From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751552AbWGMOkp (ORCPT ); Thu, 13 Jul 2006 10:40:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751547AbWGMOko (ORCPT ); Thu, 13 Jul 2006 10:40:44 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:20625 "EHLO ebiederm.dsl.xmission.com") by vger.kernel.org with ESMTP id S1751555AbWGMOko (ORCPT ); Thu, 13 Jul 2006 10:40:44 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Ulrich Drepper Cc: "H. Peter Anvin" , Jakub Jelinek , Roland McGrath , Arjan van de Ven , "Randy.Dunlap" , akpm@osdl.org, linux-kernel@vger.kernel.org, libc-alpha@sourceware.org Subject: Re: [PATCH] Use uname not sysctl to get the kernel revision References: <20060712184412.2BD57180061@magilla.sf.frob.com> <44B54EA4.5060506@redhat.com> <20060712195349.GW3823@sunsite.mff.cuni.cz> <44B556E5.5000702@zytor.com> <44B5D77F.60200@redhat.com> Date: Thu, 13 Jul 2006 08:39:20 -0600 In-Reply-To: <44B5D77F.60200@redhat.com> (Ulrich Drepper's message of "Wed, 12 Jul 2006 22:17:51 -0700") Message-ID: User-Agent: Gnus/5.110004 (No Gnus v0.4) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Ulrich Drepper writes: > Eric W. Biederman wrote: >> Ulrich what would be interesting besides the possibility of having >> multiple cpus? > > What is needed for various things like memory handling etc is all > topology information. Somebody might remember the numa library proposal > I had in April 2004 which was cast aside because people were only > looking for a "quick fix". Well, the problem still isn't solved. > > IMO the vdso should export information about: > > - processors and their relationship (hyperthreads, cores) > > - the CPU caches and how they relate to the cores (e.g., dual core > with shared L2) > > - local main memory for each processor > > - relative costs of the memory access of the various memory regions > (for numa local memory to a node, intra-node costs) > > - ideally, relative costs main memory and CPU caches > > > All this information can be steadily updated by the kernel as new > CPUs/memory get added/removed. The vdso should have functions to access > this information. It's easy enough to make this access race free. > > I guess I should try to come up with a representation for this > knowledge. Collecting the information (except the costs) should be > easy. Determining the costs also shouldn't be that hard but it can be > very useful. Some of this information could be determined at userlevel > but you really don't want every process to compute all this from > scratch. And stored data in a file is stale if the system changes. The history of Linux shows that auto-tuning while not always perfect is much more effective than manual tuning. How are you envisioning using this information? I find it really easy to see how topology information can be used to manually tune a system. I don't currently see how it can be used to automatically tune a system. My fear is that we will end up making things brittle with user space over specifying things. I have another related concern about what rules need to be in place so I can upgrade the kernel vdso while a user space program is running. That make me seriously wonder how sane the vdso concept is, but that is a completely different issue. Eric