Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752335AbcDMUyo (ORCPT ); Wed, 13 Apr 2016 16:54:44 -0400 Received: from g2t4618.austin.hp.com ([15.73.212.83]:43198 "EHLO g2t4618.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751306AbcDMUyn (ORCPT ); Wed, 13 Apr 2016 16:54:43 -0400 Message-ID: <1460580544.2709.31.camel@j-VirtualBox> Subject: Re: [PATCH v2] MCS spinlock: Use smp_cond_load_acquire() From: Jason Low To: Will Deacon Cc: Peter Zijlstra , Linus Torvalds , "linux-kernel@vger.kernel.org" , "mingo@redhat.com" , "paulmck@linux.vnet.ibm.com" , "Rudd, Terry (HP Cloud Systems Linux R&D)" , "Long, Wai Man" , "boqun.feng@gmail.com" , "dave@stgolabs.net" , kbuild test robot , "kbuild-all@01.org" , jason.low2@hpe.com Date: Wed, 13 Apr 2016 13:49:04 -0700 In-Reply-To: <20160413174302.GC21722@arm.com> References: <1460516537.2709.7.camel@j-VirtualBox> <20160413174302.GC21722@arm.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 969 Lines: 23 On Wed, 2016-04-13 at 10:43 -0700, Will Deacon wrote: > On Tue, Apr 12, 2016 at 08:02:17PM -0700, Jason Low wrote: > > For qspinlocks on ARM64, we would like to use WFE instead > > of purely spinning. Qspinlocks internally have lock > > contenders spin on an MCS lock. > > > > Update arch_mcs_spin_lock_contended() such that it uses > > the new smp_cond_load_acquire() so that ARM64 can also > > override this spin loop with its own implementation using WFE. > > > > On x86, it can also cheaper to use this than spinning on > > smp_load_acquire(). > > > > Signed-off-by: Jason Low > > FWIW, we just override arch_mcs_spin_lock_contended entirely for arch/arm/ > and use wfe there so we could do the same for arm64 in mainline already. Right, I was also thinking about that, although when we use smp_cond_load_acquire() in the generic implementation, would we just end up overriding it for the arch/arm64 version with the same thing? :) Jason