From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755515AbcDAKl3 (ORCPT ); Fri, 1 Apr 2016 06:41:29 -0400 Received: from foss.arm.com ([217.140.101.70]:59844 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752322AbcDAKl2 (ORCPT ); Fri, 1 Apr 2016 06:41:28 -0400 Date: Fri, 1 Apr 2016 11:41:19 +0100 From: Will Deacon To: Peter Zijlstra Cc: Waiman Long , Ingo Molnar , linux-kernel@vger.kernel.org, Scott J Norton , Douglas Hatch Subject: Re: [PATCH] locking/qrwlock: Allow multiple spinning readers Message-ID: <20160401104119.GA3604@arm.com> References: <1458444079-59601-1-git-send-email-Waiman.Long@hpe.com> <20160329202050.GN3408@twins.programming.kicks-ass.net> <56FDA0D6.4090904@hpe.com> <20160401103143.GJ3448@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160401103143.GJ3448@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 01, 2016 at 12:31:43PM +0200, Peter Zijlstra wrote: > On Thu, Mar 31, 2016 at 06:12:38PM -0400, Waiman Long wrote: > > >>However, if we allow a limited number of readers to spin on the > > >>lock simultaneously, we can eliminates some of the reader-to-reader > > >>latencies at the expense of a bit more cacheline contention and > > >>probably more power consumption. > > >So the embedded people might not like that much. > > > > It could be. It is always a compromise. > > So ARM is the only one that currently waits without spinning and could > care; so Will might have an opinion. One 'solution' would be to make > this an optional feature. Well, perhaps we could built this using the cmp-and-wait structure we spoke about a couple of months back. What happened with that? Is there something I need to go implement for ARM/arm64? Will