From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753339Ab3H0NxY (ORCPT ); Tue, 27 Aug 2013 09:53:24 -0400 Received: from merlin.infradead.org ([205.233.59.134]:34210 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753062Ab3H0NxX (ORCPT ); Tue, 27 Aug 2013 09:53:23 -0400 Date: Tue, 27 Aug 2013 15:53:10 +0200 From: Peter Zijlstra To: Steven Rostedt Cc: Alexander Fyodorov , Waiman Long , linux-kernel , "Chandramouleeswaran, Aswin" , "Norton, Scott J" , Thomas Gleixner , Ingo Molnar , "Paul E. McKenney" Subject: Re: [PATCH RFC v2 1/2] qspinlock: Introducing a 4-byte queue spinlock implementation Message-ID: <20130827135309.GF10002@twins.programming.kicks-ass.net> References: <15321377012704@web8h.yandex.ru> <52142D6C.6000400@hp.com> <336901377100289@web16f.yandex.ru> <5215638E.5020702@hp.com> <169431377178121@web21f.yandex.ru> <521BB71F.6080300@hp.com> <66111377605355@web12m.yandex.ru> <20130827091436.3d5971a0@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130827091436.3d5971a0@gandalf.local.home> 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 Tue, Aug 27, 2013 at 09:14:36AM -0400, Steven Rostedt wrote: > I just had this conversation with Paul McKenney. Should there be a > smp_mb_after_spin_unlock()? Depends on the benefits I suppose :-) Oleg and Linus did recently add smp_mb__before_spinlock(); > Although we blew it off as adding too many extensions to smp_mb(). But > it may be better than reimplementing something as complex as a lock. Locks should be as light weight as possible and never implement anything heavier than the ACQUISITION / RELEASE barriers if at all possible. We should certainly not re-implement spinlocks just to get full barriers out of them, that's crazy.