Messages in this thread Patch in this message | | | From | Valentin Schneider <> | Subject | [PATCH v3 3/7] sched/fair: Add more sched_asym_cpucapacity static branch checks | Date | Thu, 11 Mar 2021 12:05:23 +0000 |
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Rik noted a while back that a handful of
sd->flags & SD_ASYM_CPUCAPACITY
& family in the CFS load-balancer code aren't guarded by the sched_asym_cpucapacity static branch.
Turning those checks into NOPs for those who don't need it is fairly straightforward, and hiding it in a helper doesn't change code size in all but one spot. It also gives us a place to document the differences between checking the static key and checking the SD flag.
Suggested-by: Rik van Riel <riel@surriel.com> Reviewed-by: Qais Yousef <qais.yousef@arm.com> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com> --- kernel/sched/fair.c | 21 ++++++++------------- kernel/sched/sched.h | 33 +++++++++++++++++++++++++++++++++ 2 files changed, 41 insertions(+), 13 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index f50a902bdf24..db892f6e222f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6300,15 +6300,8 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) * sd_asym_cpucapacity rather than sd_llc. */ if (static_branch_unlikely(&sched_asym_cpucapacity)) { + /* See sd_has_asym_cpucapacity() */ sd = rcu_dereference(per_cpu(sd_asym_cpucapacity, target)); - /* - * On an asymmetric CPU capacity system where an exclusive - * cpuset defines a symmetric island (i.e. one unique - * capacity_orig value through the cpuset), the key will be set - * but the CPUs within that cpuset will not have a domain with - * SD_ASYM_CPUCAPACITY. These should follow the usual symmetric - * capacity path. - */ if (sd) { i = select_idle_capacity(p, sd, target); return ((unsigned)i < nr_cpumask_bits) ? i : target; @@ -8467,7 +8460,7 @@ static inline void update_sg_lb_stats(struct lb_env *env, continue; /* Check for a misfit task on the cpu */ - if (env->sd->flags & SD_ASYM_CPUCAPACITY && + if (sd_has_asym_cpucapacity(env->sd) && sgs->group_misfit_task_load < rq->misfit_task_load) { sgs->group_misfit_task_load = rq->misfit_task_load; *sg_status |= SG_OVERLOAD; @@ -8524,7 +8517,8 @@ 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 (static_branch_unlikely(&sched_asym_cpucapacity) && + sgs->group_type == group_misfit_task && (!group_smaller_max_cpu_capacity(sg, sds->local) || sds->local_stat.group_type != group_has_spare)) return false; @@ -8607,7 +8601,7 @@ static bool update_sd_pick_busiest(struct lb_env *env, * throughput. Maximize throughput, power/energy consequences are not * considered. */ - if ((env->sd->flags & SD_ASYM_CPUCAPACITY) && + if (sd_has_asym_cpucapacity(env->sd) && (sgs->group_type <= group_fully_busy) && (group_smaller_min_cpu_capacity(sds->local, sg))) return false; @@ -8730,7 +8724,7 @@ static inline void update_sg_wakeup_stats(struct sched_domain *sd, } /* Check if task fits in the group */ - if (sd->flags & SD_ASYM_CPUCAPACITY && + if (sd_has_asym_cpucapacity(sd) && !task_fits_capacity(p, group->sgc->max_capacity)) { sgs->group_misfit_task_load = 1; } @@ -9408,7 +9402,7 @@ static struct rq *find_busiest_queue(struct lb_env *env, * Higher per-CPU capacity is considered better than balancing * average load. */ - if (env->sd->flags & SD_ASYM_CPUCAPACITY && + if (sd_has_asym_cpucapacity(env->sd) && capacity_of(env->dst_cpu) < capacity && nr_running == 1) continue; @@ -10225,6 +10219,7 @@ static void nohz_balancer_kick(struct rq *rq) } } + /* See sd_has_asym_cpucapacity(). */ sd = rcu_dereference(per_cpu(sd_asym_cpucapacity, cpu)); if (sd) { /* diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index d2e09a647c4f..27bf70bc86c7 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1492,6 +1492,39 @@ DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing); DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity); extern struct static_key_false sched_asym_cpucapacity; +/* + * Note that the static key is system-wide, but the visibility of + * SD_ASYM_CPUCAPACITY isn't. Thus the static key being enabled does not + * imply all CPUs can see asymmetry. + * + * Consider an asymmetric CPU capacity system such as: + * + * MC [ ] + * 0 1 2 3 4 5 + * L L L L B B + * + * w/ arch_scale_cpu_capacity(L) < arch_scale_cpu_capacity(B) + * + * By default, booting this system will enable the sched_asym_cpucapacity + * static key, and all CPUs will see SD_ASYM_CPUCAPACITY set at their MC + * sched_domain. + * + * Further consider exclusive cpusets creating a "symmetric island": + * + * MC [ ][ ] + * 0 1 2 3 4 5 + * L L L L B B + * + * Again, booting this will enable the static key, but CPUs 0-1 will *not* have + * SD_ASYM_CPUCAPACITY set in any of their sched_domain. This is the intended + * behaviour, as CPUs 0-1 should be treated as a regular, isolated SMP system. + */ +static inline bool sd_has_asym_cpucapacity(struct sched_domain *sd) +{ + return static_branch_unlikely(&sched_asym_cpucapacity) && + sd->flags & SD_ASYM_CPUCAPACITY; +} + struct sched_group_capacity { atomic_t ref; /* -- 2.25.1
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