From owner-freebsd-hackers  Mon Mar 22 10:34:56 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 E0B4914C20
	for <hackers@FreeBSD.ORG>; Mon, 22 Mar 1999 10:34:54 -0800 (PST)
	(envelope-from dillon@apollo.backplane.com)
Received: (from dillon@localhost)
	by apollo.backplane.com (8.9.3/8.9.1) id KAA21361;
	Mon, 22 Mar 1999 10:34:27 -0800 (PST)
	(envelope-from dillon)
Date: Mon, 22 Mar 1999 10:34:27 -0800 (PST)
From: Matthew Dillon <dillon@apollo.backplane.com>
Message-Id: <199903221834.KAA21361@apollo.backplane.com>
To: Dennis <dennis@etinc.com>
Cc: Mike Smith <mike@smith.net.au>,
	Amancio Hasty <hasty@rah.star-gate.com>, hackers@FreeBSD.ORG
Subject: Re: Gigabit ethernet -- what am I doing wrong? 
References: <Your message of "Sun, 21 Mar 1999 20:10:21 EST."             <199903220058.TAA17538@etinc.com> <199903221711.MAA20551@etinc.com>
Sender: owner-freebsd-hackers@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.ORG


:>This has nothing whatever to do with reality, however.  Most PCI 
:>peripherals are bus masters, and most memory busses these days are at 
:>least 64 bits wide, so 64 bit PCI has very real performance benefits.
:>
:>The processor's internal word size has little or nothing to do with the 
:>equation.
:
:The ability to do single-cycle transfers IS affected by the internal
:processor's
:word size. If it can't do sustained single-cycle bursts then performance
:suffers
:significantly, so I disagree wholeheartedly on this. If the on-board processor
:doesnt  have a 64bit bus it is very difficult to do single cycle transfers.
:
:Dennis

    All PCI card chipsets implement internal read and write 
    DMA FIFO's.  Thus a 64 bit PCI card can easily burst 64 bit
    words over the PCI bus.  If the processor on the card
    itself cannot stuff the FIFO quickly enough to hold the burst
    for a period longer then the size of the FIFO, it's no big deal
    because the processor on the card can obviously pump data 
    sufficiently to handle the physical I/O it is supporting for
    that card , and the FIFO is large enough such that the 
    shorter higher-speed burst on the PCI bus will be sufficient
    enough to use the PCI bus bandwidth efficiently.  What bandwidth 
    cannot be used by one card will certainly be used by another.

    This just isn't an issue.

					-Matt
					Matthew Dillon 
					<dillon@backplane.com>


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message