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

["Chen, Yu C" <yu.c.chen@intel.com>]

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