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Message-ID: <e17d3d90440997b970067fe9eaf088903c65f41d.camel@gmx.de>
Subject: Re: [PATCH] sched/fair: Reschedule the cfs_rq when current is
 ineligible
From: Mike Galbraith <efault@gmx.de>
To: Chunxin Zang <spring.cxz@gmail.com>, mingo@redhat.com,
 peterz@infradead.org,  juri.lelli@redhat.com, vincent.guittot@linaro.org
Cc: dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, 
	mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, 
	linux-kernel@vger.kernel.org, yu.c.chen@intel.com, yangchen11@lixiang.com, 
	zhouchunhua@lixiang.com, zangchunxin@lixiang.com
Date: Sat, 25 May 2024 08:41:28 +0200
In-Reply-To: <20240524134011.270861-1-spring.cxz@gmail.com>
References: <20240524134011.270861-1-spring.cxz@gmail.com>
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On Fri, 2024-05-24 at 21:40 +0800, Chunxin Zang wrote:
> I found that some tasks have been running for a long enough time and
> have become illegal, but they are still not releasing the CPU. This
> will increase the scheduling delay of other processes. Therefore, I
> tried checking the current process in wakeup_preempt and entity_tick,
> and if it is illegal, reschedule that cfs queue.

My box gave making the XXX below reality a two thumbs up when fiddling
with the original unfettered and a bit harsh RUN_TO_PARITY.

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8a5b1ae0aa55..922834f172b0 100644
=2D-- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8413,12 +8413,13 @@ static void check_preempt_wakeup_fair(struct rq *r=
q, struct task_struct *p, int
 	update_curr(cfs_rq);

 	/*
-	 * XXX pick_eevdf(cfs_rq) !=3D se ?
+	 * Run @curr until it is no longer our best option.  Basing the preempt
+	 * decision on @curr reselection puts any previous decisions back on the
+	 * table in context "now", including granularity preservation decisions
+	 * by RUN_TO_PARITY.
 	 */
-	if (pick_eevdf(cfs_rq) =3D=3D pse)
-		goto preempt;
-
-	return;
+	if (pick_eevdf(cfs_rq) =3D=3D se)
+		return;

 preempt:
 	resched_curr(rq);