From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755403Ab0F3KK2 (ORCPT ); Wed, 30 Jun 2010 06:10:28 -0400 Received: from claw.goop.org ([74.207.240.146]:57762 "EHLO claw.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755381Ab0F3KKZ (ORCPT ); Wed, 30 Jun 2010 06:10:25 -0400 Message-ID: <4C2B180E.9060104@goop.org> Date: Wed, 30 Jun 2010 12:10:22 +0200 From: Jeremy Fitzhardinge User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100430 Fedora/3.0.4-2.fc12 Lightning/1.0b2pre Thunderbird/3.0.4 MIME-Version: 1.0 To: Jan Beulich CC: Peter Zijlstra , "mingo@elte.hu" , "tglx@linutronix.de" , ksrinivasan , "linux-kernel@vger.kernel.org" , "hpa@zytor.com" Subject: Re: [PATCH 4/4, v2] x86: enlightenment for ticket spin locks - improve yield behavior on Xen References: <4C2A20E30200007800008A17@vpn.id2.novell.com> <1277885485.1868.74.camel@laptop> <4C2B21300200007800008BDC@vpn.id2.novell.com> In-Reply-To: <4C2B21300200007800008BDC@vpn.id2.novell.com> X-Enigmail-Version: 1.0.1 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/30/2010 10:49 AM, Jan Beulich wrote: >>>> On 30.06.10 at 10:11, Peter Zijlstra wrote: >>>> >> On Tue, 2010-06-29 at 15:35 +0100, Jan Beulich wrote: >> >>> The (only) additional overhead this introduces for native execution is >>> the writing of the owning CPU in the lock acquire paths. >>> >> Uhm, and growing the size of spinlock_t to 6 (or 8 bytes when aligned) >> bytes when NR_CPUS>256. >> > Indeed, I should have mentioned that. Will do so in an eventual > next version. > Rather than increasing the lock size, why not just disable the enlightenment if the number of (possible) cpus is > 256? I don't think a VM will ever have that many cpus, so it will only apply in the case of booting the kernel on large physical machine. J