Re: [PATCH v2 06/23] sched/cache: Track LLC-preferred tasks per runqueue

[Chen, Yu C]

On 12/17/2025 6:04 PM, Vern Hao wrote:
> On 2025/12/4 07:07, Tim Chen wrote:
> > @@ -1346,8 +1385,13 @@ void account_mm_sched(struct rq *rq, struct 
> > task_struct *p, s64 delta_exec)
> >   #endif
> >       }
> > -    if (p->preferred_llc != mm_sched_llc)
> > +    /* task not on rq accounted later in account_entity_enqueue() */
> > +    if (task_running_on_cpu(rq->cpu, p) &&
> > +        p->preferred_llc != mm_sched_llc) {
> > #ifdef CONFIG_NUMA_BALANCING
> >                  /*
> >                   * Don't assign preferred LLC if it
> >                   * conflicts with NUMA balancing.
> >                   */
> >                  if (p->numa_preferred_nid >= 0 &&
> >                      cpu_to_node(mm->mm_sched_cpu) != p- 
> >  >numa_preferred_nid)
> >                          mm_sched_llc = -1;
> > #endif
> >          }
> >
> >          /* task not on rq accounted later in account_entity_enqueue() */
> >          if (task_running_on_cpu(rq->cpu, p) &&
> >              p->preferred_llc != mm_sched_llc) {
> >                  account_llc_dequeue(rq, p);
> >                  p->preferred_llc = mm_sched_llc;
> >                  account_llc_enqueue(rq, p);
> >
> >          }
> I am a little concerned that there might be cases where both |p- 
>  >preferred_llc| and |mm_sched_llc| are equal to -1 at this point.", Is 
> it necessary to add a check here?

Are you concerned about the mismatch between the percpu runqueue values
of nr_pref_llc_running, nr_pref_llc, and nr_llc_running? This should not
be an issue, because account_llc_dequeue() and account_llc_enqueue() are
always invoked together in account_mm_sched(). If p->preferred_llc = 
mm_sched_llc = -1,
account_llc_dequeue/enqueue() will not be invoked, so it is still paired.
Please let me know if I understand your comments correctly.

thanks,
Chenyu