Commit 490ba971 authored by Vincent Guittot's avatar Vincent Guittot Committed by Ingo Molnar
Browse files

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: default avatarVincent Guittot <vincent.guittot@linaro.org>
Acked-by: default avatarRik 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: default avatarIngo Molnar <mingo@kernel.org>
parent 9ae7ab20

kernel/sched/fair.c

+16 −47
Original line number Diff line number Diff line
@@ -7665,6 +7665,7 @@ struct sg_lb_stats { 
	unsigned int group_weight;

	enum group_type group_type;

	int group_no_capacity;

	unsigned int group_asym_packing; /* Tasks should be moved to preferred CPU */

	unsigned long group_misfit_task_load; /* A CPU has a task too big for its capacity */

#ifdef CONFIG_NUMA_BALANCING

	unsigned int nr_numa_running;
@@ -8119,9 +8120,17 @@ asym_packing: 
	 * 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.

	 *

	 * This is primarily intended to used at the sibling level.  Some

	 * cores like POWER7 prefer to use lower numbered SMT threads.  In the

	 * case of POWER7, it can move to lower SMT modes only when higher

	 * threads are idle.  When in lower SMT modes, the threads will

	 * perform better since they share less core resources.  Hence when we

	 * have idle threads, we want them to be the higher ones.

	 */

	if (sgs->sum_nr_running &&

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

		sgs->group_asym_packing = 1;

		if (!sds->busiest)

			return true;
@@ -8262,51 +8271,6 @@ next_group: 
	}

}



/**

 * check_asym_packing - Check to see if the group is packed into the

 *			sched domain.

 *

 * This is primarily intended to used at the sibling level.  Some

 * cores like POWER7 prefer to use lower numbered SMT threads.  In the

 * case of POWER7, it can move to lower SMT modes only when higher

 * threads are idle.  When in lower SMT modes, the threads will

 * perform better since they share less core resources.  Hence when we

 * have idle threads, we want them to be the higher ones.

 *

 * This packing function is run on idle threads.  It checks to see if

 * the busiest CPU in this domain (core in the P7 case) has a higher

 * CPU number than the packing function is being run on.  Here we are

 * assuming lower CPU number will be equivalent to lower a SMT thread

 * number.

 *

 * Return: 1 when packing is required and a task should be moved to

 * this CPU.  The amount of the imbalance is returned in env->imbalance.

 *

 * @env: The load balancing environment.

 * @sds: Statistics of the sched_domain which is to be packed

 */

static int check_asym_packing(struct lb_env *env, struct sd_lb_stats *sds)

{

	int busiest_cpu;



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

		return 0;



	if (env->idle == CPU_NOT_IDLE)

		return 0;



	if (!sds->busiest)

		return 0;



	busiest_cpu = sds->busiest->asym_prefer_cpu;

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

		return 0;



	env->imbalance = sds->busiest_stat.group_load;



	return 1;

}



/**

 * fix_small_imbalance - Calculate the minor imbalance that exists

 *			amongst the groups of a sched_domain, during
@@ -8391,6 +8355,11 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s 
	local = &sds->local_stat;

	busiest = &sds->busiest_stat;



	if (busiest->group_asym_packing) {

		env->imbalance = busiest->group_load;

		return;

	}



	if (busiest->group_type == group_imbalanced) {

		/*

		 * In the group_imb case we cannot rely on group-wide averages
@@ -8495,8 +8464,8 @@ static struct sched_group *find_busiest_group(struct lb_env *env) 
	busiest = &sds.busiest_stat;



	/* ASYM feature bypasses nice load balance check */

	if (check_asym_packing(env, &sds))

		return sds.busiest;

	if (busiest->group_asym_packing)

		goto force_balance;



	/* There is no busy sibling group to pull tasks from */

	if (!sds.busiest || busiest->sum_nr_running == 0)

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