linux-kernel - [tip: sched/urgent] sched/eevdf: Fix miscalculation in reweight

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Message-ID: <171378597395.10875.4756338867265230405.tip-bot2@tip-bot2>
Date: Mon, 22 Apr 2024 11:39:33 -0000
From: "tip-bot2 for Tianchen Ding" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Tianchen Ding <dtcccc@...ux.alibaba.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Abel Wu <wuyun.abel@...edance.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: sched/urgent] sched/eevdf: Fix miscalculation in
 reweight_entity() when se is not curr

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     afae8002b4fd3560c8f5f1567f3c3202c30a70fa
Gitweb:        https://git.kernel.org/tip/afae8002b4fd3560c8f5f1567f3c3202c30a70fa
Author:        Tianchen Ding <dtcccc@...ux.alibaba.com>
AuthorDate:    Wed, 06 Mar 2024 10:21:33 +08:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Mon, 22 Apr 2024 13:01:26 +02:00

sched/eevdf: Fix miscalculation in reweight_entity() when se is not curr

reweight_eevdf() only keeps V unchanged inside itself. When se !=
cfs_rq->curr, it would be dequeued from rb tree first. So that V is
changed and the result is wrong. Pass the original V to reweight_eevdf()
to fix this issue.

Fixes: eab03c23c2a1 ("sched/eevdf: Fix vruntime adjustment on reweight")
Signed-off-by: Tianchen Ding <dtcccc@...ux.alibaba.com>
[peterz: flip if() condition for clarity]
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Abel Wu <wuyun.abel@...edance.com>
Link: https://lkml.kernel.org/r/20240306022133.81008-3-dtcccc@linux.alibaba.com
---
 kernel/sched/fair.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5551ce2..6d26691 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3676,11 +3676,10 @@ static inline void
 dequeue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) { }
 #endif
 
-static void reweight_eevdf(struct cfs_rq *cfs_rq, struct sched_entity *se,
+static void reweight_eevdf(struct sched_entity *se, u64 avruntime,
 			   unsigned long weight)
 {
 	unsigned long old_weight = se->load.weight;
-	u64 avruntime = avg_vruntime(cfs_rq);
 	s64 vlag, vslice;
 
 	/*
@@ -3787,24 +3786,26 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
 			    unsigned long weight)
 {
 	bool curr = cfs_rq->curr == se;
+	u64 avruntime;
 
 	if (se->on_rq) {
 		/* commit outstanding execution time */
 		update_curr(cfs_rq);
+		avruntime = avg_vruntime(cfs_rq);
 		if (!curr)
 			__dequeue_entity(cfs_rq, se);
 		update_load_sub(&cfs_rq->load, se->load.weight);
 	}
 	dequeue_load_avg(cfs_rq, se);
 
-	if (!se->on_rq) {
+	if (se->on_rq) {
+		reweight_eevdf(se, avruntime, weight);
+	} else {
 		/*
 		 * Because we keep se->vlag = V - v_i, while: lag_i = w_i*(V - v_i),
 		 * we need to scale se->vlag when w_i changes.
 		 */
 		se->vlag = div_s64(se->vlag * se->load.weight, weight);
-	} else {
-		reweight_eevdf(cfs_rq, se, weight);
 	}
 
 	update_load_set(&se->load, weight);