linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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 18/23] Subject: SCHED - Optimize cpu search with hamming weight
Date: Tue, 04 Dec 2007 15:45:56 -0500	[thread overview]
Message-ID: <20071204204556.3567.19342.stgit@novell1.haskins.net> (raw)
In-Reply-To: <20071204204236.3567.65491.stgit@novell1.haskins.net>

We can cheaply track the number of bits set in the cpumask for the lowest
priority CPUs.  Therefore, compute the mask's weight and use it to skip
the optimal domain search logic when there is only one CPU available.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
---

 kernel/sched_rt.c |   25 ++++++++++++++++++-------
 1 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index fe0b43f..0514b27 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -301,7 +301,7 @@ static int find_lowest_cpus(struct task_struct *task, cpumask_t *lowest_mask)
 	int       cpu;
 	cpumask_t *valid_mask = &__get_cpu_var(valid_cpu_mask);
 	int       lowest_prio = -1;
-	int       ret         = 0;
+	int       count       = 0;
 
 	cpus_clear(*lowest_mask);
 	cpus_and(*valid_mask, cpu_online_map, task->cpus_allowed);
@@ -314,7 +314,7 @@ static int find_lowest_cpus(struct task_struct *task, cpumask_t *lowest_mask)
 
 		/* We look for lowest RT prio or non-rt CPU */
 		if (rq->rt.highest_prio >= MAX_RT_PRIO) {
-			if (ret)
+			if (count)
 				cpus_clear(*lowest_mask);
 			cpu_set(rq->cpu, *lowest_mask);
 			return 1;
@@ -326,14 +326,17 @@ static int find_lowest_cpus(struct task_struct *task, cpumask_t *lowest_mask)
 			if (rq->rt.highest_prio > lowest_prio) {
 				/* new low - clear old data */
 				lowest_prio = rq->rt.highest_prio;
-				cpus_clear(*lowest_mask);
+				if (count) {
+					cpus_clear(*lowest_mask);
+					count = 0;
+				}
 			}
 			cpu_set(rq->cpu, *lowest_mask);
-			ret = 1;
+			count++;
 		}
 	}
 
-	return ret;
+	return count;
 }
 
 static inline int pick_optimal_cpu(int this_cpu, cpumask_t *mask)
@@ -357,9 +360,17 @@ static int find_lowest_rq(struct task_struct *task)
 	cpumask_t *lowest_mask = &__get_cpu_var(local_cpu_mask);
 	int this_cpu = smp_processor_id();
 	int cpu      = task_cpu(task);
+	int count    = find_lowest_cpus(task, lowest_mask);
 
-	if (!find_lowest_cpus(task, lowest_mask))
-		return -1;
+	if (!count)
+		return -1; /* No targets found */
+
+	/*
+	 * There is no sense in performing an optimal search if only one
+	 * target is found.
+	 */
+	if (count == 1)
+		return first_cpu(*lowest_mask);
 
 	/*
 	 * At this point we have built a mask of cpus representing the


  parent reply	other threads:[~2007-12-04 21:13 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 ` [PATCH 13/23] Subject: SCHED - Pre-route RT tasks on wakeup Gregory Haskins
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 ` Gregory Haskins [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20071204204556.3567.19342.stgit@novell1.haskins.net \
    --to=ghaskins@novell.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-rt-users@vger.kernel.org \
    --cc=mingo@elte.hu \
    --cc=rostedt@goodmis.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).