Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752129AbaDQPt1 (ORCPT ); Thu, 17 Apr 2014 11:49:27 -0400 Received: from merlin.infradead.org ([205.233.59.134]:58122 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751006AbaDQPtQ (ORCPT ); Thu, 17 Apr 2014 11:49:16 -0400 Date: Thu, 17 Apr 2014 17:49:02 +0200 From: Peter Zijlstra 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 Subject: Re: [PATCH v9 04/19] qspinlock: Extract out the exchange of tail code word Message-ID: <20140417154902.GO11096@twins.programming.kicks-ass.net> References: <1397747051-15401-1-git-send-email-Waiman.Long@hp.com> <1397747051-15401-5-git-send-email-Waiman.Long@hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1397747051-15401-5-git-send-email-Waiman.Long@hp.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 17, 2014 at 11:03:56AM -0400, Waiman Long wrote: > @@ -192,36 +220,25 @@ void queue_spin_lock_slowpath(struct qspinlock *lock, u32 val) > node->next = NULL; > > /* > + * We touched a (possibly) cold cacheline; attempt the trylock once > + * more in the hope someone let go while we weren't watching as long > + * as no one was queuing. > */ > + if (!(val & _Q_TAIL_MASK) && queue_spin_trylock(lock)) > + goto release; But you just did a potentially very expensive op; @val isn't representative anymore! -- 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/