Commit fc1273f4 authored by Vincent Guittot's avatar Vincent Guittot Committed by Ingo Molnar
Browse files

sched/fair: Optimize find_idlest_group() 



find_idlest_group() now reads CPU's load_avg in two different ways.

Consolidate the function to read and use load_avg only once and simplify
the algorithm to only look for the group with lowest load_avg.

Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
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: riel@surriel.com
Cc: srikar@linux.vnet.ibm.com
Cc: valentin.schneider@arm.com
Link: https://lkml.kernel.org/r/1571405198-27570-11-git-send-email-vincent.guittot@linaro.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 11f10e54

kernel/sched/fair.c

+14 −36
Original line number Diff line number Diff line
@@ -5550,16 +5550,14 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, 
{

	struct sched_group *idlest = NULL, *group = sd->groups;

	struct sched_group *most_spare_sg = NULL;

	unsigned long min_runnable_load = ULONG_MAX;

	unsigned long this_runnable_load = ULONG_MAX;

	unsigned long min_avg_load = ULONG_MAX, this_avg_load = ULONG_MAX;

	unsigned long min_load = ULONG_MAX, this_load = ULONG_MAX;

	unsigned long most_spare = 0, this_spare = 0;

	int imbalance_scale = 100 + (sd->imbalance_pct-100)/2;

	unsigned long imbalance = scale_load_down(NICE_0_LOAD) *

				(sd->imbalance_pct-100) / 100;



	do {

		unsigned long load, avg_load, runnable_load;

		unsigned long load;

		unsigned long spare_cap, max_spare_cap;

		int local_group;

		int i;
@@ -5576,15 +5574,11 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, 
		 * Tally up the load of all CPUs in the group and find

		 * the group containing the CPU with most spare capacity.

		 */

		avg_load = 0;

		runnable_load = 0;

		load = 0;

		max_spare_cap = 0;



		for_each_cpu(i, sched_group_span(group)) {

			load = cpu_load(cpu_rq(i));

			runnable_load += load;



			avg_load += cfs_rq_load_avg(&cpu_rq(i)->cfs);

			load += cpu_load(cpu_rq(i));



			spare_cap = capacity_spare_without(i, p);
@@ -5593,31 +5587,15 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, 
		}



		/* Adjust by relative CPU capacity of the group */

		avg_load = (avg_load * SCHED_CAPACITY_SCALE) /

					group->sgc->capacity;

		runnable_load = (runnable_load * SCHED_CAPACITY_SCALE) /

		load = (load * SCHED_CAPACITY_SCALE) /

					group->sgc->capacity;



		if (local_group) {

			this_runnable_load = runnable_load;

			this_avg_load = avg_load;

			this_load = load;

			this_spare = max_spare_cap;

		} else {

			if (min_runnable_load > (runnable_load + imbalance)) {

				/*

				 * The runnable load is significantly smaller

				 * so we can pick this new CPU:

				 */

				min_runnable_load = runnable_load;

				min_avg_load = avg_load;

				idlest = group;

			} else if ((runnable_load < (min_runnable_load + imbalance)) &&

				   (100*min_avg_load > imbalance_scale*avg_load)) {

				/*

				 * The runnable loads are close so take the

				 * blocked load into account through avg_load:

				 */

				min_avg_load = avg_load;

			if (load < min_load) {

				min_load = load;

				idlest = group;

			}
@@ -5658,18 +5636,18 @@ skip_spare: 
	 * local domain to be very lightly loaded relative to the remote

	 * domains but "imbalance" skews the comparison making remote CPUs

	 * look much more favourable. When considering cross-domain, add

	 * imbalance to the runnable load on the remote node and consider

	 * staying local.

	 * imbalance to the load on the remote node and consider staying

	 * local.

	 */

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

	    min_runnable_load + imbalance >= this_runnable_load)

	     min_load + imbalance >= this_load)

		return NULL;



	if (min_runnable_load > (this_runnable_load + imbalance))

	if (min_load >= this_load + imbalance)

		return NULL;



	if ((this_runnable_load < (min_runnable_load + imbalance)) &&

	     (100*this_avg_load < imbalance_scale*min_avg_load))

	if ((this_load < (min_load + imbalance)) &&

	    (100*this_load < imbalance_scale*min_load))

		return NULL;



	return idlest;

CRA Git | Maintained and supported by SUSTech CRA and CCSE