Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754100AbaBTRyS (ORCPT ); Thu, 20 Feb 2014 12:54:18 -0500 Received: from g2t2354.austin.hp.com ([15.217.128.53]:33528 "EHLO g2t2354.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752341AbaBTRyQ (ORCPT ); Thu, 20 Feb 2014 12:54:16 -0500 X-Greylist: delayed 147823 seconds by postgrey-1.27 at vger.kernel.org; Thu, 20 Feb 2014 12:54:16 EST Message-ID: <5306413F.3010106@hp.com> Date: Thu, 20 Feb 2014 12:54:07 -0500 From: Waiman Long User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.12) Gecko/20130109 Thunderbird/10.0.12 MIME-Version: 1.0 To: Linus Torvalds CC: Peter Zijlstra , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , Arnd Bergmann , "linux-arch@vger.kernel.org" , the arch/x86 maintainers , Linux Kernel Mailing List , Steven Rostedt , Andrew Morton , Michel Lespinasse , Andi Kleen , Rik van Riel , "Paul E. McKenney" , 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: Content-Type: text/plain; charset=UTF-8; format=flowed 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 03:17 PM, Linus Torvalds wrote: > On Wed, Feb 19, 2014 at 11:24 AM, Waiman Long wrote: >> 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. > I could care less for the paravirt case. As long as the native case > ends up being sane (even when CONFIG_PARAVIRT is set at compile time), > I'm fine. > > When actually running in a paravirtualized environment, locks are > always going to have problems. > > Linus I think we could implement 2 versions of _raw_spin_lock. The primary one is fair and the other one is unfair with a jump label that jump from the fair version to the unfair version. At boot time, the kernel can check to see it is really running in a PV environment and then activate the jump label to use the unfair version. Now the key is how to detect if a kernel is really running in a PV environment. I need to ask some virtualization experts on that. -Longman -- 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/