Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758586AbYGJQqI (ORCPT ); Thu, 10 Jul 2008 12:46:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751576AbYGJQp4 (ORCPT ); Thu, 10 Jul 2008 12:45:56 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:50307 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750833AbYGJQpz (ORCPT ); Thu, 10 Jul 2008 12:45:55 -0400 Message-ID: <48763CA6.9030802@linux-foundation.org> Date: Thu, 10 Jul 2008 11:45:26 -0500 From: Christoph Lameter User-Agent: Thunderbird 2.0.0.14 (Windows/20080421) MIME-Version: 1.0 To: "H. Peter Anvin" CC: Jeremy Fitzhardinge , "Eric W. Biederman" , Ingo Molnar , Mike Travis , Andrew Morton , Jack Steiner , linux-kernel@vger.kernel.org, Arjan van de Ven 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> <48751CF9.4020901@linux-foundation.org> <4875209D.8010603@goop.org> <48752CCD.30507@linux-foundation.org> <48753C99.5050408@goop.org> <487555A8.2050007@zytor.com> <487556A5.5090907@goop.org> <4876194E.4080205@linux-foundation.org> <48761C06.3020003@zytor.com> <48762A3B.5050104@linux-foundation.org> <48762DD2.5090802@zytor.com> <487637A1.4080403@linux-foundation.org> <487639ED.7000502@zytor.com> In-Reply-To: <487639ED.7000502@zytor.com> 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 Content-Length: 1370 Lines: 31 H. Peter Anvin wrote: > It will, but it might still be a net loss due to higher load on the TLB > (you're effectively using the TLB to do the table lookup for you.) On > the other hand, Mike points out that once we move away from fixed-sized > segments we pretty much have to use virtual addresses anyway(*). There will be no additional overhead since the memory already mapped 1-1 using 2MB TLBs and we want to use the same for the percpu areas. This is similar to the vmemmap solution. >> The first percpu area would ideally be the per cpu segment generated >> by the linker. >> >> How would that fit into the address map? In particular the 2G distance >> between code and the first per cpu area must not be violated unless we >> go to a zero based approach. > > If with "zero-based" you mean "nonzero gs_base for the boot CPU" then > yes, you're right. > > Note again that that is completely orthogonal to RIP-based versus absolute. ?? The distance to the per cpu area for cpu 0 is larger than 2G. Kernel wont link with RIP based addresses. You would have to place the per cpu areas 1TB before the kernel text. -- 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/