linux-kernel - [PATCH] sched/fair: avoid vruntime compensation for SCHED

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Message-Id: <20200820120025.74460-1-benbjiang@tencent.com>
Date:   Thu, 20 Aug 2020 20:00:25 +0800
From:   Jiang Biao <benbjiang@...il.com>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org
Cc:     dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, linux-kernel@...r.kernel.org,
        Jiang Biao <benbjiang@...cent.com>
Subject: [PATCH] sched/fair: avoid vruntime compensation for SCHED_IDLE task

From: Jiang Biao <benbjiang@...cent.com>

Vruntime compensation has been down in place_entity() to
boot the waking procedure for fair tasks. There is no need to
do that for SCHED_IDLE task actually.

Not compensating vruntime for SCHED_IDLE task could make
SCHED_IDLE task more harmless for normal tasks.

Signed-off-by: Jiang Biao <benbjiang@...cent.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 1a68a0536add..adff77676a0a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4115,7 +4115,7 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
 		vruntime += sched_vslice(cfs_rq, se);
 
 	/* sleeps up to a single latency don't count. */
-	if (!initial) {
+	if (!initial && likely(!task_has_idle_policy(task_of(se)))) {
 		unsigned long thresh = sysctl_sched_latency;
 
 		/*
-- 
2.21.0