From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: Preemptable Ticket Spinlock Date: Mon, 22 Apr 2013 22:08:14 +0200 Message-ID: <1366661294.6454.18.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> 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: <517595FA.800@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Mon, 2013-04-22 at 15:56 -0400, Rik van Riel wrote: > On 04/22/2013 03:49 PM, Peter Zijlstra wrote: > > On Mon, 2013-04-22 at 08:52 -0400, Rik van Riel wrote: > > >> If the native spin_lock code has been called already at > >> that time, the native code would still need to be modified > >> to increment the ticket number by 2, so we end up with a > >> compatible value in each spin lock's .tickets field, and > >> prevent a deadlock after we switch over to the paravirt > >> variant. > > > > I thought the stuff already made it upstream, but apparently not; the > > lastest posting I'm aware of is here: > > > > https://lkml.org/lkml/2012/5/2/105 > > > > That stuff changes the normal ticket increment as well.. > > Jiannan, > > It looks like the patch above could make a good patch > 1 (or 2) in your patch series :) I much prefer the entire series from Jeremy since it maintains the ticket semantics and doesn't degrade the lock to unfair under contention. Now I suppose there's a reason its not been merged yet and I suspect its !paravirt hotpath impact which wasn't rightly justified or somesuch so maybe someone can work on that or so.. dunno.