| Message ID | 20200929121610.16060-1-lukasz.luba@arm.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | [1/2] docs: Clarify abstract scale usage for power values in Energy Model | expand |
Hi, On Tue, Sep 29, 2020 at 5:16 AM Lukasz Luba <lukasz.luba@arm.com> wrote: > > The Energy Model (EM) can store power values in milli-Watts or in abstract > scale. This might cause issues in the subsystems which use the EM for > estimating the device power, such as: > - mixing of different scales in a subsystem which uses multiple > (cooling) devices (e.g. thermal Intelligent Power Allocation (IPA)) > - assuming that energy [milli-Joules] can be derived from the EM power > values which might not be possible since the power scale doesn't have to > be in milli-Watts > > To avoid misconfiguration add the needed documentation to the EM and > related subsystems: EAS and IPA. > > Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> > --- > .../driver-api/thermal/power_allocator.rst | 8 ++++++++ > Documentation/power/energy-model.rst | 13 +++++++++++++ > Documentation/scheduler/sched-energy.rst | 5 +++++ > 3 files changed, 26 insertions(+) I haven't read through these files in massive detail, but the quick skim makes me believe that your additions seem sane. In general, I'm happy with documenting reality, thus: Reviewed-by: Douglas Anderson <dianders@chromium.org> I will note: you haven't actually updated the device tree bindings. Thus, presumably, anyone who is specifying these numbers in the device tree is still supposed to specify them in a way that mW can be recovered, right? Said another way: nothing about your patches makes it OK to specify numbers in device trees using an "abstract scale", right? -Doug
Hi Douglas, On 9/30/20 12:53 AM, Doug Anderson wrote: > Hi, > > On Tue, Sep 29, 2020 at 5:16 AM Lukasz Luba <lukasz.luba@arm.com> wrote: >> >> The Energy Model (EM) can store power values in milli-Watts or in abstract >> scale. This might cause issues in the subsystems which use the EM for >> estimating the device power, such as: >> - mixing of different scales in a subsystem which uses multiple >> (cooling) devices (e.g. thermal Intelligent Power Allocation (IPA)) >> - assuming that energy [milli-Joules] can be derived from the EM power >> values which might not be possible since the power scale doesn't have to >> be in milli-Watts >> >> To avoid misconfiguration add the needed documentation to the EM and >> related subsystems: EAS and IPA. >> >> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> >> --- >> .../driver-api/thermal/power_allocator.rst | 8 ++++++++ >> Documentation/power/energy-model.rst | 13 +++++++++++++ >> Documentation/scheduler/sched-energy.rst | 5 +++++ >> 3 files changed, 26 insertions(+) > > I haven't read through these files in massive detail, but the quick > skim makes me believe that your additions seem sane. In general, I'm > happy with documenting reality, thus: > > Reviewed-by: Douglas Anderson <dianders@chromium.org> Thank you for the review. > > I will note: you haven't actually updated the device tree bindings. > Thus, presumably, anyone who is specifying these numbers in the device > tree is still supposed to specify them in a way that mW can be > recovered, right? Said another way: nothing about your patches makes > it OK to specify numbers in device trees using an "abstract scale", > right? For completeness, we are talking here about the binding from: Documentation/devicetree/bindings/arm/cpus.yaml which is 'dynamic-power-coefficient'. Yes, it stays untouched, also the unit (uW/MHz/V^2) which then allows to have mW in the power values in the EM. Regards, Lukasz
