From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933320Ab0KOUFb (ORCPT ); Mon, 15 Nov 2010 15:05:31 -0500 Received: from terminus.zytor.com ([198.137.202.10]:40182 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756552Ab0KOUFa (ORCPT ); Mon, 15 Nov 2010 15:05:30 -0500 Message-ID: <4CE1920F.5000509@zytor.com> Date: Mon, 15 Nov 2010 12:03:27 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.12) Gecko/20101027 Fedora/3.1.6-1.fc13 Thunderbird/3.1.6 MIME-Version: 1.0 To: Jeremy Fitzhardinge CC: Peter Zijlstra , Linux Kernel Mailing List , Jan Beulich , Avi Kivity , Xen-devel , Linux Virtualization , Srivatsa Vaddagiri , Mathieu Desnoyers Subject: Re: [PATCH 00/20] x86: ticket lock rewrite and paravirtualization References: <4CDDBBD3.5050903@zytor.com> <4CDDBCE4.80906@goop.org> <4CDDBDB5.8000800@zytor.com> <4CE1915F.60507@goop.org> In-Reply-To: <4CE1915F.60507@goop.org> 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 11/15/2010 12:00 PM, Jeremy Fitzhardinge wrote: > > Another approach I discussed with PeterZ and Mathieu is to steal the LSB > of the ticket counters (halving the max CPU count) to use as a "there is > someone in slowpath waiting on this lock". But I haven't spent the time > to work out an algorithm to maintain that flag (or flags, since there > are bits available) in a correct and efficient way. > Definitely worth pondering. -hpa