Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753237AbaBSVat (ORCPT ); Wed, 19 Feb 2014 16:30:49 -0500 Received: from terminus.zytor.com ([198.137.202.10]:59253 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751858AbaBSVas (ORCPT ); Wed, 19 Feb 2014 16:30:48 -0500 Message-ID: <5305222B.4080706@zytor.com> Date: Wed, 19 Feb 2014 13:29:15 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Waiman Long , Peter Zijlstra CC: Thomas Gleixner , Ingo Molnar , Arnd Bergmann , linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Steven Rostedt , Andrew Morton , Michel Lespinasse , Andi Kleen , Rik van Riel , "Paul E. McKenney" , Linus Torvalds , Raghavendra K T , George Spelvin , Tim Chen , Daniel J Blueman , Alexander Fyodorov , Aswin Chandramouleeswaran , Scott J Norton , Thavatchai Makphaibulchoke Subject: Re: [PATCH v4 0/3] qspinlock: Introducing a 4-byte queue spinlock References: <1392669684-4807-1-git-send-email-Waiman.Long@hp.com> <53029167.4060109@zytor.com> <20140218073111.GW27965@twins.programming.kicks-ass.net> <5303B4C4.2040907@hp.com> <20140218212827.GR14089@laptop.programming.kicks-ass.net> <5303FDEC.9060001@hp.com> <20140219085107.GG27965@twins.programming.kicks-ass.net> <53050501.3070101@hp.com> In-Reply-To: <53050501.3070101@hp.com> X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/19/2014 11:24 AM, Waiman Long wrote: > On 02/19/2014 03:51 AM, Peter Zijlstra wrote: >> On Tue, Feb 18, 2014 at 07:42:20PM -0500, Waiman Long wrote: >>> On 02/18/2014 04:28 PM, Peter Zijlstra wrote: >>>> On Tue, Feb 18, 2014 at 02:30:12PM -0500, Waiman Long wrote: >>>>> I will start looking at how to make it work with paravirt. >>>>> Hopefully, it >>>>> won't take too long. >>>> The cheap way out is to simply switch to the test-and-set spinlock on >>>> whatever X86_FEATURE_ indicates a guest I suppose. >>> I don't think there is X86_FEATURE flag that indicates running in a >>> guest. >>> In fact, a guest should never find out if it is running virtualized. >> No it very much should; how else is paravirt ever going to work? > > We do have a CONFIG_PARAVIRT macro that turns on or off PV support. The > queue spinlock can be easily changed into an unfair lock which allows > lock stealing. We could have a config option to make it unfair in the > PARAVIRT environment, but I don't think Linus like the idea of an unfair > lock. > The case where we run native on a system with CONFIG_PARAVIRT enabled DOES matter. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/