sched/fair: Clean up asym packing
Clean up asym packing to follow the default load balance behavior: - classify the group by creating a group_asym_packing field. - calculate the imbalance in calculate_imbalance() instead of bypassing it. We don't need to test twice same conditions anymore to detect asym packing and we consolidate the calculation of imbalance in calculate_imbalance(). There is no functional changes. Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> Acked-by: Rik van Riel <riel@surriel.com> Cc: Ben Segall <bsegall@google.com> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Mike Galbraith <efault@gmx.de> Cc: Morten.Rasmussen@arm.com Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: hdanton@sina.com Cc: parth@linux.ibm.com Cc: pauld@redhat.com Cc: quentin.perret@arm.com Cc: srikar@linux.vnet.ibm.com Cc: valentin.schneider@arm.com Link: https://lkml.kernel.org/r/1571405198-27570-2-git-send-email-vincent.guittot@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -7665,6 +7665,7 @@ struct sg_lb_stats {
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unsigned int group_weight;
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enum group_type group_type;
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int group_no_capacity;
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unsigned int group_asym_packing; /* Tasks should be moved to preferred CPU */
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unsigned long group_misfit_task_load; /* A CPU has a task too big for its capacity */
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#ifdef CONFIG_NUMA_BALANCING
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unsigned int nr_numa_running;
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@ -8119,9 +8120,17 @@ asym_packing:
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* ASYM_PACKING needs to move all the work to the highest
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* prority CPUs in the group, therefore mark all groups
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* of lower priority than ourself as busy.
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*
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* This is primarily intended to used at the sibling level. Some
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* cores like POWER7 prefer to use lower numbered SMT threads. In the
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* case of POWER7, it can move to lower SMT modes only when higher
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* threads are idle. When in lower SMT modes, the threads will
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* perform better since they share less core resources. Hence when we
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* have idle threads, we want them to be the higher ones.
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*/
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if (sgs->sum_nr_running &&
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sched_asym_prefer(env->dst_cpu, sg->asym_prefer_cpu)) {
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sgs->group_asym_packing = 1;
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if (!sds->busiest)
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return true;
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@ -8262,51 +8271,6 @@ next_group:
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}
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}
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/**
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* check_asym_packing - Check to see if the group is packed into the
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* sched domain.
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*
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* This is primarily intended to used at the sibling level. Some
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* cores like POWER7 prefer to use lower numbered SMT threads. In the
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* case of POWER7, it can move to lower SMT modes only when higher
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* threads are idle. When in lower SMT modes, the threads will
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* perform better since they share less core resources. Hence when we
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* have idle threads, we want them to be the higher ones.
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*
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* This packing function is run on idle threads. It checks to see if
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* the busiest CPU in this domain (core in the P7 case) has a higher
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* CPU number than the packing function is being run on. Here we are
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* assuming lower CPU number will be equivalent to lower a SMT thread
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* number.
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*
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* Return: 1 when packing is required and a task should be moved to
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* this CPU. The amount of the imbalance is returned in env->imbalance.
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*
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* @env: The load balancing environment.
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* @sds: Statistics of the sched_domain which is to be packed
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*/
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static int check_asym_packing(struct lb_env *env, struct sd_lb_stats *sds)
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{
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int busiest_cpu;
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if (!(env->sd->flags & SD_ASYM_PACKING))
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return 0;
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if (env->idle == CPU_NOT_IDLE)
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return 0;
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if (!sds->busiest)
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return 0;
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busiest_cpu = sds->busiest->asym_prefer_cpu;
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if (sched_asym_prefer(busiest_cpu, env->dst_cpu))
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return 0;
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env->imbalance = sds->busiest_stat.group_load;
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return 1;
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}
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/**
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* fix_small_imbalance - Calculate the minor imbalance that exists
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* amongst the groups of a sched_domain, during
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@ -8391,6 +8355,11 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
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local = &sds->local_stat;
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busiest = &sds->busiest_stat;
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if (busiest->group_asym_packing) {
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env->imbalance = busiest->group_load;
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return;
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}
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if (busiest->group_type == group_imbalanced) {
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/*
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* In the group_imb case we cannot rely on group-wide averages
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@ -8495,8 +8464,8 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
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busiest = &sds.busiest_stat;
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/* ASYM feature bypasses nice load balance check */
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if (check_asym_packing(env, &sds))
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return sds.busiest;
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if (busiest->group_asym_packing)
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goto force_balance;
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/* There is no busy sibling group to pull tasks from */
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if (!sds.busiest || busiest->sum_nr_running == 0)
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