From: Joel Fernandes <joelaf@google.com>
To: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Patrick Bellasi <patrick.bellasi@arm.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Quentin Perret <quentin.perret@arm.com>,
Thara Gopinath <thara.gopinath@linaro.org>,
Linux PM <linux-pm@vger.kernel.org>,
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>
Subject: Re: [RFC PATCH 5/6] sched/fair: Select an energy-efficient CPU on task wake-up
Date: Fri, 23 Mar 2018 18:13:56 -0700 [thread overview]
Message-ID: <CAJWu+oqP9NLkhhZsTZ5JogSWgp6D2FoGAmP76Szi4+n87XNSsQ@mail.gmail.com> (raw)
In-Reply-To: <20180323154745.GP4589@e105550-lin.cambridge.arm.com>
Hi Morten,
On Fri, Mar 23, 2018 at 8:47 AM, Morten Rasmussen
<morten.rasmussen@arm.com> wrote:
> On Thu, Mar 22, 2018 at 01:10:22PM -0700, Joel Fernandes wrote:
>> On Wed, Mar 21, 2018 at 8:35 AM, Patrick Bellasi
>> <patrick.bellasi@arm.com> wrote:
>> > [...]
>> >
>> >> @@ -6555,6 +6613,14 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
>> >> break;
>> >> }
>> >>
>> >> + /*
>> >> + * Energy-aware task placement is performed on the highest
>> >> + * non-overutilized domain spanning over cpu and prev_cpu.
>> >> + */
>> >> + if (want_energy && !sd_overutilized(tmp) &&
>> >> + cpumask_test_cpu(prev_cpu, sched_domain_span(tmp)))
>> >> + energy_sd = tmp;
>> >> +
>> >
>> > Not entirely sure, but I was trying to understand if we can avoid to
>> > modify the definition of want_affine (in the previous chunk) and move
>> > this block before the previous "if (want_affine..." (in mainline but
>> > not in this chunk), which will became an else, e.g.
>> >
>> > if (want_energy && !sd_overutilized(tmp) &&
>> > // ...
>> > else if (want_energy && !sd_overutilized(tmp) &&
>> > // ...
>> >
>> > Isn't that the same?
>> >
>> > Maybe there is a code path I'm missing... but otherwise it seems a
>> > more self contained modification of select_task_rq_fair...
>>
>> Just replying to this here Patrick instead of the other thread.
>>
>> I think this is the right place for the block from Quentin quoted
>> above because we want to search for the highest domain that is
>> !overutilized and look among those for the candidates. So from that
>> perspective, we can't move the block to the beginning and it seems to
>> be in the right place. My main concern on the other thread was
>> different, I was talking about the cases where sd_flag & tmp->flags
>> don't match. In that case, sd = NULL would trump EAS and I was
>> wondering if that's the right thing to do...
>
> You mean if SD_BALANCE_WAKE isn't set on sched_domains?
Yes.
> The current code seems to rely on that flag to be set to work correctly.
> Otherwise, the loop might bail out on !want_affine and we end up doing
> the find_energy_efficient_cpu() on the lowest level sched_domain even if
> there is higher level one which isn't over-utilized.
>
> However, SD_BALANCE_WAKE should be set if SD_ASYM_CPUCAPACITY is set so
> sd == NULL shouldn't be possible? This only holds as long as we only
> want EAS for asymmetric systems.
Yes, I see you had topology code that set SD_BALANCE_WAKE for ASYM. It
makes sense to me then, thanks for the clarification.
Still I feel it is a bit tedious/confusing when reading code to draw
the conclusion about why sd is checked first before doing
find_energy_efficient_cpu (and that sd will != NULL for ASYM systems).
If energy_sd is set, then we can just proceed with EAS without
checking that sd != NULL. This function in mainline is already pretty
confusing as it is :-(
Regards,
- Joel
next prev parent reply other threads:[~2018-03-24 1:13 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 [this message]
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
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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