[ofa-general] [PATCH 1/4] ib/ipoib: specify TClassand FlowLabelwith PR queries for QoS support

[Jason Gunthorpe]

On Tue, Aug 07, 2007 at 10:43:22AM -0700, Sean Hefty wrote:
> >Rate and MTU should probably be copied over. Not sure about flowlabel
> >though..
> 
> Can you provide more details on your thinking for rate, mtu, and flowlabel?

Well, upon more though, I think rate can probably be dropped from the
list. The broadcast group rate should be the minimum rate that any
pair of ports can support in the IPoIB group, but that doesn't mean
all connections should be limited to that rate.

MTU - at a minimum the PR must request a MTU >= than the interface
MTU, having a MTU that is exactly equal to the broadcast group MTU
seems fine to me. The SM should be able to do >= internally.

Flowlabel - IBA hasn't really specified what to do with this field. In
IPv6 FlowLabel is assigned randomly by the host on a per-flow (ie
socket) basis to allow routers to group packets into flows without
doing deeper inspection. This becomes important when encryption is
used and the routers can no longer access the TCP header to find
flows. 

Also, my previous arguments on this list about routing and PR
suggested using FlowLabel as a way to disambiguate multipath in a
routed network. If that view is taken up then FlowLabel is purely an
output from the SM in all cases and should not be an input - much like
SL.

Jason