From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH v9 06/19] qspinlock: prolong the stay in the pending bit path Date: Fri, 18 Apr 2014 10:33:42 +0200 Message-ID: <20140418083342.GA11096@twins.programming.kicks-ass.net> References: <1397747051-15401-1-git-send-email-Waiman.Long@hp.com> <1397747051-15401-7-git-send-email-Waiman.Long@hp.com> <20140417163640.GT11096@twins.programming.kicks-ass.net> <535083DC.2040406@hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <535083DC.2040406@hp.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: Waiman Long Cc: linux-arch@vger.kernel.org, Rik van Riel , Raghavendra K T , Gleb Natapov , kvm@vger.kernel.org, Konrad Rzeszutek Wilk , 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 List-Id: linux-arch.vger.kernel.org On Thu, Apr 17, 2014 at 09:46:04PM -0400, Waiman Long wrote: > BTW, I didn't test out your atomic_test_and_set() change. Did it provide a > noticeable performance benefit when compared with cmpxchg()? I've not tested that I think. I had a hard time showing that cmpxchg loops were slower, but once I did, I simply replaced all cmpxchg loops with unconditional ops where possible. The machine that was big enough to show it lived in a lab half way around the world and using it was a right pain in the ass, so I didn't use it more than I absolutely had to. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from merlin.infradead.org ([205.233.59.134]:59045 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751034AbaDRId4 (ORCPT ); Fri, 18 Apr 2014 04:33:56 -0400 Date: Fri, 18 Apr 2014 10:33:42 +0200 From: Peter Zijlstra Subject: Re: [PATCH v9 06/19] qspinlock: prolong the stay in the pending bit path Message-ID: <20140418083342.GA11096@twins.programming.kicks-ass.net> References: <1397747051-15401-1-git-send-email-Waiman.Long@hp.com> <1397747051-15401-7-git-send-email-Waiman.Long@hp.com> <20140417163640.GT11096@twins.programming.kicks-ass.net> <535083DC.2040406@hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <535083DC.2040406@hp.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Waiman Long Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , 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 , Raghavendra K T , David Vrabel , Oleg Nesterov , Gleb Natapov , Scott J Norton , Chegu Vinod Message-ID: <20140418083342.dlCOxk9kLc7Q2WwtlJgoqT8UP3hviBtitimnnFAiiIA@z> On Thu, Apr 17, 2014 at 09:46:04PM -0400, Waiman Long wrote: > BTW, I didn't test out your atomic_test_and_set() change. Did it provide a > noticeable performance benefit when compared with cmpxchg()? I've not tested that I think. I had a hard time showing that cmpxchg loops were slower, but once I did, I simply replaced all cmpxchg loops with unconditional ops where possible. The machine that was big enough to show it lived in a lab half way around the world and using it was a right pain in the ass, so I didn't use it more than I absolutely had to.