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Fri, 19 Jul 2019 07:13:48 -0700 (PDT) MIME-Version: 1.0 References: <1563523105-24673-1-git-send-email-vincent.guittot@linaro.org> <1563523105-24673-4-git-send-email-vincent.guittot@linaro.org> <20190719131255.GL3419@hirez.programming.kicks-ass.net> In-Reply-To: <20190719131255.GL3419@hirez.programming.kicks-ass.net> From: Vincent Guittot Date: Fri, 19 Jul 2019 16:13:38 +0200 Message-ID: Subject: Re: [PATCH 3/5] sched/fair: rework load_balance To: Peter Zijlstra Cc: linux-kernel , Ingo Molnar , Quentin Perret , Dietmar Eggemann , Morten Rasmussen , Phil Auld Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 19 Jul 2019 at 15:12, Peter Zijlstra wrote: > > On Fri, Jul 19, 2019 at 09:58:23AM +0200, Vincent Guittot wrote: > > > @@ -8029,17 +8063,24 @@ static inline void update_sg_lb_stats(struct lb_env *env, > > } > > } > > > > - /* Adjust by relative CPU capacity of the group */ > > - sgs->group_capacity = group->sgc->capacity; > > - sgs->avg_load = (sgs->group_load*SCHED_CAPACITY_SCALE) / sgs->group_capacity; > > + /* Check if dst cpu is idle and preferred to this group */ > > + if (env->sd->flags & SD_ASYM_PACKING && > > + env->idle != CPU_NOT_IDLE && > > + sgs->sum_h_nr_running && > > + sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu)) { > > + sgs->group_asym_capacity = 1; > > + } > > > > - if (sgs->sum_h_nr_running) > > - sgs->load_per_task = sgs->group_load / sgs->sum_h_nr_running; > > + sgs->group_capacity = group->sgc->capacity; > > > > sgs->group_weight = group->group_weight; > > > > - sgs->group_no_capacity = group_is_overloaded(env, sgs); > > - sgs->group_type = group_classify(group, sgs); > > + sgs->group_type = group_classify(env, group, sgs); > > + > > + /* Computing avg_load makes sense only when group is overloaded */ > > + if (sgs->group_type != group_overloaded) > > The comment seems to suggest you meant: == yes looks like you're right :-( > > > + sgs->avg_load = (sgs->group_load*SCHED_CAPACITY_SCALE) / > > + sgs->group_capacity; > > } > > > > /** > > @@ -8070,7 +8111,7 @@ static bool update_sd_pick_busiest(struct lb_env *env, > > */ > > if (sgs->group_type == group_misfit_task && > > (!group_smaller_max_cpu_capacity(sg, sds->local) || > > - !group_has_capacity(env, &sds->local_stat))) > > + sds->local_stat.group_type != group_has_spare)) > > return false; > > > > if (sgs->group_type > busiest->group_type) > > @@ -8079,11 +8120,18 @@ static bool update_sd_pick_busiest(struct lb_env *env, > > if (sgs->group_type < busiest->group_type) > > return false; > > > > - if (sgs->avg_load <= busiest->avg_load) > > + /* Select the overloaded group with highest avg_load */ > > + if (sgs->group_type == group_overloaded && > > + sgs->avg_load <= busiest->avg_load) > > And this code does too; because with the above '!=', you're comparing > uninitialized data here, no? avg_load is always 0 and the load_balance was quite conservative when system was overloaded > > > + return false; > > + > > + /* Prefer to move from lowest priority CPU's work */ > > + if (sgs->group_type == group_asym_capacity && sds->busiest && > > + sched_asym_prefer(sg->asym_prefer_cpu, sds->busiest->asym_prefer_cpu)) > > return false; > > > > if (!(env->sd->flags & SD_ASYM_CPUCAPACITY)) > > - goto asym_packing; > > + goto spare_capacity; > > > > /* > > * Candidate sg has no more than one task per CPU and