From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: Re: [PATCH v8 00/10] qspinlock: a 4-byte queue spinlock with PV support Date: Mon, 07 Apr 2014 12:38:13 -0400 Message-ID: <5342D475.7060503@hp.com> References: <1396445259-27670-1-git-send-email-Waiman.Long@hp.com> <5342425A.7040005@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5342425A.7040005@linux.vnet.ibm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Raghavendra K T Cc: linux-arch@vger.kernel.org, Rik van Riel , Gleb Natapov , kvm@vger.kernel.org, Konrad Rzeszutek Wilk , Peter Zijlstra , Scott J Norton , x86@kernel.org, Paolo Bonzini , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Ingo Molnar , Chegu Vinod , David Vrabel , "H. Peter Anvin" , xen-devel@lists.xenproject.org, Thomas Gleixner , "Paul E. McKenney" , Linus Torvalds , Oleg Nesterov , Aswin Chandramouleeswaran List-Id: linux-arch.vger.kernel.org On 04/07/2014 02:14 AM, Raghavendra K T wrote: > > > I tested the v7,v8 of qspinlock with unfair config on kvm guest. > I was curious about unfair locks performance in undercommit cases. > (overcommit case is expected to perform well) > > But I am seeing hang in overcommit cases. Gdb showed that many vcpus > are halted and there was no progress. Suspecting the problem /race with > halting, I removed the halt() part of kvm_hibernate(). I am yet to > take a closer look at the code on halt() related changes. It seems like there may still be race conditions where the current code is not handling correctly. I will look into that to see where the problem is. BTW, what test do you use to produce the hang condition? > > Patch series with that change gave around 20% improvement for dbench > 2x and 30% improvement for ebizzy 2x cases. (1x has no significant > loss/gain). > > What is the baseline for the performance improvement? Is it without the unfair lock and PV qspinlock? -Longman From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from g6t1525.atlanta.hp.com ([15.193.200.68]:49781 "EHLO g6t1525.atlanta.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755137AbaDGQie (ORCPT ); Mon, 7 Apr 2014 12:38:34 -0400 Message-ID: <5342D475.7060503@hp.com> Date: Mon, 07 Apr 2014 12:38:13 -0400 From: Waiman Long MIME-Version: 1.0 Subject: Re: [PATCH v8 00/10] qspinlock: a 4-byte queue spinlock with PV support References: <1396445259-27670-1-git-send-email-Waiman.Long@hp.com> <5342425A.7040005@linux.vnet.ibm.com> In-Reply-To: <5342425A.7040005@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Raghavendra K T Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Peter Zijlstra , linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, Paolo Bonzini , Konrad Rzeszutek Wilk , "Paul E. McKenney" , Rik van Riel , Linus Torvalds , David Vrabel , Oleg Nesterov , Gleb Natapov , Aswin Chandramouleeswaran , Scott J Norton , Chegu Vinod Message-ID: <20140407163813.PO9NxchrrzuowdWD1WYMC-qPFJFYdRufQne8QITgry0@z> On 04/07/2014 02:14 AM, Raghavendra K T wrote: > > > I tested the v7,v8 of qspinlock with unfair config on kvm guest. > I was curious about unfair locks performance in undercommit cases. > (overcommit case is expected to perform well) > > But I am seeing hang in overcommit cases. Gdb showed that many vcpus > are halted and there was no progress. Suspecting the problem /race with > halting, I removed the halt() part of kvm_hibernate(). I am yet to > take a closer look at the code on halt() related changes. It seems like there may still be race conditions where the current code is not handling correctly. I will look into that to see where the problem is. BTW, what test do you use to produce the hang condition? > > Patch series with that change gave around 20% improvement for dbench > 2x and 30% improvement for ebizzy 2x cases. (1x has no significant > loss/gain). > > What is the baseline for the performance improvement? Is it without the unfair lock and PV qspinlock? -Longman