From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756684AbbAFTag (ORCPT ); Tue, 6 Jan 2015 14:30:36 -0500 Received: from casper.infradead.org ([85.118.1.10]:56403 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754079AbbAFTad (ORCPT ); Tue, 6 Jan 2015 14:30:33 -0500 Date: Tue, 6 Jan 2015 20:30:25 +0100 From: Peter Zijlstra To: Tim Chen Cc: Ingo Molnar , Andi Kleen , Shawn Bohrer , Steven Rostedt , Suruchi Kadu , Doug Nelson , linux-kernel@vger.kernel.org, Juri Lelli Subject: Re: [PATCH] Repost sched-rt: Reduce rq lock contention by eliminating locking of non-feasible target Message-ID: <20150106193025.GD23965@worktop.programming.kicks-ass.net> References: <1420570911.2399.4.camel@schen9-desk2.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1420570911.2399.4.camel@schen9-desk2.jf.intel.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 06, 2015 at 11:01:51AM -0800, Tim Chen wrote: > Didn't get any response for this patch probably due to the holidays. > Reposting it as we will like to get it merged to help our database > workload. > > This patch added checks that prevent futile attempts to move rt tasks > to 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%. Don't immediately see anything wrong with this, Steve? Juri, do we want to do a similar thing to the dl bits? > Signed-off-by: Tim Chen > --- > kernel/sched/rt.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > index ee15f5a..0e4382e 100644 > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -1337,7 +1337,8 @@ select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags) > curr->prio <= p->prio)) { > int target = find_lowest_rq(p); > > - if (target != -1) > + if (target != -1 && > + p->prio < cpu_rq(target)->rt.highest_prio.curr) > cpu = target; > } > rcu_read_unlock(); > @@ -1613,6 +1614,12 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq) > break; > > lowest_rq = cpu_rq(cpu); > + > + if (lowest_rq->rt.highest_prio.curr <= task->prio) { > + /* target rq has tasks of equal or higher priority, try again */ > + lowest_rq = NULL; > + continue; > + } > > /* if the prio of this runqueue changed, try again */ > if (double_lock_balance(rq, lowest_rq)) { > -- > 1.8.3.1 > >