Messages in this thread | | | From | Vincent Guittot <> | Date | Sat, 18 Sep 2021 11:33:37 +0200 | Subject | Re: [PATCH v5 6/6] sched/fair: Consider SMT in ASYM_PACKING load balance |
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On Fri, 17 Sept 2021 at 20:47, Peter Zijlstra <peterz@infradead.org> wrote: > > On Fri, Sep 17, 2021 at 05:25:02PM +0200, Vincent Guittot wrote: > > > With the removal of the condition !sds->local_stat.sum_nr_running > > which seems useless because dst_cpu is idle and not SMT, this patch > > looks good to me > > I've made it look like this. Thanks!
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Thanks
> > --- > Subject: sched/fair: Consider SMT in ASYM_PACKING load balance > From: Ricardo Neri <ricardo.neri-calderon@linux.intel.com> > Date: Fri, 10 Sep 2021 18:18:19 -0700 > > From: Ricardo Neri <ricardo.neri-calderon@linux.intel.com> > > 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@linux.intel.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> > Reviewed-by: Len Brown <len.brown@intel.com> > Link: https://lkml.kernel.org/r/20210911011819.12184-7-ricardo.neri-calderon@linux.intel.com > --- > kernel/sched/fair.c | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 92 insertions(+) > > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -8538,10 +8538,96 @@ group_type group_classify(unsigned int i > 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); > } > > @@ -9547,6 +9633,12 @@ static struct rq *find_busiest_queue(str > 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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