From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Wagner Subject: Re: [PATCH 2/3] sched/deadline: fix bandwidth check/update when migrating tasks between exclusive cpusets Date: Fri, 19 Sep 2014 13:47:34 +0200 Message-ID: <541C17D6.5020608@bmw-carit.de> References: <1411118561-26323-1-git-send-email-juri.lelli@arm.com> <1411118561-26323-3-git-send-email-juri.lelli@arm.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1411118561-26323-3-git-send-email-juri.lelli@arm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Juri Lelli , peterz@infradead.org Cc: mingo@redhat.com, juri.lelli@gmail.com, raistlin@linux.it, michael@amarulasolutions.com, fchecconi@gmail.com, vincent@legout.info, luca.abeni@unitn.it, linux-kernel@vger.kernel.org, Li Zefan , cgroups@vger.kernel.org Hi, On 09/19/2014 11:22 AM, Juri Lelli wrote: > Exclusive cpusets are the only way users can restrict SCHED_DEADLINE tasks > affinity (performing what is commonly called clustered scheduling). > Unfortunately, such thing is currently broken for two reasons: > > - No check is performed when the user tries to attach a task to > an exlusive cpuset (recall that exclusive cpusets have an > associated maximum allowed bandwidth). > > - Bandwidths of source and destination cpusets are not correctly > updated after a task is migrated between them. > > This patch fixes both things at once, as they are opposite faces > of the same coin. > > The check is performed in cpuset_can_attach(), as there aren't any > points of failure after that function. The updated is split in two > halves. We first reserve bandwidth in the destination cpuset, after > we pass the check in cpuset_can_attach(). And we then release > bandwidth from the source cpuset when the task's affinity is > actually changed. Even if there can be time windows when sched_setattr() > may erroneously fail in the source cpuset, we are fine with it, as > we can't perfom an atomic update of both cpusets at once. > > Reported-by: Daniel Wagner Ack I have no special test for this, I just let my test running which was fixed by patch #1. Works fine though. I'll plan to write some test for this. Thanks, Daniel