Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762702AbYGJTWa (ORCPT ); Thu, 10 Jul 2008 15:22:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757987AbYGJTWG (ORCPT ); Thu, 10 Jul 2008 15:22:06 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:39652 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754207AbYGJTWE (ORCPT ); Thu, 10 Jul 2008 15:22:04 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Jeremy Fitzhardinge Cc: Mike Travis , "H. Peter Anvin" , Arjan van de Ven , Ingo Molnar , Andrew Morton , Christoph Lameter , Jack Steiner , linux-kernel@vger.kernel.org, Rusty Russell References: <20080709165129.292635000@polaris-admin.engr.sgi.com> <20080709200757.GD14009@elte.hu> <48751B57.8030605@goop.org> <20080709133958.612635f0@infradead.org> <4875231F.1020506@zytor.com> <487524A0.6020304@goop.org> <487529AE.3060505@zytor.com> <48753A71.2030006@zytor.com> <48763732.7020805@sgi.com> <48765B03.6020905@goop.org> Date: Thu, 10 Jul 2008 12:18:25 -0700 In-Reply-To: <48765B03.6020905@goop.org> (Jeremy Fitzhardinge's message of "Thu, 10 Jul 2008 11:54:59 -0700") Message-ID: User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-SA-Exim-Connect-IP: 24.130.11.59 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-DCC: XMission; sa02 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Jeremy Fitzhardinge X-Spam-Relay-Country: X-Spam-Report: * -1.8 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -0.7 BAYES_20 BODY: Bayesian spam probability is 5 to 20% * [score: 0.0838] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa02 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 XM_SPF_Neutral SPF-Neutral Subject: Re: [RFC 00/15] x86_64: Optimize percpu accesses X-SA-Exim-Version: 4.2 (built Thu, 03 Mar 2005 10:44:12 +0100) X-SA-Exim-Scanned: Yes (on mgr1.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 989 Lines: 24 Jeremy Fitzhardinge writes: > Eric W. Biederman wrote: >> I think we can get away with just simply realloc'ing the percpu area >> on each cpu. No fancy table manipulations required. Just update >> the base pointer in %gs and in someplace global. >> > > It's perfectly legitimate to take the address of a percpu variable and store it > somewhere. We can't move them around. Really? I guess there are cases where that makes sense. It is a pretty rare case though. Especially when you are not talking about doing it temporarily with preemption disabled. There are few enough users of the API I think we can certainly explore the cost of forbidding in the general case of storing the address of a percpu variable. Eric -- 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/