From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753846AbbJOQk0 (ORCPT ); Thu, 15 Oct 2015 12:40:26 -0400 Received: from eu-smtp-delivery-143.mimecast.com ([207.82.80.143]:55875 "EHLO eu-smtp-delivery-143.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753767AbbJOQkT convert rfc822-to-8bit (ORCPT ); Thu, 15 Oct 2015 12:40:19 -0400 Subject: Re: [PATCH] Fix migration of SCHED_DEADLINE tasks To: Luca Abeni , linux-kernel@vger.kernel.org References: <1444907357-13114-1-git-send-email-luca.abeni@unitn.it> Cc: Peter Zijlstra , Ingo Molnar , Wanpeng Li From: Juri Lelli Message-ID: <561FD6F3.4090209@arm.com> Date: Thu, 15 Oct 2015 17:40:19 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <1444907357-13114-1-git-send-email-luca.abeni@unitn.it> X-OriginalArrivalTime: 15 Oct 2015 16:40:16.0140 (UTC) FILETIME=[2BAFF4C0:01D10768] X-MC-Unique: xLa7dB7zSlOX2YLP8jzVSA-1 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Luca, On 15/10/15 12:09, Luca Abeni wrote: > Commit 9d5142624256 ("sched/deadline: Reduce rq lock contention by > eliminating locking of non-feasible target") broke select_task_rq_dl() > and find_lock_later_rq(), because it introduced a comparison between > the local task's deadline and dl.earliest_dl.curr of the remote queue. > However, if the remote runqueue does not contain any SCHED_DEADLINE > task its earliest_dl.curr is 0 (always smaller than the deadline of > the local task) and the remote runqueue is not selected for pushing. > As a result, if an application creates multiple SCHED_DEADLINE threads, > they will never be pushed to runqueues that do not already contain > SCHED_DEADLINE tasks. > This patches fixes the issue by checking if dl.earliest_dl.curr == 0. > > Signed-off-by: Luca Abeni > --- > kernel/sched/deadline.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index fc8f010..0d86d60 100644 > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -1066,8 +1066,9 @@ select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags) > int target = find_later_rq(p); > > if (target != -1 && > - dl_time_before(p->dl.deadline, > - cpu_rq(target)->dl.earliest_dl.curr)) > + (dl_time_before(p->dl.deadline, > + cpu_rq(target)->dl.earliest_dl.curr) || > + (cpu_rq(target)->dl.earliest_dl.curr == 0))) Can't we actually use dl.dl_nr_running here and below, so that we won't incur any wraparound problem? Thanks, - Juri > cpu = target; > } > rcu_read_unlock(); > @@ -1417,7 +1418,8 @@ static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq) > > later_rq = cpu_rq(cpu); > > - if (!dl_time_before(task->dl.deadline, > + if (later_rq->dl.earliest_dl.curr && > + !dl_time_before(task->dl.deadline, > later_rq->dl.earliest_dl.curr)) { > /* > * Target rq has tasks of equal or earlier deadline, >