Commit 13ede331 authored by Mel Gorman's avatar Mel Gorman Committed by Peter Zijlstra
Browse files

sched/numa: Do not swap tasks between nodes when spare capacity is available 



If a destination node has spare capacity but there is an imbalance then
two tasks are selected for swapping. If the tasks have no numa group
or are within the same NUMA group, it's simply shuffling tasks around
without having any impact on the compute imbalance. Instead, it's just
punishing one task to help another.

Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: default avatarK Prateek Nayak <kprateek.nayak@amd.com>
Link: https://lore.kernel.org/r/20220520103519.1863-3-mgorman@techsingularity.net
parent 70ce3ea9

kernel/sched/fair.c

+9 −0
Original line number Diff line number Diff line
@@ -1790,6 +1790,15 @@ static bool task_numa_compare(struct task_numa_env *env, 
	 */

	cur_ng = rcu_dereference(cur->numa_group);

	if (cur_ng == p_ng) {

		/*

		 * Do not swap within a group or between tasks that have

		 * no group if there is spare capacity. Swapping does

		 * not address the load imbalance and helps one task at

		 * the cost of punishing another.

		 */

		if (env->dst_stats.node_type == node_has_spare)

			goto unlock;



		imp = taskimp + task_weight(cur, env->src_nid, dist) -

		      task_weight(cur, env->dst_nid, dist);

		/*