On 9/30/2020 1:55 PM, Lukasz Luba wrote: > Hi Douglas, > > On 9/30/20 12:53 AM, Doug Anderson wrote: >> Hi, >> >> On Tue, Sep 29, 2020 at 5:16 AM Lukasz Luba <lukasz.luba@arm.com> wrote: >>> >>> The Energy Model (EM) can store power values in milli-Watts or in abstract >>> scale. This might cause issues in the subsystems which use the EM for >>> estimating the device power, such as: >>> - mixing of different scales in a subsystem which uses multiple >>> (cooling) devices (e.g. thermal Intelligent Power Allocation (IPA)) >>> - assuming that energy [milli-Joules] can be derived from the EM power >>> values which might not be possible since the power scale doesn't have to >>> be in milli-Watts >>> >>> To avoid misconfiguration add the needed documentation to the EM and >>> related subsystems: EAS and IPA. >>> >>> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> >>> --- >>> .../driver-api/thermal/power_allocator.rst | 8 ++++++++ >>> Documentation/power/energy-model.rst | 13 +++++++++++++ >>> Documentation/scheduler/sched-energy.rst | 5 +++++ >>> 3 files changed, 26 insertions(+) >> >> I haven't read through these files in massive detail, but the quick >> skim makes me believe that your additions seem sane. In general, I'm >> happy with documenting reality, thus: >> >> Reviewed-by: Douglas Anderson <dianders@chromium.org> > > Thank you for the review. > >> >> I will note: you haven't actually updated the device tree bindings. >> Thus, presumably, anyone who is specifying these numbers in the device >> tree is still supposed to specify them in a way that mW can be >> recovered, right? Said another way: nothing about your patches makes >> it OK to specify numbers in device trees using an "abstract scale", >> right? > > For completeness, we are talking here about the binding from: > Documentation/devicetree/bindings/arm/cpus.yaml > which is 'dynamic-power-coefficient'. Yes, it stays untouched, also the > unit (uW/MHz/V^2) which then allows to have mW in the power > values in the EM. So for platforms where 'dynamic-power-coefficient' is specified in device tree, its always expected to be derived from 'real' power numbers on these platforms in 'real' mW? Atleast on Qualcomm platforms we have these numbers scaled, so in essence it can't be used to derive 'real' mW values. That said we also do not have any of the 'platform might face potential issue of mixing devices in one thermal zone of two scales' problem. So the question is, can such platforms still use 'dynamic-power-coefficient' in device tree and create an abstract scale? The other way of doing this would be to *not* specify this value in device tree and have these values stored in the cpufreq driver and register a custom callback to do the math. It just feels like jumping through hoops just to deal with the fact that the device tree bindings say its expected to be in mW and can't be abstract.
On 9/30/20 11:55 AM, Rajendra Nayak wrote: > > On 9/30/2020 1:55 PM, Lukasz Luba wrote: >> Hi Douglas, >> >> On 9/30/20 12:53 AM, Doug Anderson wrote: >>> Hi, >>> >>> On Tue, Sep 29, 2020 at 5:16 AM Lukasz Luba <lukasz.luba@arm.com> wrote: >>>> >>>> The Energy Model (EM) can store power values in milli-Watts or in >>>> abstract >>>> scale. This might cause issues in the subsystems which use the EM for >>>> estimating the device power, such as: >>>> - mixing of different scales in a subsystem which uses multiple >>>> (cooling) devices (e.g. thermal Intelligent Power Allocation (IPA)) >>>> - assuming that energy [milli-Joules] can be derived from the EM power >>>> values which might not be possible since the power scale doesn't >>>> have to >>>> be in milli-Watts >>>> >>>> To avoid misconfiguration add the needed documentation to the EM and >>>> related subsystems: EAS and IPA. >>>> >>>> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> >>>> --- >>>> .../driver-api/thermal/power_allocator.rst | 8 ++++++++ >>>> Documentation/power/energy-model.rst | 13 >>>> +++++++++++++ >>>> Documentation/scheduler/sched-energy.rst | 5 +++++ >>>> 3 files changed, 26 insertions(+) >>> >>> I haven't read through these files in massive detail, but the quick >>> skim makes me believe that your additions seem sane. In general, I'm >>> happy with documenting reality, thus: >>> >>> Reviewed-by: Douglas Anderson <dianders@chromium.org> >> >> Thank you for the review. >> >>> >>> I will note: you haven't actually updated the device tree bindings. >>> Thus, presumably, anyone who is specifying these numbers in the device >>> tree is still supposed to specify them in a way that mW can be >>> recovered, right? Said another way: nothing about your patches makes >>> it OK to specify numbers in device trees using an "abstract scale", >>> right? >> >> For completeness, we are talking here about the binding from: >> Documentation/devicetree/bindings/arm/cpus.yaml >> which