Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261256AbTEMOIF (ORCPT ); Tue, 13 May 2003 10:08:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261260AbTEMOIF (ORCPT ); Tue, 13 May 2003 10:08:05 -0400 Received: from watch.techsource.com ([209.208.48.130]:62396 "EHLO techsource.com") by vger.kernel.org with ESMTP id S261256AbTEMOIE (ORCPT ); Tue, 13 May 2003 10:08:04 -0400 Message-ID: <3EC10074.8060806@techsource.com> Date: Tue, 13 May 2003 10:25:56 -0400 From: Timothy Miller User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.0.1) Gecko/20020823 Netscape/7.0 X-Accept-Language: en-us, en MIME-Version: 1.0 To: "H. Peter Anvin" CC: Ulrich Drepper , linux-kernel@vger.kernel.org Subject: Re: hammer: MAP_32BIT References: <3EBB5A44.7070704@redhat.com> <20030509092026.GA11012@averell> <16059.37067.925423.998433@gargle.gargle.HOWL> <20030509113845.GA4586@averell> <3EBC0084.4090809@redhat.com> <3EBC15B5.4070604@zytor.com> <3EBC2164.6050605@redhat.com> <3EBC29A5.1050005@techsource.com> <3EBC2996.2040908@zytor.com> <3EBC2FD7.2080007@techsource.com> <3EBC389C.2010601@zytor.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1515 Lines: 50 H. Peter Anvin wrote: > Timothy Miller wrote: > >>>The purpose is that there is a slight task-switching speed advantage if >>>the address is in the bottom 4 GB. Since this affects every process, >>>and most processes use very little TLS, this is worthwhile. >>> >>>This is fundamentally due to a K8 design flaw. >> >>Is there an explicit check somewhere for this? Are the page tables laid >>out differently? >> > > > No, there are two ways to load the FS base register: use a descriptor, > which is limited to 4 GB but is faster, or WRMSR, which is slower, but > unlimited. > Ulrich Drepper wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Timothy Miller wrote: > > >>Why does there ever need to be an explicit HINT that you would prefer a >><32 bit address, when it's known a priori that <32 is better? Why >>doesn't the mapping code ALWAYS try to use 32-bit addresses before >>resorting to 64-bit? > > > Because not all memory is addressed via GDT entries. In fact, almost > none is, only thread stacks and similar gimicks. If all mmap memory > would by default be served from the low memory pool you soon run out of > it and without any good reason. All I have to say is... I appreciate your patience with my ignorant questions. :) - 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/