linux-kernel - [PATCH 3/4] sched/fair: Limit run to parity to the min slice of enqueued entities

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250613140514.2781138-4-vincent.guittot@linaro.org>
Date: Fri, 13 Jun 2025 16:05:13 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: mingo@...hat.com,
	peterz@...radead.org,
	juri.lelli@...hat.com,
	dietmar.eggemann@....com,
	rostedt@...dmis.org,
	bsegall@...gle.com,
	mgorman@...e.de,
	vschneid@...hat.com,
	linux-kernel@...r.kernel.org
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH 3/4] sched/fair: Limit run to parity to the min slice of enqueued entities

Run to parity ensures that current will get a chance to run its full
slice in one go but this can create large latency for entity with shorter
slice that has alreasy exausted its slice and wait to run the next one.

Clamp the run to parity duration to the shortest slice of all enqueued
entities.

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/fair.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 479b38dc307a..d8345219dfd4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -917,23 +917,32 @@ struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
 }
 
 /*
- * HACK, stash a copy of deadline at the point of pick in vlag,
- * which isn't used until dequeue.
+ * HACK, Set the vruntime, up to which the entity can run before picking
+ * another one, in vlag, which isn't used until dequeue.
+ * In case of run to parity, we use the shortest slice of the enqueued
+ * entities.
  */
 static inline void set_protect_slice(struct sched_entity *se)
 {
-	se->vlag = se->deadline;
+	u64 min_slice;
+
+	min_slice = cfs_rq_min_slice(cfs_rq_of(se));
+
+	if (min_slice != se->slice)
+		se->vlag = min(se->deadline, se->vruntime + calc_delta_fair(min_slice, se));
+	else
+		se->vlag = se->deadline;
 }
 
 static inline bool protect_slice(struct sched_entity *se)
 {
-	return se->vlag == se->deadline;
+	return ((s64)(se->vlag - se->vruntime) > 0);
 }
 
 static inline void cancel_protect_slice(struct sched_entity *se)
 {
 	if (protect_slice(se))
-		se->vlag = se->deadline + 1;
+		se->vlag = se->vruntime;
 }
 
 /*
-- 
2.43.0