linux-kernel - [PATCH v3] sched/eevdf: Force propagating min_slice of cfs

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Message-Id: <20250211063659.7180-1-dtcccc@linux.alibaba.com>
Date: Tue, 11 Feb 2025 14:36:59 +0800
From: Tianchen Ding <dtcccc@...ux.alibaba.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v3] sched/eevdf: Force propagating min_slice of cfs_rq when {en,de}queue tasks

When a task is enqueued and its parent cgroup se is already on_rq, this
parent cgroup se will not be enqueued again, and hence the root->min_slice
leaves unchanged. The same issue happens when a task is dequeued and its
parent cgroup se has other runnable entities, and the parent cgroup se
will not be dequeued.

Force propagating min_slice when se doesn't need to be enqueued or
dequeued. Ensure the se hierarchy always get the latest min_slice.

Fixes: aef6987d8954 ("sched/eevdf: Propagate min_slice up the cgroup hierarchy")
Signed-off-by: Tianchen Ding <dtcccc@...ux.alibaba.com>
---
v3:
I modified some descriptions in commit log, and rebased to the latest
tip branch. The old version of patch can be found in [1].

The original patchset wants to add a feature. As the 2nd patch may be
hard to be accepted, I think at least the bugfix should be applied.

The issue about this patch was described detailly in [2].

[1]https://lore.kernel.org/all/20241031094822.30531-1-dtcccc@linux.alibaba.com/
[2]https://lore.kernel.org/all/a903d0dc-1d88-4ae7-ac81-3eed0445654d@linux.alibaba.com/
---
 kernel/sched/fair.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1e78caa21436..0d479b92633a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6970,6 +6970,8 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 		update_cfs_group(se);
 
 		se->slice = slice;
+		if (se != cfs_rq->curr)
+			min_vruntime_cb_propagate(&se->run_node, NULL);
 		slice = cfs_rq_min_slice(cfs_rq);
 
 		cfs_rq->h_nr_runnable += h_nr_runnable;
@@ -7099,6 +7101,8 @@ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags)
 		update_cfs_group(se);
 
 		se->slice = slice;
+		if (se != cfs_rq->curr)
+			min_vruntime_cb_propagate(&se->run_node, NULL);
 		slice = cfs_rq_min_slice(cfs_rq);
 
 		cfs_rq->h_nr_runnable -= h_nr_runnable;
-- 
2.39.3