linux-kernel - [PATCH 3/3] temp hack to make tick based schedule happen

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Date:   Thu, 25 Jul 2019 22:33:44 +0800
From:   Aaron Lu <aaron.lu@...ux.alibaba.com>
To:     Aubrey Li <aubrey.intel@...il.com>
Cc:     Julien Desfossez <jdesfossez@...italocean.com>,
        Subhra Mazumdar <subhra.mazumdar@...cle.com>,
        Vineeth Remanan Pillai <vpillai@...italocean.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul Turner <pjt@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Frédéric Weisbecker <fweisbec@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kerr <kerrnel@...gle.com>, Phil Auld <pauld@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 3/3] temp hack to make tick based schedule happen

When a hyperthread is forced idle and the other hyperthread has a single
CPU intensive task running, the running task can occupy the hyperthread
for a long time with no scheduling point and starve the other
hyperthread.

Fix this temporarily by always checking if the task has exceed its
timeslice and if so, do a schedule.

Signed-off-by: Aaron Lu <ziqian.lzq@...fin.com>
---
 kernel/sched/fair.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 43babc2a12a5..730c9359e9c9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4093,6 +4093,9 @@ check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
 		return;
 	}
 
+	if (cfs_rq->nr_running <= 1)
+		return;
+
 	/*
 	 * Ensure that a task that missed wakeup preemption by a
 	 * narrow margin doesn't have to wait for a full slice.
@@ -4261,8 +4264,7 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
 		return;
 #endif
 
-	if (cfs_rq->nr_running > 1)
-		check_preempt_tick(cfs_rq, curr);
+	check_preempt_tick(cfs_rq, curr);
 }
 
 
-- 
2.19.1.3.ge56e4f7