is 'dynamic-power-coefficient'. Yes, it stays untouched, also the >> unit (uW/MHz/V^2) which then allows to have mW in the power >> values in the EM. > > So for platforms where 'dynamic-power-coefficient' is specified in > device tree, > its always expected to be derived from 'real' power numbers on these > platforms in > 'real' mW? Yes, the purpose and the name of that binding was only for 'real' power in mW. > > Atleast on Qualcomm platforms we have these numbers scaled, so in > essence it > can't be used to derive 'real' mW values. That said we also do not have > any of > the 'platform might face potential issue of mixing devices in one > thermal zone > of two scales' problem. If you have these numbers scaled, then it's probably documented somewhere in your docs for your OEMs, because they might assume it's in uW/MHz/V^2 (according to the bindings doc). If not, they probably realized it during the measurements and comparison (that the power in EM is not what they see on the power meter). This binding actually helps those developers who take the experiments and based on measured power values, store derived coefficient. Everyone can just measure in local setup and compare the results easily, speaking the same language (proposing maybe a patch adjusting the value in DT). > > So the question is, can such platforms still use > 'dynamic-power-coefficient' > in device tree and create an abstract scale? The other way of doing this > would > be to *not* specify this value in device tree and have these values > stored in the > cpufreq driver and register a custom callback to do the math. But then we would also have to change the name of that binding. I'd recommend you the second way that you've described. It will avoid your OEMs confusion. In your cpufreq driver you can simply register to EM using the em_dev_register_perf_domain(). In your local callback you can do whatever you need (read driver array, firmware, DT, scale or not, etc). The helper code in dev_pm_opp_of_register_em() is probably not suited for your use case (when you don't want to share the real power of the SoC). > > It just feels like jumping through hoops just to deal with the fact that > the > device tree bindings say its expected to be in mW and can't be abstract. > I don't want to add more confusion into the EM power values topic. Overloading the meaning of that binding would create more mess. Regards, Lukasz
On 9/30/2020 7:34 PM, Lukasz Luba wrote: > > > On 9/30/20 11:55 AM, Rajendra Nayak wrote: >> >> On 9/30/2020 1:55 PM, Lukasz Luba wrote: >>> Hi Douglas, >>> >>> On 9/30/20 12:53 AM, Doug Anderson wrote: >>>> Hi, >>>> >>>> On Tue, Sep 29, 2020 at 5:16 AM Lukasz Luba <lukasz.luba@arm.com> wrote: >>>>> >>>>> The Energy Model (EM) can store power values in milli-Watts or in abstract >>>>> scale. This might cause issues in the subsystems which use the EM for >>>>> estimating the device power, such as: >>>>> - mixing of different scales in a subsystem which uses multiple >>>>> (cooling) devices (e.g. thermal Intelligent Power Allocation (IPA)) >>>>> - assuming that energy [milli-Joules] can be derived from the EM power >>>>> values which might not be possible since the power scale doesn't have to >>>>> be in milli-Watts >>>>> >>>>> To avoid misconfiguration add the needed documentation to the EM and >>>>> related subsystems: EAS and IPA. >>>>> >>>>> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> >>>>> --- >>>>> .../driver-api/thermal/power_allocator.rst | 8 ++++++++ >>>>> Documentation/power/energy-model.rst | 13 +++++++++++++ >>>>> Documentation/scheduler/sched-energy.rst | 5 +++++ >>>>> 3 files changed, 26 insertions(+) >>>> >>>> I haven't read through these files in massive detail, but the quick >>>> skim makes me believe that your additions seem sane. In general, I'm >>>> happy with documenting reality, thus: >>>> >>>> Reviewed-by: Douglas Anderson <dianders@chromium.org> >>> >>> Thank you for the review. >>> >>>> >>>> I will note: you haven't actually updated the device tree bindings. >>>> Thus, presumably, anyone who is specifying these numbers in the device >>>> tree is still supposed to specify them in a way that mW can be >>>> recovered, right? Said another way: nothing about your patches makes >>>> it OK