From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752228AbaFWG6l (ORCPT ); Mon, 23 Jun 2014 02:58:41 -0400 Received: from casper.infradead.org ([85.118.1.10]:45903 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751767AbaFWG6j (ORCPT ); Mon, 23 Jun 2014 02:58:39 -0400 Date: Mon, 23 Jun 2014 08:58:35 +0200 From: Peter Zijlstra To: Davidlohr Bueso Cc: Ingo Molnar , Linus Torvalds , Heiko Carstens , Aswin Chandramouleeswaran , linux-kernel@vger.kernel.org Subject: Re: [PATCH] arch,locking: Ciao arch_mutex_cpu_relax() Message-ID: <20140623065835.GF19860@laptop.programming.kicks-ass.net> References: <1403288473.10903.2.camel@buesod1.americas.hpqcorp.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1403288473.10903.2.camel@buesod1.americas.hpqcorp.net> 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 Fri, Jun 20, 2014 at 11:21:13AM -0700, Davidlohr Bueso wrote: > From: Davidlohr Bueso > > The arch_mutex_cpu_relax() function, introduced by 34b133f, is > hacky and ugly. It was added a few years ago to address the fact > that common cpu_relax() calls include yielding on s390, and thus > impact the optimistic spinning functionality of mutexes. Nowadays > we use this function well beyond mutexes: rwsem, qrwlock, mcs and > lockref. Since the macro that defines the call is in the mutex header, > any users must include mutex.h and the naming is misleading as well. > > This patch (i) renames the call to arch_cpu_relax (for lack of a better > name), and (ii) defines it in each arch's asm/processor.h local header, > just like for regular cpu_relax() functions. On all archs, except s390, > arch_cpu_relax is simply cpu_relax, and thus we can take it out of > mutex.h. While this can seem redundant or weird, I believe it is a > good choice as it allows us to move out arch specific logic from generic > locking primitives and enables future(?) archs to transparently define > it, similarly to System Z. > > Please note that these changes are only tested on x86-64. While I like the general idea; does anyone have a better name for this? So in particular, the difference is that on s390: cpu_relax() - yields the vcpu arch_{,mutex_}cpu_relax() - will actually spin-wait