Messages in this thread | | | Subject | Re: [PATCH v2 4/4] sched/fair: Make feec() consider uclamp restrictions | From | Dietmar Eggemann <> | Date | Tue, 10 Dec 2019 19:23:28 +0100 |
| |
On 03/12/2019 16:59, Valentin Schneider wrote:
Could you replace feec (find_energy_efficient_cpu) with EAS wakeup path in the subject line? The term EAS is described in Documentation/scheduler/sched-energy.rst so its probably easier to match the patch to functionality.
> We've just made task_fits_capacity() uclamp-aware, and > find_energy_efficient_cpu() needs to go through the same treatment. > Things are somewhat different here however - we can't directly use > the now uclamp-aware task_fits_capacity(). Consider the following setup: > > rq.cpu_capacity_orig = 512 > rq.util_avg = 200 > rq.uclamp.max = 768 > > p.util_est = 600 > p.uclamp.max = 256 > > (p not yet enqueued on rq) > > Using task_fits_capacity() here would tell us that p fits on the above CPU. > However, enqueuing p on that CPU *will* cause it to become overutilized > since rq clamp values are max-aggregated, so we'd remain with
I assume it doesn't harm to explicitly mention that this rq.uclamp.max = 768 value comes from another task already enqueued on a cfs_rq of this rq. This gives same substance to the term max-aggregated here.
> rq.uclamp.max = 768 > > Thus we could reach a high enough frequency to reach beyond 0.8 * 512 > utilization (== overutilized). What feec() needs here is
s/feec()/find_energy_efficient_cpu() ?
> uclamp_rq_util_with() which lets us peek at the future utilization > landscape, including rq-wide uclamp values. > > Make find_energy_efficient_cpu() use uclamp_rq_util_with() for its > fits_capacity() check. This is in line with what compute_energy() ends up > using for estimating utilization.
This is also aligned with schedutil_cpu_util() (you do mention this in the code later in this patch.
[...]
| |