to specify numbers in device trees using an "abstract scale", >>>> right? >>> >>> For completeness, we are talking here about the binding from: >>> Documentation/devicetree/bindings/arm/cpus.yaml >>> which is 'dynamic-power-coefficient'. Yes, it stays untouched, also the >>> unit (uW/MHz/V^2) which then allows to have mW in the power >>> values in the EM. >> >> So for platforms where 'dynamic-power-coefficient' is specified in device tree, >> its always expected to be derived from 'real' power numbers on these platforms in >> 'real' mW? > > Yes, the purpose and the name of that binding was only for 'real' > power in mW. > >> >> Atleast on Qualcomm platforms we have these numbers scaled, so in essence it >> can't be used to derive 'real' mW values. That said we also do not have any of >> the 'platform might face potential issue of mixing devices in one thermal zone >> of two scales' problem. > > If you have these numbers scaled, then it's probably documented > somewhere in your docs for your OEMs, because they might assume it's in > uW/MHz/V^2 (according to the bindings doc). If not, they probably > realized it during the measurements and comparison (that the power in > EM is not what they see on the power meter). > This binding actually helps those developers who take the experiments > and based on measured power values, store derived coefficient. > Everyone can just measure in local setup and compare the results > easily, speaking the same language (proposing maybe a patch adjusting > the value in DT). > >> >> So the question is, can such platforms still use 'dynamic-power-coefficient' >> in device tree and create an abstract scale? The other way of doing this would >> be to *not* specify this value in device tree and have these values stored in the >> cpufreq driver and register a custom callback to do the math. > > But then we would also have to change the name of that binding. > > I'd recommend you the second way that you've described. It will avoid > your OEMs confusion. In your cpufreq driver you can simply register > to EM using the em_dev_register_perf_domain(). In your local > callback you can do whatever you need (read driver array, firmware, > DT, scale or not, etc). > The helper code in dev_pm_opp_of_register_em() is probably not suited > for your use case (when you don't want to share the real power of the > SoC). Got it, thanks for the clarification. I will get the cpufreq driver updated to use em_dev_register_perf_domain() with a custom callback and get rid of these values from device tree.
Hi, On Wed, Sep 30, 2020 at 8:48 AM Rajendra Nayak <rnayak@codeaurora.org> wrote: > > > On 9/30/2020 7:34 PM, Lukasz Luba wrote: > > > > > > On 9/30/20 11:55 AM, Rajendra Nayak wrote: > >> > >> On 9/30/2020 1:55 PM, Lukasz Luba wrote: > >>> Hi Douglas, > >>> > >>> On 9/30/20 12:53 AM, Doug Anderson wrote: > >>>> Hi, > >>>> > >>>> On Tue, Sep 29, 2020 at 5:16 AM Lukasz Luba <lukasz.luba@arm.com> wrote: > >>>>> > >>>>> The Energy Model (EM) can store power values in milli-Watts or in abstract > >>>>> scale. This might cause issues in the subsystems which use the EM for > >>>>> estimating the device power, such as: > >>>>> - mixing of different scales in a subsystem which uses multiple > >>>>> (cooling) devices (e.g. thermal Intelligent Power Allocation (IPA)) > >>>>> - assuming that energy [milli-Joules] can be derived from the EM power > >>>>> values which might not be possible since the power scale doesn't have to > >>>>> be in milli-Watts > >>>>> > >>>>> To avoid misconfiguration add the needed documentation to the EM and > >>>>> related subsystems: EAS and IPA. > >>>>> > >>>>> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> > >>>>> --- > >>>>> .../driver-api/thermal/power_allocator.rst | 8 ++++++++ > >>>>> Documentation/power/energy-model.rst | 13 +++++++++++++ > >>>>> Documentation/scheduler/sched-energy.rst | 5 +++++ > >>>>> 3 files changed, 26 insertions(+) > >>>> > >>>> I haven't read through these files in massive detail, but the quick > >>>> skim makes me believe that your additions seem sane. In general, I'm > >>>> happy with documenting reality, thus: > >>>> > >>>> Reviewed-by: Douglas Anderson <dianders@chromium.org> > >>> > >>> Thank you for the review. > >>> > >>>> > >>>> I