Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754466AbcDAKbt (ORCPT ); Fri, 1 Apr 2016 06:31:49 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:35926 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751301AbcDAKbs (ORCPT ); Fri, 1 Apr 2016 06:31:48 -0400 Date: Fri, 1 Apr 2016 12:31:43 +0200 From: Peter Zijlstra To: Waiman Long Cc: Ingo Molnar , linux-kernel@vger.kernel.org, Scott J Norton , Douglas Hatch , Will Deacon Subject: Re: [PATCH] locking/qrwlock: Allow multiple spinning readers Message-ID: <20160401103143.GJ3448@twins.programming.kicks-ass.net> References: <1458444079-59601-1-git-send-email-Waiman.Long@hpe.com> <20160329202050.GN3408@twins.programming.kicks-ass.net> <56FDA0D6.4090904@hpe.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56FDA0D6.4090904@hpe.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 Content-Length: 570 Lines: 12 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.