linux-kernel - Re: [PATCH RFC] sched/fair: fix sudden expiration of cfq quota in put_prev

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Date:	Tue, 7 Apr 2015 17:12:46 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Ben Segall <bsegall@...gle.com>,
	Roman Gushchin <klamm@...dex-team.ru>
Subject: Re: [PATCH RFC] sched/fair: fix sudden expiration of cfq quota in
 put_prev_task()

On Tue, Apr 07, 2015 at 03:47:58PM +0200, Peter Zijlstra wrote:
> Lemme think a bit more on that.

So going by 734ff2a71f9e ("sched/rt: Fix picking RT and DL tasks from
empty queue") something like this would be called for.

---
 kernel/sched/fair.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fdae26eb7218..1e47f816c976 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5175,6 +5175,21 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev)
 	return p;
 simple:
 	cfs_rq = &rq->cfs;
+
+	if (cfs_bandwidth_used()) {
+		/*
+		 * We may dequeue prev's cfs_rq in put_prev_task().
+		 * So, we update time before cfs_rq->nr_running check.
+		 */
+		if (prev->on_rq)
+			update_curr(cfs_rq);
+
+		se = &prev->se;
+		for_each_sched_entity(se) {
+			cfs_rq = cfs_rq_of(se);
+			check_cfs_rq_runtime(cfs_rq);
+		}
+	}
 #endif
 
 	if (!cfs_rq->nr_running)
--
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