Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 8 Jul 2022 09:17:30 +0200 | Subject | Re: [PATCH] sched/fair: fix case with reduced capacity CPU |
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On Thu, 7 Jul 2022 at 18:43, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: > > On 02/07/2022 06:52, Vincent Guittot wrote: > > 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 ? > > > > 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; > > I'm wondering why you've chosen that hybrid approach `group_misfit_task > -> migrate_load` and not `group_misfit_task -> migrate_misfit`.
because, it means enabling the tracking of misfit task on rq at each task enqueue/dequeue/tick ... Then mistfit for heterogeneous platform checks max_cpu_capacity what we don't care and will trigger unwanted misfit migration for smp
> > It looks like this `rq->cfs.h_nr_running = 1` case almost (since we > check `busiest->nr_running > 1`) always ends up in the load_balance() > `if (!ld_moved)` condition and need_active_balance() can return 1 in > case `if ((env->idle != CPU_NOT_IDLE) && ...` condition. This leads to > active load_balance and this > > IMHO, the same you can achieve when you would stay with > `group_misfit_task -> migrate_misfit`. > > I think cpu_load(rq) can be used instead of `rq->misfit_task_load` in > the migrate_misfit case of find_busiest_queue() too.
I don't think because you can have a higher cpu_load() but not being misfit
> > [...]
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