linux-kernel - Re: [PATCH v3 0/2] sched/fair: find_energy_efficient

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Date:   Tue, 4 May 2021 19:49:29 +0800
From:   Xuewen Yan <xuewen.yan94@...il.com>
To:     Pierre Gondois <pierre.gondois@....com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Xuewen Yan <xuewen.yan@...soc.com>, qperret@...rret.net,
        Lukasz.Luba@....com, Dietmar Eggemann <dietmar.eggemann@....com>,
        Vincent.Donnefort@....com, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Benjamin Segall <bsegall@...gle.com>,
        Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH v3 0/2] sched/fair: find_energy_efficient_cpu() enhancements

Hi Pierre，

The two patches look good to me.

Thanks
Xuewen Yan

On Tue, May 4, 2021 at 5:11 PM Pierre Gondois <pierre.gondois@....com> wrote:
>
> Hi Xuewen,
>
> Please let me know if you have some comments,
> Pierre
>
> On 5/4/21 10:07 AM, Pierre Gondois wrote:
> > V2:
> >   - Split the patch in 2. [Quentin]
> >   - Add testing results to the cover-letter. [Dietmar]
> >   - Put back 'rcu_read_unlock()' to unlock the rcu
> >     earlier. [Dietmar]
> >   - Various comments. [Dietmar/Quentin]
> >
> > V3:
> >   - Layout/phrasing. [Dietmar]
> >
> > This patchset prevents underflows in find_energy_efficient_cpu().
> > This is done in the second patch:
> > sched/fair: Fix negative energy delta in find_energy_efficient_cpu()
> >
> > The first patch:
> > sched/fair: Only compute base_energy_pd if necessary
> > prevents an unnecessary call to compute_energy() if no CPU is available
> > in a performance domain (pd).
> > When looping over the pds, it also allows to gather the calls
> > to compute_energy(), reducing the chances of having utilization signals
> > being concurrently updated and having a 'negative delta'.
> >
> > The energy tests of the initial EAS enablement at:
> > https://lkml.kernel.org/r/20181203095628.11858-1-quentin.perret@arm.com
> > have been executed using LISA on a Juno-r2 (2xA57 + 4xA53).
> >
> > To recall the test:
> > "10 iterations of between 10 and 50 periodic rt-app tasks (16ms period,
> > 5% duty-cycle) for 30 seconds with energy measurement. Unit is Joules.
> > The goal is to save energy, so lower is better."
> > "Energy is measured with the onboard energy meter. Numbers include
> > consumption of big and little CPUs."
> >
> > +----------+-----------------+-------------------------+
> > |          | Without patches | With patches            |
> > +----------+--------+--------+------------------+------+
> > | Tasks nb |  Mean  |    CI* | Mean             |  CI* |
> > +----------+--------+--------+------------------+------+
> > |       10 |   6.57 |   0.24 |   6.46 (-1.63%)  | 0.27 |
> > |       20 |  12.44 |   0.21 |  12.44 (-0.01%)  | 0.14 |
> > |       30 |  19.10 |   0.78 |  18.75 (-1.85%)  | 0.15 |
> > |       40 |  27.27 |   0.53 |  27.35 (+0.31%)  | 0.33 |
> > |       50 |  36.55 |   0.42 |  36.28 (-0.74%)  | 0.42 |
> > +----------+-----------------+-------------------------+
> > CI: confidence interval
> >
> > For each line, the intervals of values w/ w/o the patches are
> > overlapping (consider Mean +/- CI). Thus, the energy results shouldn't
> > have been impacted.
> >
> > Pierre Gondois (2):
> >    sched/fair: Only compute base_energy_pd if necessary
> >    sched/fair: Fix negative energy delta in find_energy_efficient_cpu()
> >
> >   kernel/sched/fair.c | 68 ++++++++++++++++++++++++++-------------------
> >   1 file changed, 39 insertions(+), 29 deletions(-)
> >