Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752666Ab3E3LwC (ORCPT ); Thu, 30 May 2013 07:52:02 -0400 Received: from e28smtp04.in.ibm.com ([122.248.162.4]:57078 "EHLO e28smtp04.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751860Ab3E3Lvw (ORCPT ); Thu, 30 May 2013 07:51:52 -0400 Message-ID: <51A73E5C.4010608@linux.vnet.ibm.com> Date: Thu, 30 May 2013 17:26:12 +0530 From: Raghavendra K T Organization: IBM User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121029 Thunderbird/16.0.2 MIME-Version: 1.0 To: Peter Zijlstra CC: Rik van Riel , Jiannan Ouyang , LKML , 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 , Konrad Rzeszutek Wilk Subject: Re: Preemptable Ticket Spinlock References: <51745650.9050204@redhat.com> <1366631460.4443.3.camel@laptop> <51753289.70406@redhat.com> <1366660147.6454.6.camel@laptop> <5175E71F.8070307@linux.vnet.ibm.com> In-Reply-To: <5175E71F.8070307@linux.vnet.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13053011-5564-0000-0000-0000082373FD Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3159 Lines: 79 On 04/23/2013 07:12 AM, Raghavendra K T wrote: > On 04/23/2013 01:19 AM, Peter Zijlstra wrote: >> On Mon, 2013-04-22 at 08:52 -0400, Rik van Riel wrote: >>> On 04/22/2013 07:51 AM, Peter Zijlstra wrote: >>>> On Sun, 2013-04-21 at 17:12 -0400, Rik van Riel wrote: >>>>> >>>>> If we always incremented the ticket number by 2 (instead of 1), then >>>>> we could use the lower bit of the ticket number as the spinlock. >>>> >>>> ISTR that paravirt ticket locks already do that and use the lsb to >>>> indicate the unlock needs to perform wakeups. >>>> >>>> Also, since all of this is virt nonsense, shouldn't it live in the >>>> paravirt ticket lock code and leave the native code as is? >>> >>> Sure, but that is still no reason not to have the virt >>> implementation be as fast as possible, and share the same >>> data type as the non-virt implementation. >> >> It has to share the same data-type.. >> >>> Also, is it guaranteed that the native spin_lock code has >>> not been called yet before we switch over to the paravirt >>> functions? >>> >>> 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.. >> > > pv-ticket spinlock went on hold state, after Avi acked because of: > > though on non-PLE, we get a huge advantage, on PLE machine the benefit > was not as impressive (~10% as you stated in email chain) compared to > the complexity of the patches. > So Avi suggested to try PLE improvements first, so they are going upstream. > > https://lkml.org/lkml/2012/7/18/247 > https://lkml.org/lkml/2013/1/22/104 > https://lkml.org/lkml/2013/2/6/345 (on the way in kvm tree) > > Current status of PV spinlock: > I have the rebased patches of pv spinlocks and experimenting with latest > kernel.I have > Gleb's irq delivery incorporated into the patch series. But I am > thinknig whether I can > improve some guest side logic in unlock. > I will probably setup a githup and post the link soon. Sorry for late reply. Here is the branch with pvpspinlock V9 version in github reabsed to 3.10-rc https://github.com/ktraghavendra/linux/tree/pvspinlock_v9 planning post a formal email in a separate thread with link a to this branch (instead of spamming with 19 patches) Main changes w.r.t v8 are - Changed spin_threshold to 32k to avoid excess halt exits that are causing undercommit degradation (after PLE handler improvement). - Added kvm_irq_delivery_to_apic (suggested by Gleb) - optimized halt exit path to use PLE handler -- 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/