Re: [PATCH v6 11/16] sched/fair: Add uclamp support to energy_compute()

Quentin Perret
2019-01-22T12:13:22Z

On Tuesday 15 Jan 2019 at 10:15:08 (+0000), Patrick Bellasi wrote:
> The Energy Aware Scheduler (AES) estimates the energy impact of waking

s/AES/EAS :-)

[...]
> + for_each_cpu_and(cpu, pd_mask, cpu_online_mask) {
> + cfs_util = cpu_util_next(cpu, p, dst_cpu);
> +
> + /*
> + * Busy time computation: utilization clamping is not
> + * required since the ratio (sum_util / cpu_capacity)
> + * is already enough to scale the EM reported power
> + * consumption at the (eventually clamped) cpu_capacity.
> + */

Right.

> + sum_util += schedutil_cpu_util(cpu, cfs_util, cpu_cap,
> + ENERGY_UTIL, NULL);
> +
> + /*
> + * Performance domain frequency: utilization clamping
> + * must be considered since it affects the selection
> + * of the performance domain frequency.
> + */

So that actually affects the way we deal with RT I think. I assume the
idea is to say if you don't want to reflect the RT-go-to-max-freq thing
in EAS (which is what we do now) you should set the min cap for RT to 0.
Is that correct ?

I'm fine with this conceptually but maybe the specific case of RT should
be mentioned somewhere in the commit message or so ? I think it's
important to say that clearly since this patch changes the default
behaviour.

> + cpu_util = schedutil_cpu_util(cpu, cfs_util, cpu_cap,
> + FREQUENCY_UTIL,
> + cpu == dst_cpu ? p : NULL);
> + max_util = max(max_util, cpu_util);
> }
>
> energy += em_pd_energy(pd->em_pd, max_util, sum_util);

Thanks,
Quentin