From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Fri, 04 Oct 2002 13:53:43 +0200 (CEST) Received: from alg133.algor.co.uk ([62.254.210.133]:42210 "EHLO oval.algor.co.uk") by linux-mips.org with ESMTP id ; Fri, 4 Oct 2002 13:53:43 +0200 Received: from mudchute.algor.co.uk (pubfw.algor.co.uk [62.254.210.129]) by oval.algor.co.uk (8.11.6/8.10.1) with ESMTP id g94BrRr05492; Fri, 4 Oct 2002 12:53:28 +0100 (BST) Received: (from dom@localhost) by mudchute.algor.co.uk (8.8.5/8.8.5) id MAA12052; Fri, 4 Oct 2002 12:53:22 +0100 (BST) Date: Fri, 4 Oct 2002 12:53:22 +0100 (BST) Message-Id: <200210041153.MAA12052@mudchute.algor.co.uk> From: Dominic Sweetman MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit To: Carsten Langgaard Cc: Ralf Baechle , linux-mips@linux-mips.org Subject: Re: Promblem with PREF (prefetching) in memcpy In-Reply-To: <3D9D484B.4C149BD8@mips.com> References: <3D9D484B.4C149BD8@mips.com> X-Mailer: VM 6.34 under 19.16 "Lille" XEmacs Lucid 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: 353 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: dom@algor.co.uk Precedence: bulk X-list: linux-mips Carsten Langgaard (carstenl@mips.com) writes: > I think we have a problem with the PREF instructions spread out in the > memcpy function. Not really. The MIPS32 manual (for example): "PREF does not cause addressing-related exceptions. If it does happen to raise an exception condition, the exception condition is ignored. If an addressing-related exception condition is raised and ignored, no data movement occurs." PREF never generates a memory operation for a location with an uncached memory access type." For a Linux user program, at least, memory pages are "memory-like": reads are guaranteed to be side-effect free, so any outlying prefetches are harmless. It's hard to see any circumstance where an accessible cacheable location would lead to bad side-effects on read. -- Dominic Sweetman, MIPS Technologies (UK) - formerly Algorithmics The Fruit Farm, Ely Road, Chittering, CAMBS CB5 9PH, ENGLAND phone: +44 1223 706200 / fax: +44 1223 706250 / direct: +44 1223 706205 http://www.algor.co.uk