Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1429003

[PATCH v2 11/13] sched/fair: Avoid pulling tasks from non-overloaded higher capacity groups

Show all headers | View raw

For asymmetric cpu capacity systems it is counter-productive for
throughput if low capacity cpus are pulling tasks from non-overloaded
cpus with higher capacity. The assumption is that higher cpu capacity is
preferred over running alone in a group with lower cpu capacity.

This patch rejects higher cpu capacity groups with one or less task per
cpu as potential busiest group which could otherwise lead to a series of
failing load-balancing attempts leading to a force-migration.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>

Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
---
 kernel/sched/fair.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4d10d022006d..ca0048d95b3f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6789,6 +6789,17 @@ group_is_overloaded(struct lb_env *env, struct sg_lb_stats *sgs)
 	return false;
 }
 
+/*
+ * group_smaller_cpu_capacity: Returns true if sched_group sg has smaller
+ * per-cpu capacity than sched_group ref.
+ */
+static inline bool
+group_smaller_cpu_capacity(struct sched_group *sg, struct sched_group *ref)
+{
+	return sg->sgc->max_capacity * capacity_margin <
+						ref->sgc->max_capacity * 1024;
+}
+
 static inline enum
 group_type group_classify(struct sched_group *group,
 			  struct sg_lb_stats *sgs)
@@ -6892,6 +6903,19 @@ static bool update_sd_pick_busiest(struct lb_env *env,
 	if (sgs->avg_load <= busiest->avg_load)
 		return false;
 
+	if (!(env->sd->flags & SD_ASYM_CPUCAPACITY))
+		goto asym_packing;
+
+	/* Candidate sg has no more than one task per cpu and has
+	 * higher per-cpu capacity. Migrating tasks to less capable
+	 * cpus may harm throughput. Maximize throughput,
+	 * power/energy consequences are not considered.
+	 */
+	if (sgs->sum_nr_running <= sgs->group_weight &&
+	    group_smaller_cpu_capacity(sds->local, sg))
+		return false;
+
+asym_packing:
 	/* This is the busiest node in its class. */
 	if (!(env->sd->flags & SD_ASYM_PACKING))
 		return true;
-- 
1.9.1

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH v2 00/13] sched: Clean-ups and asymmetric cpu capacity support Morten Rasmussen <morten.rasmussen@arm.com> - 2016-06-22 19:10 +0200
  [PATCH v2 11/13] sched/fair: Avoid pulling tasks from non-overloaded higher capacity groups Morten Rasmussen <morten.rasmussen@arm.com> - 2016-06-22 19:10 +0200
  [PATCH v2 09/13] sched/fair: Consider spare capacity in find_idlest_group() Morten Rasmussen <morten.rasmussen@arm.com> - 2016-06-22 19:10 +0200
  [PATCH v2 12/13] arm: Set SD_ASYM_CPUCAPACITY for big.LITTLE platforms Morten Rasmussen <morten.rasmussen@arm.com> - 2016-06-22 19:10 +0200
  [PATCH v2 05/13] sched: Enable SD_BALANCE_WAKE for asymmetric capacity systems Morten Rasmussen <morten.rasmussen@arm.com> - 2016-06-22 19:10 +0200

csiph-web