Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934077AbbDIJIk (ORCPT ); Thu, 9 Apr 2015 05:08:40 -0400 Received: from mail.kernel.org ([198.145.29.136]:43925 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933729AbbDII60 (ORCPT ); Thu, 9 Apr 2015 04:58:26 -0400 From: lizf@kernel.org To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Tim Chen , "Peter Zijlstra (Intel)" , Shawn Bohrer , Suruchi Kadu , Doug Nelson , Steven Rostedt , Linus Torvalds , Ingo Molnar , Zefan Li Subject: [PATCH 3.4 167/176] sched/rt: Reduce rq lock contention by eliminating locking of non-feasible target Date: Thu, 9 Apr 2015 16:46:55 +0800 Message-Id: <1428569224-23820-167-git-send-email-lizf@kernel.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1428569028-23762-1-git-send-email-lizf@kernel.org> References: <1428569028-23762-1-git-send-email-lizf@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2341 Lines: 72 From: Tim Chen 3.4.107-rc1 review patch. If anyone has any objections, please let me know. ------------------ 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 Signed-off-by: Zefan Li --- kernel/sched/rt.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 526c77d..71429db 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1293,7 +1293,12 @@ select_task_rq_rt(struct task_struct *p, int sd_flag, int flags) (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(); @@ -1570,6 +1575,16 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq) 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)) { /* -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/