From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757960AbbCCXXD (ORCPT ); Tue, 3 Mar 2015 18:23:03 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:36811 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757601AbbCCXVg (ORCPT ); Tue, 3 Mar 2015 18:21:36 -0500 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Tim Chen" , "Linus Torvalds" , "Suruchi Kadu" , "Steven Rostedt" , "Peter Zijlstra (Intel)" , "Doug Nelson" , "Shawn Bohrer" , "Ingo Molnar" Date: Tue, 03 Mar 2015 22:11:28 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 19/24] sched/rt: Reduce rq lock contention by eliminating locking of non-feasible target In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.249 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.68-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Tim Chen commit 80e3d87b2c5582db0ab5e39610ce3707d97ba409 upstream. This patch adds checks that prevens futile attempts to move rt tasks to a CPU with active tasks of equal or higher priority. This reduces run queue lock contention and improves the performance of a well known OLTP benchmark by 0.7%. Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Cc: Shawn Bohrer Cc: Suruchi Kadu Cc: Doug Nelson Cc: Steven Rostedt Cc: Linus Torvalds Link: http://lkml.kernel.org/r/1421430374.2399.27.camel@schen9-desk2.jf.intel.com Signed-off-by: Ingo Molnar [bwh: Backported to 3.2: adjust filename] Signed-off-by: Ben Hutchings --- kernel/sched_rt.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) --- a/kernel/sched_rt.c +++ b/kernel/sched_rt.c @@ -1067,7 +1067,12 @@ select_task_rq_rt(struct task_struct *p, (p->rt.nr_cpus_allowed > 1)) { int target = find_lowest_rq(p); - if (target != -1) + /* + * Don't bother moving it if the destination CPU is + * not running a lower priority task. + */ + if (target != -1 && + p->prio < cpu_rq(target)->rt.highest_prio.curr) cpu = target; } rcu_read_unlock(); @@ -1346,6 +1351,16 @@ static struct rq *find_lock_lowest_rq(st lowest_rq = cpu_rq(cpu); + if (lowest_rq->rt.highest_prio.curr <= task->prio) { + /* + * Target rq has tasks of equal or higher priority, + * retrying does not release any lock and is unlikely + * to yield a different result. + */ + lowest_rq = NULL; + break; + } + /* if the prio of this runqueue changed, try again */ if (double_lock_balance(rq, lowest_rq)) { /*