From owner-freebsd-alpha Tue Sep 1 09:36:17 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id JAA07038 for freebsd-alpha-outgoing; Tue, 1 Sep 1998 09:36:17 -0700 (PDT) (envelope-from owner-freebsd-alpha@FreeBSD.ORG) Received: from feral.com (gw100.feral.com [192.67.166.129]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id JAA07030 for ; Tue, 1 Sep 1998 09:36:15 -0700 (PDT) (envelope-from mjacob@feral.com) Received: from localhost (mjacob@localhost) by feral.com (8.8.6/8.8.6) with SMTP id JAA18244; Tue, 1 Sep 1998 09:35:12 -0700 Date: Tue, 1 Sep 1998 09:35:12 -0700 (PDT) From: Matthew Jacob X-Sender: mjacob@feral-gw Reply-To: mjacob@feral.com To: Andrew Gallatin cc: freebsd-alpha@FreeBSD.ORG Subject: Re: Alpha Install - oops! In-Reply-To: <13804.8316.576176.582569@grasshopper.cs.duke.edu> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-alpha@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org I wouldn't claim that it does or doesn't happen- I just would suspect this as being what a piece of h/w would do. It's probably a lot of gates and probably a big performance penalty to avoid prefetch across certain boundaries. As much as possible, I prefer direct map as well. On Tue, 1 Sep 1998, Andrew Gallatin wrote: > > Matthew Jacob writes: > > > > > > I'd watch this for crossing page boundaries on reads if you're using any > > S/G map stuff. In fact, I'd have an extra mapping at the end of > > the S/G list that just remaps the first page so that any prefetch > > on a read won't get a fault but will just pick up known good data. > > Gee, I'd hope a GL would be smart enough not to prefectch past the end > of a S/G segment; I do know that the page-boundry DMA restriction is gone on GL's. > > However, I use the direct-map segment in my Myrinet drivers (on DU & > on *BSD), so I can't verify that it doesn't happen. > > Drew > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-alpha" in the body of the message