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Date: Thu, 7 Jul 2022 11:44:55 +0100 From: Lukasz Luba <lukasz.luba@....com> To: Daniel Lezcano <daniel.lezcano@...aro.org> Cc: amitk@...nel.org, rui.zhang@...el.com, viresh.kumar@...aro.org, linux-kernel@...r.kernel.org, rafael@...nel.org, dietmar.eggemann@....com, nm@...com, sboyd@...nel.org, sudeep.holla@....com, cristian.marussi@....com, matthias.bgg@...il.com, linux-mediatek@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org Subject: Re: [PATCH v2 1/4] PM: EM: convert power field to micro-Watts precision and align drivers On 7/7/22 09:31, Daniel Lezcano wrote: > 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@....com> > > Acked-by: Daniel Lezcano <daniel.lezcano@...aro.org> > > > Thanks Daniel! I'll ping Rafael to take this via his PM tree
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