From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2992594AbXDDFSd (ORCPT ); Wed, 4 Apr 2007 01:18:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S2992631AbXDDFSd (ORCPT ); Wed, 4 Apr 2007 01:18:33 -0400 Received: from terminus.zytor.com ([192.83.249.54]:60614 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2992594AbXDDFSc (ORCPT ); Wed, 4 Apr 2007 01:18:32 -0400 Message-ID: <461334B5.7070607@zytor.com> Date: Tue, 03 Apr 2007 22:16:37 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 1.5.0.9 (X11/20070212) MIME-Version: 1.0 To: Eric Dumazet CC: Jeremy Fitzhardinge , Ulrich Drepper , Davide Libenzi , Linux Kernel , Andrew Morton , Andi Kleen Subject: Re: getting processor numbers References: <461286D6.2040407@redhat.com> <4612ABD7.3000201@redhat.com> <4612F1F0.5070209@zytor.com> <4612F2BF.7080704@goop.org> <4612F394.6040105@zytor.com> <4613330C.1020701@cosmosbay.com> In-Reply-To: <4613330C.1020701@cosmosbay.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Eric Dumazet wrote: > > There is one thing that always worried me. > > Intel & AMD manuals make clear that mixing data and program in the same > page is bad for performance. > > In particular, x86_64 vsyscall put jiffies and other > vsyscall_gtod_data_t right in the midle of code. That is certainly not > wise. > > A probably sane implementation should use two pages, one for code, one > for data. > Mutable data should be separated from code. I think any current CPU will do fine as long as they are in separate 128-byte chunks, but they need at least that much separation. Readonly data does not need to be separated from code. -hpa