Re: [RFC PATCH v2 0/6] Energy Aware Scheduling

[Dietmar Eggemann]

Hi Leo,

On 04/17/2018 02:50 PM, Leo Yan wrote:
> Hi Dietmar,
>
> On Fri, Apr 06, 2018 at 04:36:01PM +0100, Dietmar Eggemann wrote:

[...]

> > 1.1 Energy Model
> >
> > A CPU with asymmetric core capacities features cores with significantly
> > different energy and performance characteristics. As the configurations
> > can vary greatly from one SoC to another, designing an energy-efficient
> > scheduling heuristic that performs well on a broad spectrum of platforms
> > appears to be particularly hard.
> > This proposal attempts to solve this issue by providing the scheduler
> > with an energy model of the platform which enables energy impact
> > estimation of scheduling decisions in a generic way. The energy model is
> > kept very simple as it represents only the active power of CPUs at all
> > available P-states and relies on existing data in the kernel (only used
> > by the thermal subsystem so far).
> > This proposal does not include the power consumption of C-states and
> > cluster-level resources which were originally introduced in [1] since
> > firstly, their impact on task placement decisions appears to be
> > neglectable on modern asymmetric platforms and secondly, they require
> > additional infrastructure and data (e.g new DT entries).
>
> Seems to me, if we move forward a bit for the energy model, we can use
> more simple method by generate power consumption:
>
>    Power(@Freq) = Power(cpu_util=100%@Freq) - Power(cpu_util=%0@Freq)
>
>  From upper formula, the power data includes CPU and cluster level
> power (and includes dynamic power and static leakage) but this is
> quite straightforward for measurement.
>
> I read a bit for Quentin's slides for simplized power modeling
> experiments [1], IIUC the simplized power modeling still bases on the
> distinguished CPU and cluster c-state and p-state power data, and just
> select CPU p-state power data for scheduler.  I wander if we can
> simplize the power measurement, so the power data can be generated in
> single one testing and the power data without any post processing.
>
> This might need more detailed experiment to support this idea, just
> want to know how about you guys think for this?
>
> This is a side topic for this patch series, so whatever the conclusion
> for it, I think this will not impact anything of this patch series
> implementation and upstreaming.
>
> [1] http://connect.linaro.org/resource/hkg18/hkg18-501/

The simplified Energy Model in this patch-set only contains the per-cpu 
p-state power data. This allows us to only rely on the knowledge of 
which OPP's (opp frequency/max frequency) we have for the individual 
frequency domains and the CPU dt property 'dynamic-power-coefficient'. 
This is even encapsulated in the new PM_OPP library function 
dev_pm_opp_get_power().

Please note that this has to be redesigned since neither Rafael nor 
Peter like the idea of using PM_OPP library here. But we will continue 
to only use per-cpu p-state power data.

[...]

> > 30 iterations of perf bench sched messaging --pipe --thread --group G
> > --loop L with G=[1 2 4 8] and L=50000 (Hikey960)/16000 (Juno r0).
>
> What's the reason to select different loop number for Hikey960 and
> Juno? Based on the testing time?

The Juno r0 board has only ~0.3 of the performance of the Hikey960. We 
wanted to have roughly comparable test execution time numbers. We're 
only interested in the difference between running w/ and w/o this code 
per platform.