Re: [RFC v2] RoCE v2.0 Entropy - IPv6 Flow Label and UDP Source Port

[Jason Gunthorpe <jgg@ziepe.ca>]

On Thu, Feb 06, 2020 at 09:18:38AM -0500, Tom Talpey wrote:
> On 1/8/2020 9:26 AM, Alex Rosenbaum wrote:
> > A combination of the flow_label field in the IPv6 header and UDP source port
> > field in RoCE v2.0 are used to identify a group of packets that must be
> > delivered in order by the network, end-to-end.
> > These fields are used to create entropy for network routers (ECMP), load
> > balancers and 802.3ad link aggregation switching that are not aware of RoCE IB
> > headers.
> > 
> > The flow_label field is defined by a 20 bit hash value. CM based connections
> > will use a hash function definition based on the service type (QP Type) and
> > Service ID (SID). Where CM services are not used, the 20 bit hash will be
> > according to the source and destination QPN values.
> > Drivers will derive the RoCE v2.0 UDP src_port from the flow_label result.
> > 
> > UDP source port selection must adhere IANA port allocation ranges. Thus we will
> > be using IANA recommendation for Ephemeral port range of: 49152-65535, or in
> > hex: 0xC000-0xFFFF.
> > 
> > The below calculations take into account the importance of producing a symmetric
> > hash result so we can support symmetric hash calculation of network elements.
> > 
> > Hash Calculation for RDMA IP CM Service
> > =======================================
> > For RDMA IP CM Services, based on QP1 iMAD usage and connected RC QPs using the
> > RDMA IP CM Service ID, the flow label will be calculated according to IBTA CM
> > REQ private data info and Service ID.
> > 
> > Flow label hash function calculations definition will be defined as:
> > Extract the following fields from the CM IP REQ:
> >    CM_REQ.ServiceID.DstPort [2 Bytes]
> >    CM_REQ.PrivateData.SrcPort [2 Bytes]
> >    u32 hash = DstPort * SrcPort;
> >    hash ^= (hash >> 16);
> >    hash ^= (hash >> 8);
> >    AH_ATTR.GRH.flow_label = hash AND IB_GRH_FLOWLABEL_MASK;
> > 
> >    #define IB_GRH_FLOWLABEL_MASK  0x000FFFFF
> 
> Sorry it took me a while to respond to this, and thanks for looking
> into it since my comments on the previous proposal. I have a concern
> with an aspect of this one.
> 
> The RoCEv2 destination port is a fixed value, 4791. Therefore the
> term

I read the above as using the destination port of the IP contained
within the CM REQ, not as the destination port of the RoCE UDP header?

So it can be different..

Jason