Re: [virtio-comment] Re: [virtio-dev] Re: [virtio-comment] [PATCH v13] virtio-net: support inner header hash

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, May 05, 2023 at 09:51:15PM +0800, Heng Qi wrote:
> On Thu, Apr 27, 2023 at 01:13:29PM -0400, Michael S. Tsirkin wrote:
> > On Thu, Apr 27, 2023 at 10:28:29AM +0800, Heng Qi wrote:
> > > 
> > > 
> > > å 2023/4/26 äå10:48, Michael S. Tsirkin åé:
> > > > On Wed, Apr 26, 2023 at 10:14:30PM +0800, Heng Qi wrote:
> > > > > This does not mean that every device needs to implement and support all of
> > > > > these, they can choose to support some protocols they want.
> > > > > 
> > > > > I add these because we have scale application scenarios for modern protocols
> > > > > VXLAN-GPE/GENEVE:
> > > > > 
> > > > > +\item In scenarios where the same flow passing through different tunnels is expected to be received in the same queue,
> > > > > +      warm caches, lessing locking, etc. are optimized to obtain receiving performance.
> > > > > 
> > > > > 
> > > > > Maybe the legacy GRE, VXLAN-GPE and GENEVE? But it has a little crossover.
> > > > > 
> > > > > Thanks.
> > > > But VXLAN-GPE/GENEVE can use source port for entropy.
> > > > 
> > > > 	It is recommended that the UDP source port number
> > > > 	 be calculated using a hash of fields from the inner packet
> > > > 
> > > > That is best because
> > > > it allows end to end control and is protocol agnostic.
> > > 
> > > Yes. I agree with this, I don't think we have an argument on this point
> > > right now.:)
> > > 
> > > For VXLAN-GPE/GENEVE or other modern tunneling protocols, we have to deal
> > > with
> > > scenarios where the same flow passes through different tunnels.
> > > 
> > > Having them hashed to the same rx queue, is hard to do via outer headers.
> > > > All that is missing is symmetric Toepliz and all is well?
> > > 
> > > The scenarios above or in the commit log also require inner headers.
> > 
> > Hmm I am not sure I get it 100%.
> > Could you show an example with inner header hash in the port #,
> > hash is symmetric, and you still have trouble?
> > 
> > 
> > It kinds of sounds like not enough entropy is not the problem
> > at this point.
> 
> Sorry for the late reply. :)
> 
> For modern tunneling protocols, yes.
> 
> > You now want to drop everything from the header
> > except the UDP source port. Is that a fair summary?
> > 
> 
> For example, for the same flow passing through different VXLAN tunnels,
> packets in this flow have the same inner header and different outer
> headers. Sometimes these packets of the flow need to be hashed to the
> same rxq, then we can use the inner header as the hash input.
> 
> Thanks!

So, they will have the same source port yes? Any way to use that
so we don't depend on a specific protocol?

-- 
MST