From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Wed, 16 Apr 2003 12:50:07 +0100 (BST) Received: from p508B5469.dip.t-dialin.net ([IPv6:::ffff:80.139.84.105]:3754 "EHLO dea.linux-mips.net") by linux-mips.org with ESMTP id ; Wed, 16 Apr 2003 12:50:06 +0100 Received: (from ralf@localhost) by dea.linux-mips.net (8.11.6/8.11.6) id h3GBo1p08217; Wed, 16 Apr 2003 13:50:01 +0200 Date: Wed, 16 Apr 2003 13:50:01 +0200 From: Ralf Baechle To: Steve Taylor Cc: linux-mips@linux-mips.org Subject: Re: Basic cache questions Message-ID: <20030416135001.A29679@linux-mips.org> References: <20030415221914.47873.qmail@web14503.mail.yahoo.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5.1i In-Reply-To: <20030415221914.47873.qmail@web14503.mail.yahoo.com>; from godzilla1357@yahoo.com on Tue, Apr 15, 2003 at 03:19:14PM -0700 Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 2074 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: ralf@linux-mips.org Precedence: bulk X-list: linux-mips On Tue, Apr 15, 2003 at 03:19:14PM -0700, Steve Taylor wrote: > Hello All, I am hoping some of you mips-linux gurus will be able to > help me give me some tips and help me get started on some cache stuff which > I want to do. (I know decently well about caches - but only at a > theoretical Hennessy & Patterson level - and have just started looking > under arch/mips/mm to familiarize myself with the mips-linux > implementation). Here's what I want to do - I have a CPU with 4 way SA I > and D caches, and I want to write a module that will lock a certain memory > region in these caches (for example, let's say I want to lock the ISR in > the I-cache). So my questions are > a) Is the kernel going to crash if I try to mess around with the caches > like locking out a particular way of the cache or something like that? > b) I'm sure there are many issues and > complications involved in this that I probably havent even thought of - > any obvious and/or subtle pitfalls? and c) Do you think locking out, say, > an entire way of a 4-way cache for a dedicated frequently used routine > improves or degrades overall system performance? General wisdom says locking is rarely a win but a loss unless you have particularly pathological access patterns which is not so likely with a 4-way cache. Cache locking is primarily useful if you are doing hard realtime stuff and need execution time deterministic to the absolute technical limit - even if at cost of latency and throughput. Linux being a general purpose UNIX clone is hardly the OS for such an application ... Ralf