From: Lukasz Luba <lukasz.luba@arm.com>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: peterz@infradead.org, vincent.guittot@linaro.org,
linux-kernel@vger.kernel.org, Chris.Redpath@arm.com,
morten.rasmussen@arm.com, qperret@google.com,
linux-pm@vger.kernel.org, stable@vger.kernel.org,
rjw@rjwysocki.net, viresh.kumar@linaro.org, mingo@redhat.com,
juri.lelli@redhat.com, rostedt@goodmis.org, segall@google.com,
mgorman@suse.de, bristot@redhat.com, CCj.Yeh@mediatek.com
Subject: Re: [PATCH v2 1/1] PM: EM: Increase energy calculation precision
Date: Tue, 3 Aug 2021 11:08:26 +0100 [thread overview]
Message-ID: <82d9d384-80e0-f5ec-cb09-6804a713a690@arm.com> (raw)
In-Reply-To: <461df215-8f78-2f29-aaba-636aebb21337@arm.com>
On 8/3/21 10:44 AM, Dietmar Eggemann wrote:
> On 02/08/2021 08:21, Lukasz Luba wrote:
>> Hi Peter, Vincent,
>>
>> Gentle ping.
>>
>>
>> On 7/20/21 10:41 AM, Lukasz Luba wrote:
>
> [...]
>
>>> There are corner cases when the EAS energy calculation for two
>>> Performance
>>> Domains (PDs) return the same value. The EAS compares these values to
>>> choose smaller one. It might happen that this values are equal due to
>>> rounding error. In such scenario, we need better resolution, e.g. 1000
>>> times better. To provide this possibility increase the resolution in the
>>> em_perf_state::cost for 64-bit architectures. The costs for increasing
>>> resolution in 32-bit architectures are pretty high (64-bit division) and
>>> the returns do not justify the increased costs.
>
> s/The costs ... increased costs./The cost of increasing resolution on
> 32-bit is pretty high (64-bit division) and is not justified since there
> are no new 32bit big.LITTLE EAS systems expected which would benefit
> from this higher resolution./ ?
Sounds better indeed.
>
>>> This patch allows to avoid the rounding to milli-Watt errors, which might
>>> occur in EAS energy estimation for each Performance Domains (PD). The
>
> s/Performance Domains (PD)/PD.
OK
>
> [...]
>
>>> Scenario:
>>> Low utilized system e.g. ~200 sum_util for PD0 and ~220 for PD1. There
>>> are quite a few small tasks ~10-15 util. These tasks would suffer for
>>> the rounding error. Such system utilization has been seen while playing
>>> some simple games. In such condition our partner reported 5..10mA less
>>> battery drain.
>
> Hard to digest: Maybe s/Such system ... battery drain./These utilization
> values are typical when running games on Android. One of our partners
> has reported 5..10mA less battery drain when running with increased
> resolution./ ?
Sounds good.
>
>>>
>>> Some details:
>>> We have two Perf Domains (PDs): PD0 (big) and PD1 (little)
>
> s/Perf Domains (PDs)/PDs
OK
>
> [...]
>
>>> 2. Difference in the the last find_energy_efficient_cpu(): margin filter.
>
> s/in the the last find_energy_efficient_cpu(): margin filter/in the 6%
> energy margin filter at the end of find_energy_efficient_cpu()/ ?
OK
[snip]
>
> Otherwise, LGTM.
>
> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Thank you Dietmar for the review. I'm going to send the v3.
>
> This is now an EM only patch (Task scheduler (i.e. CFS/EAS) is only
> effected via compute_energy() -> em_cpu_energy().
>
True it's EM only now, so I will ask Rafael to pick it.
prev parent reply other threads:[~2021-08-03 10:08 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-20 9:41 [PATCH v2 0/1] Improve EAS energy estimation and increase precision Lukasz Luba
2021-07-20 9:41 ` [PATCH v2 1/1] PM: EM: Increase energy calculation precision Lukasz Luba
2021-07-20 9:45 ` Greg KH
2021-07-20 10:18 ` Lukasz Luba
2021-08-02 6:21 ` Lukasz Luba
2021-08-03 9:44 ` Dietmar Eggemann
2021-08-03 10:08 ` Lukasz Luba [this message]
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