Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758920AbYGJUzR (ORCPT ); Thu, 10 Jul 2008 16:55:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754123AbYGJUzD (ORCPT ); Thu, 10 Jul 2008 16:55:03 -0400 Received: from gw.goop.org ([64.81.55.164]:57392 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753940AbYGJUzB (ORCPT ); Thu, 10 Jul 2008 16:55:01 -0400 Message-ID: <48767717.9030100@goop.org> Date: Thu, 10 Jul 2008 13:54:47 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: "Eric W. Biederman" 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 Subject: Re: [RFC 00/15] x86_64: Optimize percpu accesses 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> <48766967.7040008@goop.org> In-Reply-To: X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1343 Lines: 34 Eric W. Biederman wrote: > Jeremy Fitzhardinge writes: > > >> No, that sounds like a bad idea. For one, how would you enforce it? How would >> you check for it? It's one of those things that would mostly work and then fail >> very rarely. >> > > Well the easiest way would be to avoid the letting people take the address of > per cpu memory, and just provide macros to read/write it. We are 90% of the > way there already so it isn't a big jump. > Well, the x86_X_percpu api is there. But per_cpu() and get_cpu_var() both explicitly return lvalues which can have their addresses taken. >> Secondly, I depend on it. I register a percpu structure with Xen to share >> per-vcpu specific information (interrupt mask, time info, runstate stats, etc). >> > > Well even virtual allocation is likely to break the Xen sharing case as you > would at least need to compute the physical address and pass it to Xen. > Right. At the moment it assumes that the percpu variable is in the linear mapping, but it could easily do a pagetable walk if necessary. J -- 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/