From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: Re: GSO / TSO offload dependency Date: Sun, 28 Feb 2010 19:30:46 +0000 Message-ID: <1267385446.2282.119.camel@localhost> References: Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: raj ravi Return-path: Received: from exchange.solarflare.com ([216.237.3.220]:52592 "EHLO exchange.solarflare.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S936463Ab0B1Tax (ORCPT ); Sun, 28 Feb 2010 14:30:53 -0500 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Sun, 2010-02-28 at 22:30 +0530, raj ravi wrote: > Hi, > I m currently working on TSO feature in Linux network driver. > > Please correct my understanding. > > GSO - Generic segmentation offload - does not require any hardware support. > > TSO - TCP segmentation offload - does require hardward support > > > Does TSO needs GSO to be turned on? OR in other words, can I have > GSO disabled and TSO Enabled ? > I beleive the code is tied between both offload...but not sure about > the above possibility... please clarify. Segmentation/fragmentation can be done in one of three places: 1. By the transport protocol, when constructing skbs to be queued 2. By the transport protocol, when an skb is about to be passed to the device (enabled by NETIF_F_GSO) 3. By the device driver and hardware (enabled by NETIF_F_TSO, NETIF_F_UFO, etc.) Depending on the context, 'GSO' can refer either to case 2, or to both cases 2 and 3. TSO does not need the NETIF_F_GSO feature to be turned on, but in some contexts it is considered to be included in GSO. > Just before handing over the packets to the Network driver, > segmentation is carried out a call to dev_gso_segment ( ) function. > Given GSO is enabled, It will take care about creating TCP and other > protocol segments too, even if TSO is disabled.. ..correct ? Correct. > If hardware supports TSO, and If TSO and GSO are both enabled, ... > what will happen to segmentation assembly by means of GSO ... > GSO will not do any segmentatoin assembly for TCP alone and will do > for other protocols ?? bit confused here? Please clarify. Your understanding is correct. 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.