linux-kernel - [PATCH] sched/fair: optimize the PLACE

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Message-Id: <20241001070021.10626-1-shijie@os.amperecomputing.com>
Date: Tue,  1 Oct 2024 15:00:21 +0800
From: Huang Shijie <shijie@...amperecomputing.com>
To: mingo@...hat.com,
	peterz@...radead.org,
	juri.lelli@...hat.com
Cc: patches@...erecomputing.com,
	vincent.guittot@...aro.org,
	dietmar.eggemann@....com,
	rostedt@...dmis.org,
	bsegall@...gle.com,
	mgorman@...e.de,
	vschneid@...hat.com,
	linux-kernel@...r.kernel.org,
	Huang Shijie <shijie@...amperecomputing.com>,
	Christoph Lameter <cl@...ux.com>
Subject: [PATCH] sched/fair: optimize the PLACE_LAG when se->vlag is zero

When PLACE_LAG is enabled, from the relationship:
            vl_i = (W + w_i)*vl'_i / W
we know that if vl'_i(se->vlag) is zero, the vl_i is zero too.

So if se->vlag is zero, there is no need to waste cycles to
do the calculation.

Reviewed-by: Christoph Lameter (Ampere) <cl@...ux.com>
Signed-off-by: Huang Shijie <shijie@...amperecomputing.com>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a7d8bb95e17c..1812c9cc079d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5280,7 +5280,7 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 	 *
 	 * EEVDF: placement strategy #1 / #2
 	 */
-	if (sched_feat(PLACE_LAG) && cfs_rq->nr_running) {
+	if (sched_feat(PLACE_LAG) && cfs_rq->nr_running && se->vlag) {
 		struct sched_entity *curr = cfs_rq->curr;
 		unsigned long load;
 
-- 
2.40.1