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SubjectRe: [PATCH] sched/fair: fix case with reduced capacity CPU
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在 2022/7/2 12:52, Vincent Guittot 写道:
> The capacity of the CPU available for CFS tasks can be reduced because of
> other activities running on the latter. In such case, it's worth trying to
> move CFS tasks on a CPU with more available capacity.
>
> The rework of the load balance has filterd the case when the CPU is
> classified to be fully busy but its capacity is reduced.
>
> Check if CPU's capacity is reduced while gathering load balance statistics
> and classify it group_misfit_task instead of group_fully_busy so we can
> try to move the load on another CPU.
>
> Reported-by: David Chen <david.chen@nutanix.com>
> Reported-by: Zhang Qiao <zhangqiao22@huawei.com>
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
>
> David, Zhang,
>
> I haven't put your tested-by because I have reworked and cleaned the patch to
> cover more cases.
>
> Could you run some tests with this version ?

I tested with this version, it is ok.

Tested-by: Zhang Qiao <zhangqiao22@huawei.com>

Thanks

>
> Thanks
>
> kernel/sched/fair.c | 50 ++++++++++++++++++++++++++++++++++++---------
> 1 file changed, 40 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index a78d2e3b9d49..126b82ef4279 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8798,6 +8798,19 @@ sched_asym(struct lb_env *env, struct sd_lb_stats *sds, struct sg_lb_stats *sgs
> return sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu);
> }
>
> +static inline bool
> +sched_reduced_capacity(struct rq *rq, struct sched_domain *sd)
> +{
> + /*
> + * When there is more than 1 task, the group_overloaded case already
> + * takes care of cpu with reduced capacity
> + */
> + if (rq->cfs.h_nr_running != 1)
> + return false;
> +
> + return check_cpu_capacity(rq, sd);
> +}
> +
> /**
> * update_sg_lb_stats - Update sched_group's statistics for load balancing.
> * @env: The load balancing environment.
> @@ -8820,8 +8833,9 @@ static inline void update_sg_lb_stats(struct lb_env *env,
>
> for_each_cpu_and(i, sched_group_span(group), env->cpus) {
> struct rq *rq = cpu_rq(i);
> + unsigned long load = cpu_load(rq);
>
> - sgs->group_load += cpu_load(rq);
> + sgs->group_load += load;
> sgs->group_util += cpu_util_cfs(i);
> sgs->group_runnable += cpu_runnable(rq);
> sgs->sum_h_nr_running += rq->cfs.h_nr_running;
> @@ -8851,11 +8865,17 @@ static inline void update_sg_lb_stats(struct lb_env *env,
> if (local_group)
> continue;
>
> - /* Check for a misfit task on the cpu */
> - if (env->sd->flags & SD_ASYM_CPUCAPACITY &&
> - sgs->group_misfit_task_load < rq->misfit_task_load) {
> - sgs->group_misfit_task_load = rq->misfit_task_load;
> - *sg_status |= SG_OVERLOAD;
> + if (env->sd->flags & SD_ASYM_CPUCAPACITY) {
> + /* Check for a misfit task on the cpu */
> + if (sgs->group_misfit_task_load < rq->misfit_task_load) {
> + sgs->group_misfit_task_load = rq->misfit_task_load;
> + *sg_status |= SG_OVERLOAD;
> + }
> + } else if ((env->idle != CPU_NOT_IDLE) &&
> + sched_reduced_capacity(rq, env->sd) &&
> + (sgs->group_misfit_task_load < load)) {
> + /* Check for a task running on a CPU with reduced capacity */
> + sgs->group_misfit_task_load = load;
> }
> }
>
> @@ -8908,7 +8928,8 @@ static bool update_sd_pick_busiest(struct lb_env *env,
> * CPUs in the group should either be possible to resolve
> * internally or be covered by avg_load imbalance (eventually).
> */
> - if (sgs->group_type == group_misfit_task &&
> + if ((env->sd->flags & SD_ASYM_CPUCAPACITY) &&
> + (sgs->group_type == group_misfit_task) &&
> (!capacity_greater(capacity_of(env->dst_cpu), sg->sgc->max_capacity) ||
> sds->local_stat.group_type != group_has_spare))
> return false;
> @@ -9517,9 +9538,18 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
> busiest = &sds->busiest_stat;
>
> if (busiest->group_type == group_misfit_task) {
> - /* Set imbalance to allow misfit tasks to be balanced. */
> - env->migration_type = migrate_misfit;
> - env->imbalance = 1;
> + if (env->sd->flags & SD_ASYM_CPUCAPACITY) {
> + /* Set imbalance to allow misfit tasks to be balanced. */
> + env->migration_type = migrate_misfit;
> + env->imbalance = 1;
> + } else {
> + /*
> + * Set load imbalance to allow moving task from cpu
> + * with reduced capacity
> + */
> + env->migration_type = migrate_load;
> + env->imbalance = busiest->group_misfit_task_load;
> + }
> return;
> }
>
>

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