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

[Juri Lelli <juri.lelli@redhat.com>]

On 09/04/20 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

Hummm, I like the idea, but

> DEFINE_PER_CPU(cpumask_var_t, dl_bw_mask);
> 
> dl_bw_cpus(int i) {

This works if calls are always local to the rd we are interested into
(argument 'i' isn't used). Are we always doing that?

>     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;

What if capacities change between invocations (with the same span)?
Can that happen?

> 
>     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.

Thanks,

Juri