From owner-freebsd-arch Sun Oct 13 19:14:54 2002 Delivered-To: freebsd-arch@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id A826E37B401 for ; Sun, 13 Oct 2002 19:14:53 -0700 (PDT) Received: from harmony.village.org (rover.bsdimp.com [204.144.255.66]) by mx1.FreeBSD.org (Postfix) with ESMTP id E28CA43ECD for ; Sun, 13 Oct 2002 19:14:52 -0700 (PDT) (envelope-from imp@bsdimp.com) Received: from localhost (warner@rover2.village.org [10.0.0.1]) by harmony.village.org (8.12.3/8.12.3) with ESMTP id g9E2Empk021273; Sun, 13 Oct 2002 20:14:48 -0600 (MDT) (envelope-from imp@bsdimp.com) Date: Sun, 13 Oct 2002 20:14:27 -0600 (MDT) Message-Id: <20021013.201427.98861313.imp@bsdimp.com> To: dillon@apollo.backplane.com Cc: arch@FreeBSD.ORG Subject: Re: Database indexes and ram From: "M. Warner Losh" In-Reply-To: <200210131900.g9DJ0ZAM054777@apollo.backplane.com> References: <3DA9B4A8.194A02FC@mindspring.com> <20021013.120847.31902907.imp@bsdimp.com> <200210131900.g9DJ0ZAM054777@apollo.backplane.com> X-Mailer: Mew version 2.1 on Emacs 21.2 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-freebsd-arch@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG In message: <200210131900.g9DJ0ZAM054777@apollo.backplane.com> Matthew Dillon writes: : Google is your friend. I found a quick reference on the PCI bus. : A 32 bit PCI bus can support 64 bit addresses through the use of : two address cycles prefacing the data transfer. Right, but the cards have to support it as well, and most of the pci cards extant today simply do not support 64-bit operations. The 64-bit bit in BARS is set to 0 (well, more accuratelly, the decode size field is set to 00 or 01, meaning 4G or 1M of decode logic respectively). This means that most of them are incapible of generating the 64-bit addresses needed to do dma above 4G. Maybe the bridge chipsets support it, but very few cards do (and none of the ones that I've brushed up against, but I tend to get cards at the low end of the spectrum). Warner To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message