arm64: dts: qcom: sdm845: correct dynamic power coefficients
authorVincent Guittot <vincent.guittot@linaro.org>
Fri, 6 Jan 2023 16:46:18 +0000 (17:46 +0100)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Thu, 11 May 2023 14:03:09 +0000 (23:03 +0900)
commit44018ad5f230f5147aee4e66c46f26a1d8bdcff3
treee98d1aae0b34827ef9365eebfd8f5830286ae704
parent7cb0802954769575918251567cdd3e59142ef3bd
arm64: dts: qcom: sdm845: correct dynamic power coefficients

[ Upstream commit 44750f153699b6e4f851a399287e5c8df208d696 ]

While stressing EAS on my dragonboard RB3, I have noticed that LITTLE cores
where never selected as the most energy efficient CPU whatever the
utilization level of waking task.

energy model framework uses its cost field to estimate the energy with
the formula:

  nrg = cost of the selected OPP * utilization / CPU's max capacity

which ends up selecting the CPU with lowest cost / max capacity ration
as long as the utilization fits in the OPP's capacity.

If we compare the cost of a little OPP with similar capacity of a big OPP
like :
       OPP(kHz)   OPP capacity    cost     max capacity   cost/max capacity
LITTLE 1766400    407             351114   407            863
big    1056000    408             520267   1024           508

This can be interpreted as the LITTLE core consumes 70% more than big core
for the same compute capacity.

According to [1], LITTLE consumes 10% less than big core for Coremark
benchmark at those OPPs. If we consider that everything else stays
unchanged, the dynamic-power-coefficient of LITTLE core should be
only 53% of the current value: 290 * 53% = 154

Set the dynamic-power-coefficient of CPU0-3 to 154 to fix the energy model.

[1] https://github.com/kdrag0n/freqbench/tree/master/results/sdm845/main

Fixes: 0e0a8e35d725 ("arm64: dts: qcom: sdm845: correct dynamic power coefficients")
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230106164618.1845281-1-vincent.guittot@linaro.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
arch/arm64/boot/dts/qcom/sdm845.dtsi