From owner-freebsd-hackers Sun Mar 14 11:20:49 1999 Delivered-To: freebsd-hackers@freebsd.org Received: from apollo.backplane.com (apollo.backplane.com [209.157.86.2]) by hub.freebsd.org (Postfix) with ESMTP id AF15314F08 for ; Sun, 14 Mar 1999 11:20:47 -0800 (PST) (envelope-from dillon@apollo.backplane.com) Received: (from dillon@localhost) by apollo.backplane.com (8.9.3/8.9.1) id LAA93395; Sun, 14 Mar 1999 11:20:28 -0800 (PST) (envelope-from dillon) Date: Sun, 14 Mar 1999 11:20:28 -0800 (PST) From: Matthew Dillon Message-Id: <199903141920.LAA93395@apollo.backplane.com> To: Amancio Hasty Cc: Wes Peters , Cory Kempf , Bill Paul , freebsd-hackers@FreeBSD.ORG Subject: Re: Gigabit ethernet -- what am I doing wrong? References: <199903140927.BAA85633@rah.star-gate.com> Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG :> cannot be done. So routing a single packet requires the data to flow :> over the PCI bus twice. The 132 MBytes/sec become 66 MBytes/sec right :> off the bat. : :I am not sure that I can follow you here . Most PCI cards which are capable of :doing dma to the host system's memory can do card - to - card transfer :;however, :the target "card" most be able to use the stored data in the case of a network :card it must have memory to receive the pack or a very elaborate protocol :to accept short dma bursts which it can then process. : : : Amancio You can always do a card-to-card transfer, but since most modern network cards do *NOT* have on-card memory doing a card-to-card transfer typically doesn't work. For example, if the destination card hits a collision/retry, the source card's FIFO can overflow. It just doesn't work. Using a card as a DMA destination only works well for cards that map memory, such as a video card. -Matt Matthew Dillon To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message