Re: [PATCH v5 3/5] sched/fair: Rework sched_use_asym_prio() and sched_asym_prefer()

[kuiliang Shi]

On 2/14/24 12:51 AM, Vincent Guittot wrote:
> On Sat, 10 Feb 2024 at 12:36, <alexs@xxxxxxxxxx> wrote:
>>
>> From: Alex Shi <alexs@xxxxxxxxxx>
>>
>> sched_use_asym_prio() and sched_asym_prefer() are used together in various
>> places. Consolidate them into a single function sched_asym().
>>
>> The existing sched_group_asym() is only used when collecting statistics
> 
> nit: The existing sched_asym()

Hi Vincent,

Thanks for all reviewing. Do I need to update this for next version? or just fix it during merge?

Alex

> 
>> of a scheduling group. Rename it as sched_group_asym(), and remove the
>> obsolete function description.
>>
>> This makes the code easier to read. No functional changes.
>>
>> Tested-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
>> Signed-off-by: Alex Shi <alexs@xxxxxxxxxx>
>> Cc: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
>> Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
>> Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
>> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
>> Reviewed-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
> 
> Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> 
>> ---
>>  kernel/sched/fair.c | 45 ++++++++++++++++++++-------------------------
>>  1 file changed, 20 insertions(+), 25 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 607dc310b355..426eda9eda57 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -9746,8 +9746,18 @@ static bool sched_use_asym_prio(struct sched_domain *sd, int cpu)
>>         return sd->flags & SD_SHARE_CPUCAPACITY || is_core_idle(cpu);
>>  }
>>
>> +static inline bool sched_asym(struct sched_domain *sd, int dst_cpu, int src_cpu)
>> +{
>> +       /*
>> +        * First check if @dst_cpu can do asym_packing load balance. Only do it
>> +        * if it has higher priority than @src_cpu.
>> +        */
>> +       return sched_use_asym_prio(sd, dst_cpu) &&
>> +               sched_asym_prefer(dst_cpu, src_cpu);
>> +}
>> +
>>  /**
>> - * sched_asym - Check if the destination CPU can do asym_packing load balance
>> + * sched_group_asym - Check if the destination CPU can do asym_packing balance
>>   * @env:       The load balancing environment
>>   * @sgs:       Load-balancing statistics of the candidate busiest group
>>   * @group:     The candidate busiest group
>> @@ -9755,34 +9765,21 @@ static bool sched_use_asym_prio(struct sched_domain *sd, int cpu)
>>   * @env::dst_cpu can do asym_packing if it has higher priority than the
>>   * preferred CPU of @group.
>>   *
>> - * SMT is a special case. If we are balancing load between cores, @env::dst_cpu
>> - * can do asym_packing balance only if all its SMT siblings are idle. Also, it
>> - * can only do it if @group is an SMT group and has exactly on busy CPU. Larger
>> - * imbalances in the number of CPUS are dealt with in find_busiest_group().
>> - *
>> - * If we are balancing load within an SMT core, or at PKG domain level, always
>> - * proceed.
>> - *
>>   * Return: true if @env::dst_cpu can do with asym_packing load balance. False
>>   * otherwise.
>>   */
>>  static inline bool
>> -sched_asym(struct lb_env *env, struct sg_lb_stats *sgs, struct sched_group *group)
>> +sched_group_asym(struct lb_env *env, struct sg_lb_stats *sgs, struct sched_group *group)
>>  {
>> -       /* Ensure that the whole local core is idle, if applicable. */
>> -       if (!sched_use_asym_prio(env->sd, env->dst_cpu))
>> -               return false;
>> -
>>         /*
>> -        * CPU priorities does not make sense for SMT cores with more than one
>> +        * CPU priorities do not make sense for SMT cores with more than one
>>          * busy sibling.
>>          */
>> -       if (group->flags & SD_SHARE_CPUCAPACITY) {
>> -               if (sgs->group_weight - sgs->idle_cpus != 1)
>> -                       return false;
>> -       }
>> +       if ((group->flags & SD_SHARE_CPUCAPACITY) &&
>> +           (sgs->group_weight - sgs->idle_cpus != 1))
>> +               return false;
>>
>> -       return sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu);
>> +       return sched_asym(env->sd, env->dst_cpu, group->asym_prefer_cpu);
>>  }
>>
>>  /* One group has more than one SMT CPU while the other group does not */
>> @@ -9938,7 +9935,7 @@ static inline void update_sg_lb_stats(struct lb_env *env,
>>         /* Check if dst CPU is idle and preferred to this group */
>>         if (!local_group && env->sd->flags & SD_ASYM_PACKING &&
>>             env->idle != CPU_NOT_IDLE && sgs->sum_h_nr_running &&
>> -           sched_asym(env, sgs, group)) {
>> +           sched_group_asym(env, sgs, group)) {
>>                 sgs->group_asym_packing = 1;
>>         }
>>
>> @@ -11037,8 +11034,7 @@ static struct rq *find_busiest_queue(struct lb_env *env,
>>                  * SMT cores with more than one busy sibling.
>>                  */
>>                 if ((env->sd->flags & SD_ASYM_PACKING) &&
>> -                   sched_use_asym_prio(env->sd, i) &&
>> -                   sched_asym_prefer(i, env->dst_cpu) &&
>> +                   sched_asym(env->sd, i, env->dst_cpu) &&
>>                     nr_running == 1)
>>                         continue;
>>
>> @@ -11908,8 +11904,7 @@ static void nohz_balancer_kick(struct rq *rq)
>>                  * preferred CPU must be idle.
>>                  */
>>                 for_each_cpu_and(i, sched_domain_span(sd), nohz.idle_cpus_mask) {
>> -                       if (sched_use_asym_prio(sd, i) &&
>> -                           sched_asym_prefer(i, cpu)) {
>> +                       if (sched_asym(sd, i, cpu)) {
>>                                 flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK;
>>                                 goto unlock;
>>                         }
>> --
>> 2.43.0
>>