will note: you haven't actually updated the device tree bindings. > >>>> Thus, presumably, anyone who is specifying these numbers in the device > >>>> tree is still supposed to specify them in a way that mW can be > >>>> recovered, right? Said another way: nothing about your patches makes > >>>> it OK to specify numbers in device trees using an "abstract scale", > >>>> right? > >>> > >>> For completeness, we are talking here about the binding from: > >>> Documentation/devicetree/bindings/arm/cpus.yaml > >>> which is 'dynamic-power-coefficient'. Yes, it stays untouched, also the > >>> unit (uW/MHz/V^2) which then allows to have mW in the power > >>> values in the EM. > >> > >> So for platforms where 'dynamic-power-coefficient' is specified in device tree, > >> its always expected to be derived from 'real' power numbers on these platforms in > >> 'real' mW? > > > > Yes, the purpose and the name of that binding was only for 'real' > > power in mW. > > > >> > >> Atleast on Qualcomm platforms we have these numbers scaled, so in essence it > >> can't be used to derive 'real' mW values. That said we also do not have any of > >> the 'platform might face potential issue of mixing devices in one thermal zone > >> of two scales' problem. > > > > If you have these numbers scaled, then it's probably documented > > somewhere in your docs for your OEMs, because they might assume it's in > > uW/MHz/V^2 (according to the bindings doc). If not, they probably > > realized it during the measurements and comparison (that the power in > > EM is not what they see on the power meter). > > This binding actually helps those developers who take the experiments > > and based on measured power values, store derived coefficient. > > Everyone can just measure in local setup and compare the results > > easily, speaking the same language (proposing maybe a patch adjusting > > the value in DT). > > > >> > >> So the question is, can such platforms still use 'dynamic-power-coefficient' > >> in device tree and create an abstract scale? The other way of doing this would > >> be to *not* specify this value in device tree and have these values stored in the > >> cpufreq driver and register a custom callback to do the math. > > > > But then we would also have to change the name of that binding. > > > > I'd recommend you the second way that you've described. It will avoid > > your OEMs confusion. In your cpufreq driver you can simply register > > to EM using the em_dev_register_perf_domain(). In your local > > callback you can do whatever you need (read driver array, firmware, > > DT, scale or not, etc). > > The helper code in dev_pm_opp_of_register_em() is probably not suited > > for your use case (when you don't want to share the real power of the > > SoC). > > Got it, thanks for the clarification. I will get the cpufreq driver updated > to use em_dev_register_perf_domain() with a custom callback and get rid of these > values from device tree. This sounds good. ...except... How exactly are boards supposed to provide their "sustainable-power" number in this model? As far as I'm aware, there's no place to specify this board-specific file other than in device tree, and the bindings [1] say that this value has to be in mW. Lukasz: how do you envision boards can provide "sustainable-power" in cases where the energy model is in "abstract scale"? [1] Documentation/devicetree/bindings/thermal/thermal-zones.yaml -Doug
Hi Douglas On 9/30/20 6:24 PM, Doug Anderson wrote: > Hi, > > On Wed, Sep 30, 2020 at 8:48 AM Rajendra Nayak <rnayak@codeaurora.org> wrote: >> >> >> On 9/30/2020 7:34 PM, Lukasz Luba wrote: >>> >>> >>> On 9/30/20 11:55 AM, Rajendra Nayak wrote: >>>> >>>> On 9/30/2020 1:55 PM, Lukasz Luba wrote: >>>>> Hi Douglas, >>>>> >>>>> On 9/30/20 12:53 AM, Doug Anderson wrote: >>>>>> Hi, >>>>>> >>>>>> On Tue, Sep 29, 2020 at 5:16 AM Lukasz Luba <lukasz.luba@arm.com> wrote: >>>>>>> >>>>>>> The Energy Model (EM) can store power values in milli-Watts or in abstract >>>>>>> scale. This might cause issues in the subsystems which use the EM for >>>>>>> estimating the device power, such as: >>>>>>> - mixing of different scales in a subsystem which uses multiple >>>>>>> (cooling) devices (e.g. thermal Intelligent Power Allocation (IPA)) >>>>>>> - assuming that energy [milli-Joules] can be derived from the EM power >>>>>>> values which might not be possible since the power scale doesn't have to >>>>>>> be in milli-Watts >>>>>>> >>>>>>> To avoid misconfiguration add the needed documentation to the EM and >>>>>>> related subsystems: EAS and IPA. >>>>>>> >>>>>>> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> >>>>>>> --- >>>>>>> .../driver-api/thermal/power_allocator.rst | 8 ++++++++ >>>>>>> Documentation/power/energy-model.rst | 13 +++++++++++++ >>>>>>> Documentation/scheduler/sched-energy.rst | 5 +++++ >>>>>>> 3 files changed, 26 insertions(+) >>>>>> >>>>>> I haven't read through these files in massive detail, but the quick >>>>>> skim makes me believe that your additions seem sane. In general, I'm >>>>>> happy with documenting reality, thus: >>>>>> >>>>>> Reviewed-by: Douglas Anderson <dianders@chromium.org> >>>>> >>>>> Thank you for the review. >>>>> >>>>>> >>>>>> I will note: you haven't actually updated the device tree bindings. >>>>>> Thus, presumably, anyone who is specifying these numbers in the device >>>>>> tree is still supposed to specify them in a way that mW can be >>>>>> recovered, right? Said another way: nothing about your patches makes >>>>>> it OK to specify numbers in device trees using an "abstract scale", >>>>>> right? >>>>> >>>>> For completeness, we are talking here about the binding from: >>>>> Documentation/devicetree/bindings/arm/cpus.yaml >>>>> which is 'dynamic-power-coefficient'. Yes, it stays untouched, also the >>>>> unit (uW/MHz/V^2) which then allows to have mW in the power >>>>> values in the EM. >>>> >>>> So for platforms where 'dynamic-power-coefficient' is specified in device tree, >>>> its always expected to be derived from 'real' power numbers on these platforms in >>>> 'real' mW? >>> >>> Yes, the purpose and the name of that binding was only for 'real' >>> power in mW. >>> >>>> >>>> Atleast on Qualcomm platforms we have these numbers scaled, so in essence it >>>> can't be used to derive 'real' mW values. That said we also do not have any of >>>> the 'platform might face potential issue of mixing devices in one thermal zone >>>> of two scales' problem. >>> >>> If you have these numbers scaled, then it's probably documented >>> somewhere in your docs for your OEMs, because they might assume it's in >>> uW/MHz/V^2 (according to the bindings doc). If not, they probably >>> realized it during the measurements and comparison (that the power in >>> EM is not what they see on the power meter). >>> This binding actually helps those developers who take the experiments >>> and based on measured power values, store derived coefficient. >>> Everyone can just measure in local setup and compare the results >>> easily, speaking the same language (proposing maybe a patch adjusting >>> the value in DT). >>> >>>> >>>> So the question is, can such platforms still use 'dynamic-power-coefficient' >>>> in device tree and create an abstract scale? The other way of doing this would >>>> be to *not* specify this value in device tree and have these values stored in the >>>> cpufreq driver and register a custom callback to do the math. >>> >>> But then we would also have to change the name of that binding. >>> >>> I'd recommend you the second way that you've described. It will avoid >>> your OEMs confusion. In your cpufreq driver you can simply register >>> to EM using the em_dev_register_perf_domain(). In your local >>> callback you can do whatever you need (read driver array, firmware, >>> DT, scale or not, etc). >>> The helper code in dev_pm_opp_of_register_em() is probably not suited >>> for your use case (when you don't want to share the real power of the >>> SoC). >> >> Got it, thanks for the clarification. I will get the cpufreq driver updated >> to use em_dev_register_perf_domain() with a custom callback and get rid of these >> values from device tree. > > This sounds good. ...except... > > How exactly are boards supposed to provide their "sustainable-power" > number in this model? As far as I'm aware, there's no place to > specify this board-specific file other than in device tree, and the > bindings [1] say that this value has to be in mW. Lukasz: how do you > envision boards can provide "sustainable-power" in cases where the > energy model is in "abstract scale"? > > [1] Documentation/devicetree/bindings/thermal/thermal-zones.yaml > I am currently investigating this issue. I will keep you in CC list when I send some patches. Regards, Lukasz
