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From: Gregory Haskins <ghaskins@novell.com>
To: mingo@elte.hu
Cc: rostedt@goodmis.org, ghaskins@novell.com,
	linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 13/23] Subject: SCHED - Pre-route RT tasks on wakeup
Date: Tue, 04 Dec 2007 15:45:31 -0500	[thread overview]
Message-ID: <20071204204531.3567.99493.stgit@novell1.haskins.net> (raw)
In-Reply-To: <20071204204236.3567.65491.stgit@novell1.haskins.net>

In the original patch series that Steven Rostedt and I worked on together,
we both took different approaches to low-priority wakeup path.  I utilized
"pre-routing" (push the task away to a less important RQ before activating)
approach, while Steve utilized a "post-routing" approach.  The advantage of
my approach is that you avoid the overhead of a wasted activate/deactivate
cycle and peripherally related burdens.  The advantage of Steve's method is
that it neatly solves an issue preventing a "pull" optimization from being
deployed.

In the end, we ended up deploying Steve's idea.  But it later dawned on me
that we could get the best of both worlds by deploying both ideas together,
albeit slightly modified.

The idea is simple:  Use a "light-weight" lookup for pre-routing, since we
only need to approximate a good home for the task.  And we also retain the
post-routing push logic to clean up any inaccuracies caused by a condition
of "priority mistargeting" caused by the lightweight lookup.  Most of the
time, the pre-routing should work and yield lower overhead.  In the cases
where it doesnt, the post-router will bat cleanup.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
---

 kernel/sched_rt.c |   19 +++++++++++++++++++
 1 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 7e444f4..ea40851 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -149,8 +149,27 @@ yield_task_rt(struct rq *rq)
 }
 
 #ifdef CONFIG_SMP
+static int find_lowest_rq(struct task_struct *task);
+
 static int select_task_rq_rt(struct task_struct *p, int sync)
 {
+	struct rq *rq = task_rq(p);
+
+	/*
+	 * If the task will not preempt the RQ, try to find a better RQ
+	 * before we even activate the task
+	 */
+	if ((p->prio >= rq->rt.highest_prio)
+	    && (p->nr_cpus_allowed > 1)) {
+		int cpu = find_lowest_rq(p);
+
+		return (cpu == -1) ? task_cpu(p) : cpu;
+	}
+
+	/*
+	 * Otherwise, just let it ride on the affined RQ and the
+	 * post-schedule router will push the preempted task away
+	 */
 	return task_cpu(p);
 }
 #endif /* CONFIG_SMP */


  parent reply	other threads:[~2007-12-04 21:12 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-12-04 20:44 [PATCH 00/23] RT balance v7 Gregory Haskins
2007-12-04 20:44 ` [PATCH 01/23] Subject: SCHED - Add rt_nr_running accounting Gregory Haskins
2007-12-04 20:44 ` [PATCH 02/23] Subject: SCHED - track highest prio queued on runqueue Gregory Haskins
2007-12-04 20:44 ` [PATCH 03/23] Subject: SCHED - push RT tasks Gregory Haskins
2007-12-04 20:44 ` [PATCH 04/23] Subject: SCHED - RT overloaded runqueues accounting Gregory Haskins
2007-12-04 20:44 ` [PATCH 05/23] Subject: SCHED - pull RT tasks Gregory Haskins
2007-12-04 20:44 ` [PATCH 06/23] Subject: SCHED - wake up balance RT Gregory Haskins
2007-12-04 20:45 ` [PATCH 07/23] Subject: SCHED - disable CFS RT load balancing Gregory Haskins
2007-12-04 20:45 ` [PATCH 08/23] Subject: SCHED - Cache cpus_allowed weight for optimizing migration Gregory Haskins
2007-12-04 20:45 ` [PATCH 09/23] Subject: SCHED - Consistency cleanup for this_rq usage Gregory Haskins
2007-12-04 20:45 ` [PATCH 10/23] Subject: SCHED - Remove some CFS specific code from the wakeup path of RT tasks Gregory Haskins
2007-12-04 20:45 ` [PATCH 11/23] Subject: SCHED - Break out the search function Gregory Haskins
2007-12-04 20:45 ` [PATCH 12/23] Subject: SCHED - Allow current_cpu to be included in search Gregory Haskins
2007-12-04 20:45 ` Gregory Haskins [this message]
2007-12-04 20:45 ` [PATCH 14/23] Subject: SCHED - Optimize our cpu selection based on topology Gregory Haskins
2007-12-04 20:45 ` [PATCH 15/23] Subject: SCHED - Optimize rebalancing Gregory Haskins
2007-12-04 20:45 ` [PATCH 16/23] Subject: SCHED - Avoid overload Gregory Haskins
2007-12-04 20:45 ` [PATCH 17/23] Subject: SCHED - restore the migratable conditional Gregory Haskins
2007-12-04 20:45 ` [PATCH 18/23] Subject: SCHED - Optimize cpu search with hamming weight Gregory Haskins
2007-12-04 20:46 ` [PATCH 19/23] Subject: SCHED - Optimize out cpu_clears Gregory Haskins
2007-12-04 20:46 ` [PATCH 20/23] Subject: SCHED - balance RT tasks no new wake up Gregory Haskins
2007-12-04 20:46 ` [PATCH 21/23] Subject: SCHED - Add sched-domain roots Gregory Haskins
2007-12-04 20:46 ` [PATCH 22/23] Subject: SCHED - Only balance our RT tasks within our root-domain Gregory Haskins
2007-12-04 20:46 ` [PATCH 23/23] Subject: SCHED - Use a 2-d bitmap for searching lowest-pri CPU Gregory Haskins
2007-12-04 21:27 ` [PATCH 00/23] RT balance v7 Ingo Molnar
2007-12-04 21:35   ` Gregory Haskins
2007-12-05  2:55   ` [PATCH 0/3] RT balance v7a Gregory Haskins
2007-12-05  2:55     ` [PATCH 1/3] Subject: SCHED - Add sched-domain roots Gregory Haskins
2007-12-05  2:55     ` [PATCH 2/3] Subject: SCHED - Only balance our RT tasks within our root-domain Gregory Haskins
2007-12-05  2:55     ` [PATCH 3/3] Subject: SCHED - Use a 2-d bitmap for searching lowest-pri CPU Gregory Haskins
2007-12-05  9:34       ` Ingo Molnar
2007-12-05 10:19         ` Gregory Haskins
2007-12-05 11:44           ` Ingo Molnar
2007-12-05 13:41             ` Gregory Haskins

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