From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sasha Levin Subject: Re: [PATCH] kvm tools: virtio-net mergable rx buffers Date: Sun, 28 Apr 2013 22:36:41 -0400 Message-ID: <517DDCB9.1070708@oracle.com> References: <1366677147-2150-1-git-send-email-sasha.levin@oracle.com> <51774894.7080008@oracle.com> <20130424092328.GC11245@redhat.com> <87bo8ydv3b.fsf@rustcorp.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "Michael S. Tsirkin" , Pekka Enberg , Eric Northup , Will Deacon , Marc Zyngier , KVM , Asias He , jasowang@redhat.com To: Rusty Russell Return-path: Received: from userp1040.oracle.com ([156.151.31.81]:49629 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756835Ab3D2Chl (ORCPT ); Sun, 28 Apr 2013 22:37:41 -0400 In-Reply-To: <87bo8ydv3b.fsf@rustcorp.com.au> Sender: kvm-owner@vger.kernel.org List-ID: On 04/28/2013 08:44 PM, Rusty Russell wrote: > "Michael S. Tsirkin" writes: >> > On Wed, Apr 24, 2013 at 09:51:57AM +0300, Pekka Enberg wrote: >>> >> Hi, >>> >> >>> >> On 04/23/2013 12:35 PM, Eric Northup wrote: >>>>> >> >> Do you care about guests with drivers that don't negotiate >>>>> >> >> VIRTIO_NET_F_MRG_RXBUF? >>> >> >>> >> On Wed, Apr 24, 2013 at 5:51 AM, Sasha Levin wrote: >>>> >> > We usually try to keep backward compatibility, but in this case >>>> >> > mergable RX buffers are about 5 years old now, so it's safe to >>>> >> > assume they'll be running in any guest. >>>> >> > >>>> >> > Unless there is a specific reason to allow working without them >>>> >> > I'd rather keep the code simple in this case. >>> >> >>> >> Are there such guests around? What's the failure scenario for them >>> >> after this patch? >>> >> >>> >> Pekka >> > >> > Warning: have not looked at the patch, just a general comment. >> > >> > I think it's reasonable to assume embedded guests such as PXE won't >> > negotiate any features. And, running old guests is one of the reasons >> > people use virtualization at all. So 5 years is not a lot. >> > >> > In any case, stick to the device spec please, if you want it changed >> > please send a spec patch, don't deviate from it randomly. > Supporting old guests is an quality of implementation issue. It's like > any ABI: if noone will notice, you can remove stuff. > > But the case of "I can receive GSO packets but I don't support mergeable > buffers" is a trivial one: you can "support" it by pretending the guest > can't handle GSO :) > > If you want to support non-Linux guests (eg. bootloaders), you probably > want to keep support for very dumb drivers with no mergable rxbufs > though. Yup, I'm planning on sending a version that supports older guests soonish. Thanks, Sasha