diff --git a/Documentation/driver-api/thermal/power_allocator.rst b/Documentation/driver-api/thermal/power_allocator.rst index 67b6a3297238..5e04553ded5f 100644 --- a/Documentation/driver-api/thermal/power_allocator.rst +++ b/Documentation/driver-api/thermal/power_allocator.rst @@ -269,3 +269,11 @@ won't be very good. Note that this is not particular to this governor, step-wise will also misbehave if you call its throttle() faster than the normal thermal framework tick (due to interrupts for example) as it will overreact. + +Energy Model requirements +========================= + +Another important thing is the consistent scale of the power values +provided by the cooling devices. All of the cooling devices in a single +thermal zone should have power values reported either in milli-Watts +or scaled to the same 'abstract scale'. diff --git a/Documentation/power/energy-model.rst b/Documentation/power/energy-model.rst index a6fb986abe3c..ba7aa581b307 100644 --- a/Documentation/power/energy-model.rst +++ b/Documentation/power/energy-model.rst @@ -20,6 +20,19 @@ possible source of information on its own, the EM framework intervenes as an abstraction layer which standardizes the format of power cost tables in the kernel, hence enabling to avoid redundant work. +The power values might be expressed in milli-Watts or in an 'abstract scale'. +Multiple subsystems might use the EM and it is up to the system integrator to +check that the requirements for the power value scale types are met. An example +can be found in the Energy-Aware Scheduler documentation +Documentation/scheduler/sched-energy.rst. For some subsystems like thermal or +powercap power values expressed in an 'abstract scale' might cause issues. +These subsystems are more interested in estimation of power used in the past, +thus the real milli-Watts might be needed. An example of these requirements can +be found in the Intelligent Power Allocation in +Documentation/driver-api/thermal/power_allocator.rst. +Important thing to keep in mind is that when the power values are expressed in +an 'abstract scale' deriving real energy in milli-Joules would not be possible. + The figure below depicts an example of drivers (Arm-specific here, but the approach is applicable to any architecture) providing power costs to the EM framework, and interested clients reading the data from it:: diff --git a/Documentation/scheduler/sched-energy.rst b/Documentation/scheduler/sched-energy.rst index 001e09c95e1d..afe02d394402 100644 --- a/Documentation/scheduler/sched-energy.rst +++ b/Documentation/scheduler/sched-energy.rst @@ -350,6 +350,11 @@ independent EM framework in Documentation/power/energy-model.rst. Please also note that the scheduling domains need to be re-built after the EM has been registered in order to start EAS. +EAS uses the EM to make a forecasting decision on energy usage and thus it is +more focused on the difference when checking possible options for task +placement. For EAS it doesn't matter whether the EM power values are expressed +in milli-Watts or in an 'abstract scale'. + 6.3 - Energy Model complexity ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The Energy Model (EM) can store power values in milli-Watts or in abstract scale. This might cause issues in the subsystems which use the EM for estimating the device power, such as: - mixing of different scales in a subsystem which uses multiple (cooling) devices (e.g. thermal Intelligent Power Allocation (IPA)) - assuming that energy [milli-Joules] can be derived from the EM power values which might not be possible since the power scale doesn't have to be in milli-Watts To avoid misconfiguration add the needed documentation to the EM and related subsystems: EAS and IPA. Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> --- .../driver-api/thermal/power_allocator.rst | 8 ++++++++ Documentation/power/energy-model.rst | 13 +++++++++++++ Documentation/scheduler/sched-energy.rst | 5 +++++ 3 files changed, 26 insertions(+)