linux-kernel - Re: [PATCH v2 sched_ext/for-6.13] sched_ext: Do not enable LLC/NUMA optimizations when domains overlap

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Message-ID: <Zy0zBsabOT6uAr6V@gpd3>
Date: Thu, 7 Nov 2024 22:37:10 +0100
From: Andrea Righi <arighi@...dia.com>
To: Tejun Heo <tj@...nel.org>
Cc: David Vernet <void@...ifault.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 sched_ext/for-6.13] sched_ext: Do not enable LLC/NUMA
 optimizations when domains overlap

On Thu, Nov 07, 2024 at 09:14:07PM +0100, Andrea Righi wrote:
> On Thu, Nov 07, 2024 at 09:04:56AM -1000, Tejun Heo wrote:
> > Hello, Andrea.
> > 
> > Some nits below:
> > 
> > On Thu, Nov 07, 2024 at 09:48:03AM +0100, Andrea Righi wrote:
> > > +static bool llc_and_numa_mismatch(void)
> > > +{
> > ...
> > > +     for_each_online_cpu(cpu) {
> > > +             sd = cpu_rq(cpu)->sd;
> > > +
> > > +             while (sd) {
> > 
> > This can be for_each_domain(cpu, sd).
> 
> Oh that's nicer, thanks!
> 
> > 
> > > +                     bool is_llc = sd->flags & SD_SHARE_LLC;
> > > +                     bool is_numa = sd->flags & SD_NUMA;
> > > +
> > > +                     if (is_llc != is_numa)
> > > +                             return true;
> > > +
> > > +                     sd = sd->parent;
> > > +             }
> > > +     }
> > > +
> > > +     return false;
> > > +}

Actually the logic here is not correct at all, because it's inspecting
also the sd of SMT CPUs for example, so it will end up enabling NUMA
when it's not needed. I'll rethink this part.

-Andrea