Re: [RFC 1/8] sched: Add nice value change notifier

[Barry Song <21cnbao@gmail.com>]

On Wed, Oct 6, 2021 at 5:15 PM Wanghui (John) <john.wanghui@huawei.com> wrote:
>
> HI Tvrtko
>
> On 2021/10/4 22:36, Tvrtko Ursulin wrote:
> >   void set_user_nice(struct task_struct *p, long nice)
> >   {
> >       bool queued, running;
> > -     int old_prio;
> > +     int old_prio, ret;
> >       struct rq_flags rf;
> >       struct rq *rq;
> >
> > @@ -6915,6 +6947,9 @@ void set_user_nice(struct task_struct *p, long nice)
> >
> >   out_unlock:
> >       task_rq_unlock(rq, p, &rf);
> > +
> > +     ret = atomic_notifier_call_chain(&user_nice_notifier_list, nice, p);
> > +     WARN_ON_ONCE(ret != NOTIFY_DONE);
> >   }
> How about adding a new "io_nice" to task_struct，and move the call chain to
> sched_setattr/getattr, there are two benefits:

We already have an ionice for block io scheduler. hardly can this new io_nice
be generic to all I/O. it seems the patchset is trying to link
process' nice with
GPU's scheduler, to some extent, it makes more senses than having a
common ionice because we have a lot of IO devices in the systems, we don't
know which I/O the ionice of task_struct should be applied to.

Maybe we could have an ionice dedicated for GPU just like ionice for CFQ
of bio/request scheduler.

>
> 1. Decoupled with fair scheduelr. In our use case, high priority tasks often
>     use rt scheduler.

Is it possible to tell GPU RT as we are telling them CFS nice?

> 2. The range of value don't need to be bound to -20~19 or 0~139
>

could build a mapping between the priorities of process and GPU. It seems
not a big deal.

Thanks
barry