Message ID  1535526518290221gitsendemailvincent.guittot@linaro.org 

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Hi Vincent, Vincent Guittot <vincent.guittot@linaro.org> writes: > The unit of dynamicpowercoefficient is described as mW/MHz/uV^2 whereas > its usage in the code assumes that unit is uW/MHz/V^2 > > In drivers/thermal/cpu_cooling.c, the code is : > > power = (u64)capacitance * freq_mhz * voltage_mv * voltage_mv; > do_div(power, 1000000000); > > which can be summarized as : > power (mW) = capacitance * freq_mhz/1000 * (voltage_mv/1000)^2 > or > power (mW) = (capacitance * freq_mhz * (voltage_mv/1000)^2) / 1000 > then > power (mW) = power (uW) / 1000 > so > power (uW) = capacitance * freq_mhz * (voltage_mv/1000)^2 > > Furthermore, if we test basic values like : > voltage_mv = 1000mV = 1V > freq_mhz = 1000Mhz > > The minimum possible power, when dynamicpowercoefficient equals 1, will > be with current unit: > min power = 1 * 1000 * (1000000)^2 = 10^15 mW > which is not realistic > > With the unit used by the code, the min power is > min power = 1 * 1000 * 1^2 = 1000uW = 1mW which is far more realistic > > Signedoffby: Vincent Guittot <vincent.guittot@linaro.org> Ackedby: Punit Agrawal <punit.agrawal@arm.com> Thanks for fixing the mismatch. >  > Documentation/devicetree/bindings/arm/cpus.txt  4 ++ > 1 file changed, 2 insertions(+), 2 deletions() > > diff git a/Documentation/devicetree/bindings/arm/cpus.txt b/Documentation/devicetree/bindings/arm/cpus.txt > index 29e1dc5..71d8cd0 100644 >  a/Documentation/devicetree/bindings/arm/cpus.txt > +++ b/Documentation/devicetree/bindings/arm/cpus.txt > @@ 274,7 +274,7 @@ described below. > Usage: optional > Value type: <propencodedarray> > Definition: A u32 value that represents the running time dynamic >  power coefficient in units of mW/MHz/uV^2. The > + power coefficient in units of uW/MHz/V^2. The > coefficient can either be calculated from power > measurements or derived by analysis. > > @@ 285,7 +285,7 @@ described below. > > Pdyn = dynamicpowercoefficient * V^2 * f > >  where voltage is in uV, frequency is in MHz. > + where voltage is in V, frequency is in MHz. > > Example 1 (dualcluster big.LITTLE system 32bit):
On 290818, 09:08, Vincent Guittot wrote: > The unit of dynamicpowercoefficient is described as mW/MHz/uV^2 whereas > its usage in the code assumes that unit is uW/MHz/V^2 > > In drivers/thermal/cpu_cooling.c, the code is : > > power = (u64)capacitance * freq_mhz * voltage_mv * voltage_mv; > do_div(power, 1000000000); > > which can be summarized as : > power (mW) = capacitance * freq_mhz/1000 * (voltage_mv/1000)^2 > or > power (mW) = (capacitance * freq_mhz * (voltage_mv/1000)^2) / 1000 > then > power (mW) = power (uW) / 1000 > so > power (uW) = capacitance * freq_mhz * (voltage_mv/1000)^2 > > Furthermore, if we test basic values like : > voltage_mv = 1000mV = 1V > freq_mhz = 1000Mhz > > The minimum possible power, when dynamicpowercoefficient equals 1, will > be with current unit: > min power = 1 * 1000 * (1000000)^2 = 10^15 mW > which is not realistic > > With the unit used by the code, the min power is > min power = 1 * 1000 * 1^2 = 1000uW = 1mW which is far more realistic > > Signedoffby: Vincent Guittot <vincent.guittot@linaro.org> >  > Documentation/devicetree/bindings/arm/cpus.txt  4 ++ > 1 file changed, 2 insertions(+), 2 deletions() Ackedby: Viresh Kumar <viresh.kumar@linaro.org>
On Wed, Aug 29, 2018 at 09:08:38AM +0200, Vincent Guittot wrote: > The unit of dynamicpowercoefficient is described as mW/MHz/uV^2 whereas > its usage in the code assumes that unit is uW/MHz/V^2 > > In drivers/thermal/cpu_cooling.c, the code is : > > power = (u64)capacitance * freq_mhz * voltage_mv * voltage_mv; > do_div(power, 1000000000); > > which can be summarized as : > power (mW) = capacitance * freq_mhz/1000 * (voltage_mv/1000)^2 > or > power (mW) = (capacitance * freq_mhz * (voltage_mv/1000)^2) / 1000 > then > power (mW) = power (uW) / 1000 > so > power (uW) = capacitance * freq_mhz * (voltage_mv/1000)^2 > > Furthermore, if we test basic values like : > voltage_mv = 1000mV = 1V > freq_mhz = 1000Mhz > > The minimum possible power, when dynamicpowercoefficient equals 1, will > be with current unit: > min power = 1 * 1000 * (1000000)^2 = 10^15 mW > which is not realistic > > With the unit used by the code, the min power is > min power = 1 * 1000 * 1^2 = 1000uW = 1mW which is far more realistic > > Signedoffby: Vincent Guittot <vincent.guittot@linaro.org> >  > Documentation/devicetree/bindings/arm/cpus.txt  4 ++ > 1 file changed, 2 insertions(+), 2 deletions() Applied, thanks. Rob
diff git a/Documentation/devicetree/bindings/arm/cpus.txt b/Documentation/devicetree/bindings/arm/cpus.txt index 29e1dc5..71d8cd0 100644  a/Documentation/devicetree/bindings/arm/cpus.txt +++ b/Documentation/devicetree/bindings/arm/cpus.txt @@ 274,7 +274,7 @@ described below. Usage: optional Value type: <propencodedarray> Definition: A u32 value that represents the running time dynamic  power coefficient in units of mW/MHz/uV^2. The + power coefficient in units of uW/MHz/V^2. The coefficient can either be calculated from power measurements or derived by analysis. @@ 285,7 +285,7 @@ described below. Pdyn = dynamicpowercoefficient * V^2 * f  where voltage is in uV, frequency is in MHz. + where voltage is in V, frequency is in MHz. Example 1 (dualcluster big.LITTLE system 32bit):
The unit of dynamicpowercoefficient is described as mW/MHz/uV^2 whereas its usage in the code assumes that unit is uW/MHz/V^2 In drivers/thermal/cpu_cooling.c, the code is : power = (u64)capacitance * freq_mhz * voltage_mv * voltage_mv; do_div(power, 1000000000); which can be summarized as : power (mW) = capacitance * freq_mhz/1000 * (voltage_mv/1000)^2 or power (mW) = (capacitance * freq_mhz * (voltage_mv/1000)^2) / 1000 then power (mW) = power (uW) / 1000 so power (uW) = capacitance * freq_mhz * (voltage_mv/1000)^2 Furthermore, if we test basic values like : voltage_mv = 1000mV = 1V freq_mhz = 1000Mhz The minimum possible power, when dynamicpowercoefficient equals 1, will be with current unit: min power = 1 * 1000 * (1000000)^2 = 10^15 mW which is not realistic With the unit used by the code, the min power is min power = 1 * 1000 * 1^2 = 1000uW = 1mW which is far more realistic Signedoffby: Vincent Guittot <vincent.guittot@linaro.org>  Documentation/devicetree/bindings/arm/cpus.txt  4 ++ 1 file changed, 2 insertions(+), 2 deletions()