linux-kernel - [PATCH v2 5/6] sched/dl: Optimize select_task_rq

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Message-Id: <1415099585-31174-5-git-send-email-pang.xunlei@linaro.org>
Date:	Tue,  4 Nov 2014 19:13:04 +0800
From:	"pang.xunlei" <pang.xunlei@...aro.org>
To:	linux-kernel@...r.kernel.org
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Juri Lelli <juri.lelli@...il.com>,
	"pang.xunlei" <pang.xunlei@...aro.org>
Subject: [PATCH v2 5/6] sched/dl: Optimize select_task_rq_dl() for non-DL curr task

When selecting the cpu for a waking DL task, if curr is a non-DL
task which is bound only on this cpu, then we can give it a chance
to select a different cpu for this DL task to avoid curr starving.

Signed-off-by: pang.xunlei <pang.xunlei@...aro.org>
---
 kernel/sched/deadline.c |   14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 7b0b2d2..1f64d4a 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -954,6 +954,9 @@ select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags)
 	struct task_struct *curr;
 	struct rq *rq;
 
+	if (p->nr_cpus_allowed == 1)
+		goto out;
+
 	if (sd_flag != SD_BALANCE_WAKE && sd_flag != SD_BALANCE_FORK)
 		goto out;
 
@@ -970,11 +973,14 @@ select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags)
 	 * can!) we prefer to send it somewhere else. On the
 	 * other hand, if it has a shorter deadline, we
 	 * try to make it stay here, it might be important.
+	 *
+	 * If the current task on @p's runqueue is a non-DL task,
+	 * and this task is bound on current runqueue, then try to
+	 * see if we can wake this DL task up on a different runqueue,
 	 */
-	if (unlikely(dl_task(curr)) &&
-	    (curr->nr_cpus_allowed < 2 ||
-	     !dl_entity_preempt(&p->dl, &curr->dl)) &&
-	    (p->nr_cpus_allowed > 1)) {
+	if (unlikely(curr->nr_cpus_allowed < 2) ||
+		unlikely(dl_task(curr) &&
+				!dl_entity_preempt(&p->dl, &curr->dl))) {
 		int target = find_later_rq(p);
 
 		if (target != -1)
-- 
1.7.9.5

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