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

[Heng Qi <hengqi@linux.alibaba.com>]

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!