From owner-freebsd-stable@FreeBSD.ORG Tue Oct 7 19:24:58 2008 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id CEA721065693 for ; Tue, 7 Oct 2008 19:24:58 +0000 (UTC) (envelope-from sthaug@nethelp.no) Received: from bizet.nethelp.no (bizet.nethelp.no [195.1.209.33]) by mx1.freebsd.org (Postfix) with SMTP id 0CBFD8FC0C for ; Tue, 7 Oct 2008 19:24:57 +0000 (UTC) (envelope-from sthaug@nethelp.no) Received: (qmail 87318 invoked from network); 7 Oct 2008 19:24:55 -0000 Received: from bizet.nethelp.no (HELO localhost) (195.1.209.33) by bizet.nethelp.no with SMTP; 7 Oct 2008 19:24:55 -0000 Date: Tue, 07 Oct 2008 21:24:55 +0200 (CEST) Message-Id: <20081007.212455.74712524.sthaug@nethelp.no> To: joe@osoft.us From: sthaug@nethelp.no In-Reply-To: <48EBAB50.5000707@osoft.us> References: <48EBAB50.5000707@osoft.us> X-Mailer: Mew version 3.3 on Emacs 21.3 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: freebsd-stable@freebsd.org Subject: Re: fxp performance with POLLING X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 07 Oct 2008 19:24:58 -0000 > However, ethernet at 100Mbit is 4B5B coded at a 125mhz rate. So the raw > synchronous data rate really is 12.5Mbytes/s. Minus the sync preamble > of 8 bytes per packet and the mandatory inter-frame-gap of 12 bytes > that's a physical layer rate of (12.5M * (1500/(1500+20))) or 12.34Mbyte/s. You need add Ethernet header (14 bytes) + CRC (4 bytes). This means you have a maximum data rate, assuming 1500 byte MTU, of 12.5M * 1500/1538 = 12.19 Mbyte/s. And for those used to powers of two, M here means one million, not 1048576. Steinar Haug, Nethelp consulting, sthaug@nethelp.no