From owner-freebsd-net Tue May 9 3:36:57 2000 Delivered-To: freebsd-net@freebsd.org Received: from ccserv.csie.nctu.edu.tw (ccserv.csie.nctu.edu.tw [140.113.209.2]) by hub.freebsd.org (Postfix) with ESMTP id 0FFF637BDFB for ; Tue, 9 May 2000 03:36:39 -0700 (PDT) (envelope-from freedom@ccserv.csie.nctu.edu.tw) Received: (from freedom@localhost) by ccserv.csie.nctu.edu.tw (8.9.3/8.9.0) id SAA28511; Tue, 9 May 2000 18:35:48 +0800 (CST) Date: Tue, 9 May 2000 18:35:48 +0800 From: Tan Koan-Sin To: Theo PAGTZIS Cc: freebsd-net@freebsd.org Subject: Re: Question on Tx queueing internals Message-ID: <20000509183548.A19208@ccserv.csie.nctu.edu.tw> References: <3917DF55.9ABD99AD@cs.ucl.ac.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 1.0i In-Reply-To: <3917DF55.9ABD99AD@cs.ucl.ac.uk>; from T.Pagtzis@cs.ucl.ac.uk on Tue, May 09, 2000 at 10:50:14AM +0100 Sender: owner-freebsd-net@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org On Tue, May 09, 2000 at 10:50:14AM +0100, Theo PAGTZIS wrote: > I am told that on the network card there is a Tx and Rx buffer.... > Is the output queue of an interface driver the same thing as a transmit > buffer on the actual network card or are they two different things...ie > when the ip_output passes the packet to the if_output function of the > Ether interface, the if_output will add the Ether header and then put it > on the output queue (if_snd). Is this output queue (the driver's output > queue ) the same as what one call the Tx/Rx buffer on the network card > or are is it a different one? They are different. The if_snd is a mbuf linked list in main memory. The Tx/Rx buffers are on the card. Take the Intel 82559 (fxp) on FreeBSD as a example, the Tx and Rx buffer on the network card are separate 3K FIFOs. > Also is the Tx buffer a different piece of memory than the Rx buffer on > the Ethernet card. I am asking that trying to understand whethe Tx and > Rx share a single buffer on the card so that Tx buffer could starv Rx > buffering... It depends the card you use. You must find the data sheet of the chips used on your card. -- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message