Re: [dpdk-stable] [dpdk-dev] [PATCH 0/2] virtio fix false offload claims

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 23 Aug 2017 18:14:44 +0200
Olivier MATZ <olivier.matz@6wind.com> wrote:

> On Wed, Aug 23, 2017 at 08:31:35AM -0700, Stephen Hemminger wrote:
> > On Wed, 23 Aug 2017 11:30:26 +0200
> > Olivier MATZ <olivier.matz@6wind.com> wrote:
> >   
> > > Hello,
> > > 
> > > On Sat, Jul 08, 2017 at 11:12:22AM +0800, Yuanhan Liu wrote:  
> > > > On Fri, Jul 07, 2017 at 12:52:48PM -0700, Stephen Hemminger wrote:    
> > > > > While doing code for Hyper-V, noticed that the virtio driver was
> > > > > confused about receive versus transmit offloads.  The virtio
> > > > > checksum offload is L4 (TCP/UDP) only, not IPv4. Also, TSO
> > > > > and LRO are not the same.
> > > > > 
> > > > > This may break some program that was assuming it was getting offloads
> > > > > that it wasn't.    
> > > > 
> > > > Applied to dpdk-next-virtio.
> > > > 
> > > > And I think they should be backported to stable releases, thus,
> > > > 
> > > >     Cc: stable@dpdk.org
> > > > 
> > > > Thanks.
> > > > 
> > > > 	--yliu    
> > > > > 
> > > > > Stephen Hemminger (2):
> > > > >   virtio: don't falsely claim to do IP checksum
> > > > >   virtio: don't claim to support LRO
> > > > > 
> > > > >  drivers/net/virtio/virtio_ethdev.c | 30 +++++-------------------------
> > > > >  1 file changed, 5 insertions(+), 25 deletions(-)
> > > > > 
> > > > > -- 
> > > > > 2.11.0    
> > > 
> > > I think these 2 commits break the virtio offload, which can be tested as
> > > described in this test plan:
> > > http://dpdk.org/ml/archives/dev/2016-October/048092.html
> > > 
> > > First, about checksum: the description of rxmode->hw_ip_checksum is:
> > > 
> > >      hw_ip_checksum   : 1, /**< IP/UDP/TCP checksum offload enable. */
> > > 
> > > So, while I agree the name is not well chosen, it is valid to set it
> > > for virtio to enable L4 checksum.
> > > 
> > > Then about LRO: setting rxmode->enable_lro is a way to tell the host that the
> > > guest is ok to receive tso packets. From the guest point of view, it is like
> > > enabling lro on a physical driver. Again, it is valid and useful to do this.
> > > 
> > > Before removing these features, it would have been nice to have a quick look at
> > > the commits that introduced them.  
> > 
> > I am ok with keeping LRO as long as the documentation changed.  And virtio
> > driver did some enforcement. 
> > 
> > For checksums, the hw_ip_checksum flag either needs to be more fine grain (IP, UDP, TCP)
> > which would be best, or virtio would have to check IP checksum in software.
> >   
> 
> For checksum, yes, the rxconf should be more fine-grained and renamed.
> 
> But apart from the name which is confusing, it was not wrong.
> Setting hw_ip_checksum=1 means: "allow the driver to return packets with
> checksums flags != unknown". These flags are good,bad,unknown,none for
> both l3 and l4. So virtio driver always return unknown for l3, and
> none|unknown|good|bad for l4, depending on what the host passed.

You are right, I forgot that there now is way to indicate unknown
for checksums. Before that it was limited good/bad.

Let's revert both these patches, and update the documentation?