The following commit has been merged into the sched/core branch of tip: Commit-ID: 4006a72bdd93b1ffedc2bd8646dee18c822a2c26 Gitweb: https://git.kernel.org/tip/4006a72bdd93b1ffedc2bd8646dee18c822a2c26 Author: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx> AuthorDate: Fri, 10 Sep 2021 18:18:19 -07:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Tue, 05 Oct 2021 15:52:06 +02:00 sched/fair: Consider SMT in ASYM_PACKING load balance When deciding to pull tasks in ASYM_PACKING, it is necessary not only to check for the idle state of the destination CPU, dst_cpu, but also of its SMT siblings. If dst_cpu is idle but its SMT siblings are busy, performance suffers if it pulls tasks from a medium priority CPU that does not have SMT siblings. Implement asym_smt_can_pull_tasks() to inspect the state of the SMT siblings of both dst_cpu and the CPUs in the candidate busiest group. Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> Reviewed-by: Len Brown <len.brown@xxxxxxxxx> Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx> Link: https://lkml.kernel.org/r/20210911011819.12184-7-ricardo.neri-calderon@xxxxxxxxxxxxxxx --- kernel/sched/fair.c | 92 ++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 92 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 1c8b5fa..c50ae23 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -8571,10 +8571,96 @@ group_type group_classify(unsigned int imbalance_pct, return group_has_spare; } +/** + * asym_smt_can_pull_tasks - Check whether the load balancing CPU can pull tasks + * @dst_cpu: Destination CPU of the load balancing + * @sds: Load-balancing data with statistics of the local group + * @sgs: Load-balancing statistics of the candidate busiest group + * @sg: The candidate busiest group + * + * Check the state of the SMT siblings of both @sds::local and @sg and decide + * if @dst_cpu can pull tasks. + * + * If @dst_cpu does not have SMT siblings, it can pull tasks if two or more of + * the SMT siblings of @sg are busy. If only one CPU in @sg is busy, pull tasks + * only if @dst_cpu has higher priority. + * + * If both @dst_cpu and @sg have SMT siblings, and @sg has exactly one more + * busy CPU than @sds::local, let @dst_cpu pull tasks if it has higher priority. + * Bigger imbalances in the number of busy CPUs will be dealt with in + * update_sd_pick_busiest(). + * + * If @sg does not have SMT siblings, only pull tasks if all of the SMT siblings + * of @dst_cpu are idle and @sg has lower priority. + */ +static bool asym_smt_can_pull_tasks(int dst_cpu, struct sd_lb_stats *sds, + struct sg_lb_stats *sgs, + struct sched_group *sg) +{ +#ifdef CONFIG_SCHED_SMT + bool local_is_smt, sg_is_smt; + int sg_busy_cpus; + + local_is_smt = sds->local->flags & SD_SHARE_CPUCAPACITY; + sg_is_smt = sg->flags & SD_SHARE_CPUCAPACITY; + + sg_busy_cpus = sgs->group_weight - sgs->idle_cpus; + + if (!local_is_smt) { + /* + * If we are here, @dst_cpu is idle and does not have SMT + * siblings. Pull tasks if candidate group has two or more + * busy CPUs. + */ + if (sg_busy_cpus >= 2) /* implies sg_is_smt */ + return true; + + /* + * @dst_cpu does not have SMT siblings. @sg may have SMT + * siblings and only one is busy. In such case, @dst_cpu + * can help if it has higher priority and is idle (i.e., + * it has no running tasks). + */ + return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu); + } + + /* @dst_cpu has SMT siblings. */ + + if (sg_is_smt) { + int local_busy_cpus = sds->local->group_weight - + sds->local_stat.idle_cpus; + int busy_cpus_delta = sg_busy_cpus - local_busy_cpus; + + if (busy_cpus_delta == 1) + return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu); + + return false; + } + + /* + * @sg does not have SMT siblings. Ensure that @sds::local does not end + * up with more than one busy SMT sibling and only pull tasks if there + * are not busy CPUs (i.e., no CPU has running tasks). + */ + if (!sds->local_stat.sum_nr_running) + return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu); + + return false; +#else + /* Always return false so that callers deal with non-SMT cases. */ + return false; +#endif +} + static inline bool sched_asym(struct lb_env *env, struct sd_lb_stats *sds, struct sg_lb_stats *sgs, struct sched_group *group) { + /* Only do SMT checks if either local or candidate have SMT siblings */ + if ((sds->local->flags & SD_SHARE_CPUCAPACITY) || + (group->flags & SD_SHARE_CPUCAPACITY)) + return asym_smt_can_pull_tasks(env->dst_cpu, sds, sgs, group); + return sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu); } @@ -9580,6 +9666,12 @@ static struct rq *find_busiest_queue(struct lb_env *env, nr_running == 1) continue; + /* Make sure we only pull tasks from a CPU of lower priority */ + if ((env->sd->flags & SD_ASYM_PACKING) && + sched_asym_prefer(i, env->dst_cpu) && + nr_running == 1) + continue; + switch (env->migration_type) { case migrate_load: /*
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