Re: [PATCH v2 1/1] PM: EM: Increase energy calculation precision

From: Lukasz Luba
Date: Tue Aug 03 2021 - 06:08:40 EST

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
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.



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



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()/ ?



Otherwise, LGTM.

Reviewed-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>

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.