From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: Re: what is the expeted performance from a dual port 10G card ? Date: Sat, 29 Nov 2008 17:34:43 +0000 Message-ID: <20081129173442.GI32518@solarflare.com> References: <5d96567b0811280511q1e3f7774j7eabce4810dae91a@mail.gmail.com> <20081128135419.GH32518@solarflare.com> <5d96567b0811290010r641388b7w179bc4af26bbf103@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org To: Raz Return-path: Received: from smarthost02.mail.zen.net.uk ([212.23.3.141]:58535 "EHLO smarthost02.mail.zen.net.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751393AbYK2Ret (ORCPT ); Sat, 29 Nov 2008 12:34:49 -0500 Content-Disposition: inline In-Reply-To: <5d96567b0811290010r641388b7w179bc4af26bbf103@mail.gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: Raz wrote: > PCI Encoding overhead is 8 bits /10 bits . so 16Gbps supposed to be > the practical limit. The 8b10 encoding is already accounted for in the 2.5 Gbps figure; the raw bit rate is 3.125 Gbps. I'm thinking about the transaction layer overhead. Since PCI Express has few side-band signals there is a protocol a little like TCP running over the link, which adds a header to each request or response packet (TLP). The maximum TLP size is usually quite small so the header accounts for a fair proportion of the link bandwidth. > I still lack 3 Gbps in the Intel case. where are they ? That's for Intel to answer. Ben. -- Ben Hutchings, Senior Software Engineer, Solarflare Communications Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.