From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: Re: [PATCH] bnx2x: tx-switching module parameter Date: Thu, 16 Feb 2012 17:20:40 +0000 Message-ID: <1329412840.2601.13.camel@bwh-desktop> References: <1329401112-9542-1-git-send-email-ariele@broadcom.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: , , Eilon Greenstein To: Ariel Elior Return-path: Received: from mail.solarflare.com ([216.237.3.220]:39162 "EHLO ocex02.SolarFlarecom.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753471Ab2BPRUn (ORCPT ); Thu, 16 Feb 2012 12:20:43 -0500 In-Reply-To: <1329401112-9542-1-git-send-email-ariele@broadcom.com> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, 2012-02-16 at 16:05 +0200, Ariel Elior wrote: > In 57712 and 578xx the tx-switching module parameter allows the user to control > whether outgoing traffic can be loopbacked into the device in case there is a > relevant client for the data using the same device for rx. > A classic example where this is necessary is for virtualization purposes, where > one vm is transmitting data to another, while both use different pci functions of > the same port of the same nic. > > In case there is a promiscuous client in the rx (which wants to receive all > data) or if the traffic is broadcast, traffic may be sent on both the loopback > channel and the physical wire. > > The reason tx-switching is controlled by a module parameter is twofold: > 1. There is a certain performance penalty for tx-switching because: > a. every packet must be compared against the receiver clients. > b. duplicated traffic being loopbacked can consume a significant portion of > the overall bandwidth, depending on the scenario. So you really want the driver/firmware/hardware to know all the local addresses (as John Fastabend was proposing). > 2. Tx-switching doesn't make much sense as a per function parameter, but should > rather be controlled uniformly for the entire device. [...] What if there are multiple such cards in the same system, and this is only wanted for one of them? Ben. -- Ben Hutchings, Staff Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.