Re: [RFC PATCH] sched: Add scx_cpuperf_target in sched_cpu_util()

[Qais Yousef]

On 03/18/26 13:55, Vincent Guittot wrote:
> On Wed, 18 Mar 2026 at 13:47, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> >
> > On Wed, Mar 18, 2026 at 08:17:55PM +0800, Xuewen Yan wrote:
> > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > index bf948db905ed..20adb6fede2a 100644
> > > --- a/kernel/sched/fair.c
> > > +++ b/kernel/sched/fair.c
> > > @@ -8198,7 +8198,12 @@ unsigned long effective_cpu_util(int cpu, unsigned long util_cfs,
> > >
> > >  unsigned long sched_cpu_util(int cpu)
> > >  {
> > > -     return effective_cpu_util(cpu, cpu_util_cfs(cpu), NULL, NULL);
> > > +     unsigned long util = scx_cpuperf_target(cpu);
> > > +
> > > +     if (!scx_switched_all())
> > > +             util += cpu_util_cfs(cpu);
> > > +
> > > +     return effective_cpu_util(cpu, util, NULL, NULL);
> > >  }
> >
> > This puts the common case of no ext muck into the slow path of that
> > static_branch.
> 
> +1
> I was about to same
> 
> >
> > This wants to be something like:
> >
> > unsigned long sched_cpu_util(int cpu)
> > {
> >         unsigned long util = cpu_util_cfs(cpu);
> >
> >         if (scx_enabled()) {
> >                 unsigned long scx_util = scx_cpuperf_target(cpu);
> 
> also scx_cpuperf_target() does not reflect the utilization of the CPU
> but the targeted perfromance level

Beside that, this sort of plug-and-play is a big concern. You picked up sched
ext and changed the behavior, then you'd need to get your thermal management to
work with that. Not retrospectively sprinkle these hacks around to force things
to work again.

This is a no from me. I think we have to keep the separation clear. And
I haven't seen a single contribution back to scheduler out of these
'experiments'. Clearly everyone is going their own way and getting the
threshold for us to get patches merged even higher not to break these out of
tree 'experiments' is a big nuance. I think the sugov one was already a mistake
to accept.

> 
> 
> >
> >                 if (!scx_switched_all())
> >                         scx_util += util;
> >
> >                 util = scx_util;
> >         }
> >
> >         return effective_cpu_util(cpu, util, NULL, NULL);
> > }