Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755254Ab3DVUcc (ORCPT ); Mon, 22 Apr 2013 16:32:32 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50905 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754895Ab3DVUcb (ORCPT ); Mon, 22 Apr 2013 16:32:31 -0400 Message-ID: <51759E43.2080003@redhat.com> Date: Mon, 22 Apr 2013 16:32:03 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130402 Thunderbird/17.0.5 MIME-Version: 1.0 To: Peter Zijlstra 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 Subject: Re: Preemptable Ticket Spinlock 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> In-Reply-To: <1366661294.6454.18.camel@laptop> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1690 Lines: 43 On 04/22/2013 04:08 PM, Peter Zijlstra wrote: > 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. 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. -- All rights reversed -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/