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From: Mel Gorman <mgorman@techsingularity.net>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Phil Auld <pauld@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
	Mel Gorman <mgorman@techsingularity.net>
Subject: [PATCH 08/11] sched/numa: Bias swapping tasks based on their preferred node
Date: Wed, 12 Feb 2020 09:36:51 +0000	[thread overview]
Message-ID: <20200212093654.4816-9-mgorman@techsingularity.net> (raw)
In-Reply-To: <20200212093654.4816-1-mgorman@techsingularity.net>

When swapping tasks for NUMA balancing, it is preferred that tasks move
to or remain on their preferred node. When considering an imbalance,
encourage tasks to move to their preferred node and discourage tasks from
moving away from their preferred node.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
 kernel/sched/fair.c | 44 ++++++++++++++++++++++++++++++++++++++------
 1 file changed, 38 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3f518b0d9261..24fc90b8036a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1707,18 +1707,27 @@ static void task_numa_compare(struct task_numa_env *env,
 			goto unlock;
 	}
 
+	/* Skip this swap candidate if cannot move to the source cpu. */
+	if (!cpumask_test_cpu(env->src_cpu, cur->cpus_ptr))
+		goto unlock;
+
+	/*
+	 * Skip this swap candidate if it is not moving to its preferred
+	 * node and the best task is.
+	 */
+	if (env->best_task &&
+	    env->best_task->numa_preferred_nid == env->src_nid &&
+	    cur->numa_preferred_nid != env->src_nid) {
+		goto unlock;
+	}
+
 	/*
 	 * "imp" is the fault differential for the source task between the
 	 * source and destination node. Calculate the total differential for
 	 * the source task and potential destination task. The more negative
 	 * the value is, the more remote accesses that would be expected to
 	 * be incurred if the tasks were swapped.
-	 */
-	/* Skip this swap candidate if cannot move to the source cpu */
-	if (!cpumask_test_cpu(env->src_cpu, cur->cpus_ptr))
-		goto unlock;
-
-	/*
+	 *
 	 * If dst and source tasks are in the same NUMA group, or not
 	 * in any group then look only at task weights.
 	 */
@@ -1745,12 +1754,35 @@ static void task_numa_compare(struct task_numa_env *env,
 			       task_weight(cur, env->dst_nid, dist);
 	}
 
+	/* Discourage picking a task already on its preferred node */
+	if (cur->numa_preferred_nid == env->dst_nid)
+		imp -= imp / 16;
+
+	/*
+	 * Encourage picking a task that moves to its preferred node.
+	 * This potentially makes imp larger than it's maximum of
+	 * 1998 (see SMALLIMP and task_weight for why) but in this
+	 * case, it does not matter.
+	 */
+	if (cur->numa_preferred_nid == env->src_nid)
+		imp += imp / 8;
+
 	if (maymove && moveimp > imp && moveimp > env->best_imp) {
 		imp = moveimp;
 		cur = NULL;
 		goto assign;
 	}
 
+	/*
+	 * If a swap is required then prefer moving a task to its preferred
+	 * nid over a task that is not moving to a preferred nid.
+	 */
+	if (cur->numa_preferred_nid == env->src_nid && env->best_task &&
+	    env->best_task->numa_preferred_nid != env->src_nid) {
+		goto assign;
+	}
+
+
 	/*
 	 * If the NUMA importance is less than SMALLIMP,
 	 * task migration might only result in ping pong
-- 
2.16.4


  parent reply	other threads:[~2020-02-12  9:37 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-12  9:36 [RFC PATCH 00/11] Reconcile NUMA balancing decisions with the load balancer Mel Gorman
2020-02-12  9:36 ` [PATCH 01/11] sched/fair: Allow a small load imbalance between low utilisation SD_NUMA domains Mel Gorman
2020-02-12  9:36 ` [PATCH 02/11] sched/fair: Optimize select_idle_core() Mel Gorman
2020-02-12  9:36 ` [PATCH 03/11] sched/fair: Allow a per-CPU kthread waking a task to stack on the same CPU, to fix XFS performance regression Mel Gorman
2020-02-12  9:36 ` [PATCH 04/11] sched/numa: Trace when no candidate CPU was found on the preferred node Mel Gorman
2020-02-12  9:36 ` [PATCH 05/11] sched/numa: Distinguish between the different task_numa_migrate failure cases Mel Gorman
2020-02-12 14:43   ` Steven Rostedt
2020-02-12 15:59     ` Mel Gorman
2020-02-12  9:36 ` [PATCH 06/11] sched/numa: Prefer using an idle cpu as a migration target instead of comparing tasks Mel Gorman
2020-02-12  9:36 ` [PATCH 07/11] sched/numa: Find an alternative idle CPU if the CPU is part of an active NUMA balance Mel Gorman
2020-02-12  9:36 ` Mel Gorman [this message]
2020-02-13 10:31   ` [PATCH 08/11] sched/numa: Bias swapping tasks based on their preferred node Peter Zijlstra
2020-02-13 11:18     ` Mel Gorman
2020-02-12 13:22 ` [RFC PATCH 00/11] Reconcile NUMA balancing decisions with the load balancer Vincent Guittot
2020-02-12 14:07   ` Valentin Schneider
2020-02-12 15:48   ` Mel Gorman
2020-02-12 16:13     ` Vincent Guittot
2020-02-12 15:45 ` [PATCH 09/11] sched/fair: Split out helper to adjust imbalances between domains Mel Gorman
2020-02-12 15:46 ` [PATCH 10/11] sched/numa: Use similar logic to the load balancer for moving between domains with spare capacity Mel Gorman
2020-02-12 15:46 ` [PATCH 11/11] sched/numa: Use similar logic to the load balancer for moving between overloaded domains Mel Gorman
     [not found] ` <20200214041232.18904-1-hdanton@sina.com>
2020-02-14  7:50   ` [PATCH 08/11] sched/numa: Bias swapping tasks based on their preferred node Mel Gorman

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