• Vincent Guittot's avatar
    arm64: dts: qcom: sdm845: correct dynamic power coefficients · 44750f15
    Vincent Guittot authored
    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: 0e0a8e35 ("arm64: dts: qcom: sdm845: correct dynamic power coefficients")
    Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
    Signed-off-by: default avatarBjorn Andersson <andersson@kernel.org>
    Link: https://lore.kernel.org/r/20230106164618.1845281-1-vincent.guittot@linaro.org
    44750f15
sdm845.dtsi 142 KB