Messages in this thread | | | Date | Thu, 7 Jul 2022 10:31:09 +0200 | Subject | Re: [PATCH v2 1/4] PM: EM: convert power field to micro-Watts precision and align drivers | From | Daniel Lezcano <> |
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On 07/07/2022 09:15, Lukasz Luba wrote: > The milli-Watts precision causes rounding errors while calculating > efficiency cost for each OPP. This is especially visible in the 'simple' > Energy Model (EM), where the power for each OPP is provided from OPP > framework. This can cause some OPPs to be marked inefficient, while > using micro-Watts precision that might not happen. > > Update all EM users which access 'power' field and assume the value is > in milli-Watts. > > Solve also an issue with potential overflow in calculation of energy > estimation on 32bit machine. It's needed now since the power value > (thus the 'cost' as well) are higher. > > Example calculation which shows the rounding error and impact: > > power = 'dyn-power-coeff' * volt_mV * volt_mV * freq_MHz > > power_a_uW = (100 * 600mW * 600mW * 500MHz) / 10^6 = 18000 > power_a_mW = (100 * 600mW * 600mW * 500MHz) / 10^9 = 18 > > power_b_uW = (100 * 605mW * 605mW * 600MHz) / 10^6 = 21961 > power_b_mW = (100 * 605mW * 605mW * 600MHz) / 10^9 = 21 > > max_freq = 2000MHz > > cost_a_mW = 18 * 2000MHz/500MHz = 72 > cost_a_uW = 18000 * 2000MHz/500MHz = 72000 > > cost_b_mW = 21 * 2000MHz/600MHz = 70 // <- artificially better > cost_b_uW = 21961 * 2000MHz/600MHz = 73203 > > The 'cost_b_mW' (which is based on old milli-Watts) is misleadingly > better that the 'cost_b_uW' (this patch uses micro-Watts) and such > would have impact on the 'inefficient OPPs' information in the Cpufreq > framework. This patch set removes the rounding issue. > > Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
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