From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Rostedt Subject: Re: [RFC][PATCH RT 3/4] sched/rt: Use IPI to trigger RT task push migration instead of pulling Date: Tue, 11 Dec 2012 09:16:53 -0500 Message-ID: <1355235413.17101.293.camel@gandalf.local.home> References: <20121207235615.206108556@goodmis.org> <20121208000900.613917378@goodmis.org> <50C682F6.5030709@am.sony.com> <50C68922.5030203@am.sony.com> <1355190830.17101.280.camel@gandalf.local.home> <1355234577.17101.288.camel@gandalf.local.home> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-15" Content-Transfer-Encoding: 7bit Cc: frank.rowand@am.sony.com, "linux-kernel@vger.kernel.org" , linux-rt-users , Carsten Emde , John Kacur , Peter Zijlstra , Clark Williams , Ingo Molnar To: Thomas Gleixner Return-path: In-Reply-To: <1355234577.17101.288.camel@gandalf.local.home> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-rt-users.vger.kernel.org On Tue, 2012-12-11 at 09:02 -0500, Steven Rostedt wrote: > Currently, what we have is a huge contention on both the pulled CPU rq > lock. We've measured over 500us latencies due to it. This hurts even the > CPU that has the overloaded task, as the contention is on its lock. The 500us latency was one of the max ones I saw, and I believe it was combined with the load balancer going off at the same time as the pulls were happening. I've seen larger latencies with limited function tracing enabled and the load balancer was very involved. As I believe we have users that would very much want this in, and if you are still not sure you like this "feature" I can make it into a SCHED_FEAT() like TTWU_QUEUE. Then you can keep this off and the big boxes can enable them. Maybe enable the feature by default if the box has more than 16 cpus? -- Steve