocki" <rjw@rjwysocki.net>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
Todd Kjos <tkjos@google.com>, Joel Fernandes <joelaf@google.com>
Subject: Re: [RFC PATCH 5/6] sched/fair: Select an energy-efficient CPU on task wake-up
Date: Sun, 25 Mar 2018 02:52:39 +0100 [thread overview]
Message-ID: <20180325015238.GB1803@queper01-VirtualBox> (raw)
In-Reply-To: <20180321153518.GC13951@e110439-lin>
On Wednesday 21 Mar 2018 at 15:35:18 (+0000), Patrick Bellasi wrote:
> On 20-Mar 09:43, Dietmar Eggemann wrote:
> > From: Quentin Perret <quentin.perret@arm.com>
>
> [...]
>
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 76bd46502486..65a1bead0773 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -6513,6 +6513,60 @@ static unsigned long compute_energy(struct task_struct *p, int dst_cpu)
> > return energy;
> > }
> >
> > +static bool task_fits(struct task_struct *p, int cpu)
> > +{
> > + unsigned long next_util = cpu_util_next(cpu, p, cpu);
> > +
> > + return util_fits_capacity(next_util, capacity_orig_of(cpu));
> ^^^^^^^^^^^^^^^^^^^^^
>
> Since here we are at scheduling CFS tasks, should we not better use
> capacity_of() to account for RT/IRQ pressure ?
Yes, definitely. I change this in v2.
>
> > +}
> > +
> > +static int find_energy_efficient_cpu(struct sched_domain *sd,
> > + struct task_struct *p, int prev_cpu)
> > +{
> > + unsigned long cur_energy, prev_energy, best_energy;
> > + int cpu, best_cpu = prev_cpu;
> > +
> > + if (!task_util(p))
>
> We are still waking up a task... what if the task was previously
> running on a big CPU which is now idle?
>
> I understand that from a _relative_ energy_diff standpoint there is
> not much to do for a 0 utilization task. However, for those tasks we
> can still try to return the most energy efficient CPU among the ones
> in their cpus_allowed mask.
>
> It should be a relatively low overhead (maybe contained in a fallback
> most_energy_efficient_cpu() kind of function) which allows, for
> example on ARM big.LITTLE systems, to consolidate those tasks on
> LITTLE CPUs instead for example keep running them on a big CPU.
Hmmmm so the difficult thing about a task with 0 util is that you don't
know if this is really a small task, or a big task with a very long
period. The only useful thing you know for sure about the task is where
it ran last time, so I guess that makes sense to use that information
rather than make assumptions. There is no perfect solution using the
util_avg of the task.
Now, UTIL_EST is changing the game here. If we use it for task placement
(which I think is the right thing to do), this issue should be a lot
easier to solve. What do you think ?
Thanks,
Quentin
next prev parent reply other threads:[~2018-03-25 1:52 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-20 9:43 [RFC PATCH 0/6] Energy Aware Scheduling Dietmar Eggemann
2018-03-20 9:43 ` [RFC PATCH 1/6] sched/fair: Create util_fits_capacity() Dietmar Eggemann
2018-03-20 9:43 ` [RFC PATCH 2/6] sched: Introduce energy models of CPUs Dietmar Eggemann
2018-03-20 9:52 ` Greg Kroah-Hartman
2018-03-21 0:45 ` Quentin Perret
2018-03-25 13:48 ` Quentin Perret
2018-03-26 22:26 ` Dietmar Eggemann
2018-04-09 12:01 ` Peter Zijlstra
2018-04-09 13:45 ` Quentin Perret
2018-04-09 15:32 ` Peter Zijlstra
2018-04-09 16:42 ` Quentin Perret
2018-04-10 6:55 ` Rafael J. Wysocki
2018-04-10 9:31 ` Quentin Perret
2018-04-10 10:20 ` Rafael J. Wysocki
2018-03-20 9:43 ` [RFC PATCH 3/6] sched: Add over-utilization/tipping point indicator Dietmar Eggemann
2018-04-09 9:40 ` Peter Zijlstra
2018-04-09 9:47 ` Peter Zijlstra
2018-04-09 9:53 ` Dietmar Eggemann
2018-04-09 11:49 ` Peter Zijlstra
2018-03-20 9:43 ` [RFC PATCH 4/6] sched/fair: Introduce an energy estimation helper function Dietmar Eggemann
2018-03-21 9:04 ` Juri Lelli
2018-03-21 12:26 ` Patrick Bellasi
2018-03-21 12:59 ` Juri Lelli
2018-03-21 13:55 ` Quentin Perret
2018-03-21 15:15 ` Juri Lelli
2018-03-21 16:26 ` Morten Rasmussen
2018-03-21 17:02 ` Juri Lelli
2018-03-21 14:02 ` Quentin Perret
2018-03-21 21:15 ` Dietmar Eggemann
2018-03-21 12:39 ` Patrick Bellasi
2018-03-21 14:26 ` Quentin Perret
2018-03-21 14:50 ` Juri Lelli
2018-03-21 15:54 ` Patrick Bellasi
2018-03-22 5:05 ` Quentin Perret
2018-03-20 9:43 ` [RFC PATCH 5/6] sched/fair: Select an energy-efficient CPU on task wake-up Dietmar Eggemann
2018-03-21 15:35 ` Patrick Bellasi
2018-03-22 20:10 ` Joel Fernandes
2018-03-23 15:47 ` Morten Rasmussen
2018-03-24 1:13 ` Joel Fernandes
2018-03-24 1:34 ` Quentin Perret
2018-03-24 6:06 ` Joel Fernandes
2018-03-24 1:22 ` Quentin Perret
2018-03-25 1:52 ` Quentin Perret [this message]
2018-03-22 16:27 ` Joel Fernandes
2018-03-22 18:06 ` Patrick Bellasi
2018-03-22 20:19 ` Joel Fernandes
2018-03-24 1:47 ` Quentin Perret
2018-03-25 0:12 ` Joel Fernandes
2018-03-23 16:00 ` Morten Rasmussen
2018-03-24 0:36 ` Joel Fernandes
2018-03-25 1:38 ` Quentin Perret
2018-03-20 9:43 ` [RFC PATCH 6/6] drivers: base: arch_topology.c: Enable EAS for arm/arm64 platforms Dietmar Eggemann
2018-03-20 9:49 ` Greg Kroah-Hartman
2018-03-20 15:20 ` Dietmar Eggemann
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