From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Graf Subject: Re: [PATCH net] gso: do GSO for local skb with size bigger than MTU Date: Wed, 3 Dec 2014 23:05:51 +0000 Message-ID: <20141203230551.GC8822@casper.infradead.org> References: <20141202170927.GA9457@casper.infradead.org> <20141202173401.GB4126@redhat.com> <20141202174158.GB9457@casper.infradead.org> <20141203090339.GA9299@redhat.com> <20141203183859.GB16447@redhat.com> <20141203220244.GA8822@casper.infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Michael S. Tsirkin" , "Du, Fan" , Jason Wang , "netdev@vger.kernel.org" , "davem@davemloft.net" , "fw@strlen.de" , "dev@openvswitch.org" , Pravin Shelar To: Jesse Gross Return-path: Received: from casper.infradead.org ([85.118.1.10]:46461 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751309AbaLCXFz (ORCPT ); Wed, 3 Dec 2014 18:05:55 -0500 Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On 12/03/14 at 02:51pm, Jesse Gross wrote: > My proposal would be something like this: > * For L2, reduce the VM MTU to the lowest common denominator on the segment. > * For L3, use path MTU discovery or fragment inner packet (i.e. > normal routing behavior). > * As a last resort (such as if using an old version of virtio in the > guest), fragment the tunnel packet. That's what I had in mind as well although using a differentiator bit which indicates to the output path whether the packet is to be considered switched or routed and thus send ICMPs. The bit would be set per flow, thus allowing arbitary granularity of behaviour. I haven't fully thought this through yet though.