From owner-freebsd-hackers Fri Sep 21 23:59:32 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from avocet.mail.pas.earthlink.net (avocet.mail.pas.earthlink.net [207.217.121.50]) by hub.freebsd.org (Postfix) with ESMTP id 8A95237B41F; Fri, 21 Sep 2001 23:59:30 -0700 (PDT) Received: from dialup-209.245.141.15.dial1.sanjose1.level3.net ([209.245.141.15] helo=mindspring.com) by avocet.mail.pas.earthlink.net with esmtp (Exim 3.32 #2) id 15kgl4-0003XK-00; Fri, 21 Sep 2001 23:59:27 -0700 Message-ID: <3BAC36F4.1B9E8E2E@mindspring.com> Date: Sat, 22 Sep 2001 00:00:04 -0700 From: Terry Lambert Reply-To: tlambert2@mindspring.com X-Mailer: Mozilla 4.7 [en]C-CCK-MCD {Sony} (Win98; U) X-Accept-Language: en MIME-Version: 1.0 To: Luigi Rizzo Cc: Andrew Gallatin , hackers@freebsd.org, wpaul@freebsd.org Subject: Re: any reason to use m_devget in the "dc" driver ? References: <200109220558.HAA64949@info.iet.unipi.it> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG Luigi Rizzo wrote: > > I probably missed some emails ? > In any case i was only concerned about the additional copy > done by m_devget when the controller can already DMA into > an mbuf, and there are no alignment constraints. I guess we are talking about a protocol other than IP? The ethernet header is 14 bytes in length, which means that the elements in the IP header are not longword aligned, unless the card can DMA onto a 2 byte boundary, and does so, to ensure that the IP header starts on a 16 byte boundary, and therefore the contents are correctly aligned for direct reference in a single bus cycle (or at all, on Alpha, where unaligned access is not permitted). -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message