Re: [PATCH V1 for-next 1/2] IB/core: Report LSO capabilities when querying device

[Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>]

On Tue, May 10, 2016 at 07:29:42PM -0500, Christoph Lameter wrote:
> > > Exactly, this is why it is posted on the open mailing list where
> > > everyone has stage to express their opinion, including these mysterious
> > > hardware architecture who cares about future design, but doesn't care about
> > > its future support.
> >
> > Look, if you want linux-rdma to be setting hardware standards then get
> > a consensus from the vendors on this idea.
> 
> This is about exporting existing hardware features that are already
> available through the standard socket APIs.

Eh? How is LSO or RSS available through standard socket APIs? Yes, it
is indirectly through the TCP stack, but the actual hardware feature
is not directly accessible???

> > This was tried at the Collab summit and I heard several representatives
> > strongly say no.
> 
> Hardware standards? I thought we were talking about software and APIs.

The LSO, RSS and Timestamp patches all demand very specific hardware
functionality for a device to implement the API. It is fundamentally
not a 100% software API.

Look at the patches. The LSO patch is so bad Sean and Steve couldn't
even figure out what the heck the HW feature does. I know what it
does, but I can't tell you the fine details of the actual required
hardware behavior.

How on earth is someone else supposed to ever implement hardware that
does this?

I still don't understand why this is being forced into
libibverbs. dpdk would seem to be the prefered way to access these
sorts of features and there is no technical reason why the mlx
dpdk provider needs to use libibverbs. Talk directly to /dev/uverbs0
and use udata to enable the universe of nic specific features.

For instance, the dpdk community has already done the hard work to
figure out how to expose things like LSO to their users - and they
actually have multiple vendors providing these features...

http://dpdk.org/ml/archives/dev/2014-May/002537.html

I guess you are going to tell me you want these features on IB UD
transport and dpdk has no support for L2's other than ethernet?

Jason
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