Re: [PATCH 2/4] sched/deadline: Improve admission control for asymmetric CPU capacities

Qais Yousef
2020-04-14T11:40:47Z

On 04/09/20 19:29, Dietmar Eggemann wrote:

[...]

> Maybe we can do a hybrid. We have rd->span and rd->sum_cpu_capacity and
> with the help of an extra per-cpu cpumask we could just
>
> DEFINE_PER_CPU(cpumask_var_t, dl_bw_mask);
>
> dl_bw_cpus(int i) {
>
> struct cpumask *cpus = this_cpu_cpumask_var_ptr(dl_bw_mask);
> ...
> cpumask_and(cpus, rd->span, cpu_active_mask);
>
> return cpumask_weight(cpus);
> }
>
> and
>
> dl_bw_capacity(int i) {
>
> struct cpumask *cpus = this_cpu_cpumask_var_ptr(dl_bw_mask);
> ...
> cpumask_and(cpus, rd->span, cpu_active_mask);
> if (cpumask_equal(cpus, rd->span))
> return rd->sum_cpu_capacity;
>
> for_each_cpu(i, cpus)
> cap += capacity_orig_of(i);
>
> return cap;
> }
>
> So only in cases in which rd->span and cpu_active_mask differ we would
> have to sum up again.

I haven't followed this discussion closely, so I could be missing something
here.

In sched_cpu_dying() we call set_rq_offline() which clears the cpu in
rq->rd->online.

So the way I read the code

rd->online = cpumask_and(rd->span, cpu_active_mask)

But I could have easily missed some detail.

Regardless, it seems to me that DL is working around something not right in the
definition of rd->span or using the wrong variable.

My 2p :-). I have to go back and read the discussion in more detail.

Thanks

--
Qais Yousef