Re: [PATCH RFC 0/8] SCHED_DEADLINE freq/cpu invariance and OPP selection

[Peter Zijlstra]

On Wed, May 24, 2017 at 10:50:53AM +0100, Juri Lelli wrote:

> Agreed. However, problem seems to be that
> 
>  - in my opinion (current implementation) this translated into scaling
>    runtime considering current freq and cpu-max-capacity; and this is
>    required when frequency scaling is enabled and we still want to meet
>    a task's guaranteed bandwidth

Just so. The bandwidth they request is based on instructions/work. We
need to get a certain amount of instructions sorted. Nobody cares we get
an exact 10% at random frequency if they loose they finger because we
didn't get that final instruction out that stops the saw blade.

>  - Luca seemed instead to be inclined to say that, if we scale runtime
>    for !reclaim tasks, such tasks are basically allowed to run for more
>    time (when frequency is lower than max) by using some of the
>    bandwidth not allocated to themselves

Yes, that's a wrong view :-) We don't care about 'time', we care about
getting the instruction stream / work completed.