From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: Why is LRO off by default on ixgbe? Date: Wed, 23 Sep 2009 10:07:18 -0700 Message-ID: <20090923100718.79877040@s6510> References: <4ABA4D07.50107@candelatech.com> <20090923095356.7f9aef37@s6510> <4ABA538F.7020507@candelatech.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: NetDev To: Ben Greear Return-path: Received: from mail.vyatta.com ([76.74.103.46]:43940 "EHLO mail.vyatta.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751914AbZIWRH0 (ORCPT ); Wed, 23 Sep 2009 13:07:26 -0400 In-Reply-To: <4ABA538F.7020507@candelatech.com> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, 23 Sep 2009 09:57:51 -0700 Ben Greear wrote: > On 09/23/2009 09:53 AM, Stephen Hemminger wrote: > > On Wed, 23 Sep 2009 09:29:59 -0700 > > Ben Greear wrote: > > > >> I just noticed that enabling LRO on ixgbe lets me reach about 9Gbps receive on two > >> NICs concurrently in an NFS test, where I was only getting about 6Gbps w/out it (1500 MTU). > >> > >> Why is LRO disabled by default? > >> > >> Thanks, > >> Ben > > > > LRO is turned off if bridging or routing because of End to End requirements. > > That makes sense. > > If I know that all interfaces in question can handle TSO and LRO, > I could manually enable LRO w/out risk, right? > The problem is that LRO merges TCP packets, this breaks the end-to-end ack clocking and checksumming, and therefore is not enabled. That is why GRO is the replacement solution (preserves packet boundaries)