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Commit afe06efd authored by Tim Chen's avatar Tim Chen Committed by Thomas Gleixner
Browse files

sched: Extend scheduler's asym packing 



We generalize the scheduler's asym packing to provide an ordering
of the cpu beyond just the cpu number.  This allows the use of the
ASYM_PACKING scheduler machinery to move loads to preferred CPU in a
sched domain. The preference is defined with the cpu priority
given by arch_asym_cpu_priority(cpu).

We also record the most preferred cpu in a sched group when
we build the cpu's capacity for fast lookup of preferred cpu
during load balancing.

Co-developed-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarTim Chen <tim.c.chen@linux.intel.com>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: linux-pm@vger.kernel.org
Cc: jolsa@redhat.com
Cc: rjw@rjwysocki.net
Cc: linux-acpi@vger.kernel.org
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: bp@suse.de
Link: http://lkml.kernel.org/r/0e73ae12737dfaafa46c07066cc7c5d3f1675e46.1479844244.git.tim.c.chen@linux.intel.com


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 2b4d5b25

include/linux/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -1077,6 +1077,8 @@ static inline int cpu_numa_flags(void) 
}

#endif



extern int arch_asym_cpu_priority(int cpu);



struct sched_domain_attr {

	int relax_domain_level;

};

kernel/sched/core.c

+15 −0
Original line number Diff line number Diff line
@@ -6303,7 +6303,22 @@ static void init_sched_groups_capacity(int cpu, struct sched_domain *sd) 
	WARN_ON(!sg);



	do {

		int cpu, max_cpu = -1;



		sg->group_weight = cpumask_weight(sched_group_cpus(sg));



		if (!(sd->flags & SD_ASYM_PACKING))

			goto next;



		for_each_cpu(cpu, sched_group_cpus(sg)) {

			if (max_cpu < 0)

				max_cpu = cpu;

			else if (sched_asym_prefer(cpu, max_cpu))

				max_cpu = cpu;

		}

		sg->asym_prefer_cpu = max_cpu;



next:

		sg = sg->next;

	} while (sg != sd->groups);

kernel/sched/fair.c

+36 −17
Original line number Diff line number Diff line
@@ -97,6 +97,16 @@ unsigned int normalized_sysctl_sched_wakeup_granularity = 1000000UL; 


const_debug unsigned int sysctl_sched_migration_cost	= 500000UL;



#ifdef CONFIG_SMP

/*

 * For asym packing, by default the lower numbered cpu has higher priority.

 */

int __weak arch_asym_cpu_priority(int cpu)

{

	return -cpu;

}

#endif



#ifdef CONFIG_CFS_BANDWIDTH

/*

 * Amount of runtime to allocate from global (tg) to local (per-cfs_rq) pool
@@ -7388,16 +7398,18 @@ static bool update_sd_pick_busiest(struct lb_env *env, 
	if (env->idle == CPU_NOT_IDLE)

		return true;

	/*

	 * ASYM_PACKING needs to move all the work to the lowest

	 * numbered CPUs in the group, therefore mark all groups

	 * higher than ourself as busy.

	 * ASYM_PACKING needs to move all the work to the highest

	 * prority CPUs in the group, therefore mark all groups

	 * of lower priority than ourself as busy.

	 */

	if (sgs->sum_nr_running && env->dst_cpu < group_first_cpu(sg)) {

	if (sgs->sum_nr_running &&

	    sched_asym_prefer(env->dst_cpu, sg->asym_prefer_cpu)) {

		if (!sds->busiest)

			return true;



		/* Prefer to move from highest possible cpu's work */

		if (group_first_cpu(sds->busiest) < group_first_cpu(sg))

		/* Prefer to move from lowest priority cpu's work */

		if (sched_asym_prefer(sds->busiest->asym_prefer_cpu,

				      sg->asym_prefer_cpu))

			return true;

	}
@@ -7549,8 +7561,8 @@ static int check_asym_packing(struct lb_env *env, struct sd_lb_stats *sds) 
	if (!sds->busiest)

		return 0;



	busiest_cpu = group_first_cpu(sds->busiest);

	if (env->dst_cpu > busiest_cpu)

	busiest_cpu = sds->busiest->asym_prefer_cpu;

	if (sched_asym_prefer(busiest_cpu, env->dst_cpu))

		return 0;



	env->imbalance = DIV_ROUND_CLOSEST(
@@ -7888,10 +7900,11 @@ static int need_active_balance(struct lb_env *env) 


		/*

		 * ASYM_PACKING needs to force migrate tasks from busy but

		 * higher numbered CPUs in order to pack all tasks in the

		 * lowest numbered CPUs.

		 * lower priority CPUs in order to pack all tasks in the

		 * highest priority CPUs.

		 */

		if ((sd->flags & SD_ASYM_PACKING) && env->src_cpu > env->dst_cpu)

		if ((sd->flags & SD_ASYM_PACKING) &&

		    sched_asym_prefer(env->dst_cpu, env->src_cpu))

			return 1;

	}
@@ -8740,7 +8753,7 @@ static inline bool nohz_kick_needed(struct rq *rq) 
	unsigned long now = jiffies;

	struct sched_domain_shared *sds;

	struct sched_domain *sd;

	int nr_busy, cpu = rq->cpu;

	int nr_busy, i, cpu = rq->cpu;

	bool kick = false;



	if (unlikely(rq->idle_balance))
@@ -8791,12 +8804,18 @@ static inline bool nohz_kick_needed(struct rq *rq) 
	}



	sd = rcu_dereference(per_cpu(sd_asym, cpu));

	if (sd && (cpumask_first_and(nohz.idle_cpus_mask,

				  sched_domain_span(sd)) < cpu)) {

	if (sd) {

		for_each_cpu(i, sched_domain_span(sd)) {

			if (i == cpu ||

			    !cpumask_test_cpu(i, nohz.idle_cpus_mask))

				continue;



			if (sched_asym_prefer(i, cpu)) {

				kick = true;

				goto unlock;

			}



		}

	}

unlock:

	rcu_read_unlock();

	return kick;

kernel/sched/sched.h

+6 −0
Original line number Diff line number Diff line
@@ -540,6 +540,11 @@ struct dl_rq { 


#ifdef CONFIG_SMP



static inline bool sched_asym_prefer(int a, int b)

{

	return arch_asym_cpu_priority(a) > arch_asym_cpu_priority(b);

}



/*

 * We add the notion of a root-domain which will be used to define per-domain

 * variables. Each exclusive cpuset essentially defines an island domain by
@@ -908,6 +913,7 @@ struct sched_group { 


	unsigned int group_weight;

	struct sched_group_capacity *sgc;

	int asym_prefer_cpu;		/* cpu of highest priority in group */



	/*

	 * The CPUs this group covers.