From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: Preemptable Ticket Spinlock Date: Mon, 22 Apr 2013 22:48:34 +0200 Message-ID: <1366663714.8337.12.camel@laptop> References: <51745650.9050204@redhat.com> <1366631460.4443.3.camel@laptop> <51753289.70406@redhat.com> <1366660147.6454.6.camel@laptop> <517595FA.800@redhat.com> <1366661294.6454.18.camel@laptop> <51759E43.2080003@redhat.com> <1366663475.8337.10.camel@laptop> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Jiannan Ouyang , LKML , Raghavendra K T , Avi Kivity , Gleb Natapov , Ingo Molnar , Marcelo Tosatti , Srikar , "H. Peter Anvin" , "Nikunj A. Dadhania" , KVM , Thomas Gleixner , Chegu Vinod , "Andrew M. Theurer" , Srivatsa Vaddagiri , Andrew Jones , Karen Noel To: Rik van Riel Return-path: In-Reply-To: <1366663475.8337.10.camel@laptop> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Mon, 2013-04-22 at 22:44 +0200, Peter Zijlstra wrote: > On Mon, 2013-04-22 at 16:32 -0400, Rik van Riel wrote: > > > > IIRC one of the reasons was that the performance improvement wasn't > > as obvious. Rescheduling VCPUs takes a fair amount of time, quite > > probably more than the typical hold time of a spinlock. > > IIRC it would spin for a while before blocking.. > > /me goes re-read some of that thread... > > Ah, its because PLE is curing most of it.. !PLE it had huge gains but > apparently nobody cares about !PLE hardware anymore :-) Hmm.. it looked like under light overcommit the paravirt ticket lock still had some gain (~10%) and of course it brings the fairness thing which is always good. I can only imagine the mess unfair + vcpu preemption can bring to guest tasks.