[Rdma-developers] Re: [openib-general] OpenIB and OpenRDMA: Convergence on common RDMA APIs and ULPs for Linux

[Sukanta ganguly]

I agree.

SG
--- Bernard Metzler <BMT at zurich.ibm.com> wrote:

> Sukanta,
> 
> without touching any TOE issues (this question is
> about RDMA, right?), 
> after
> transforming a TCP connection into RDMA mode and
> using an RDMA API,
> the socket file descriptor is not longer to be used
> for communication.
> In fact, on some implementations the stream socket
> resources will
> even get released. That is, if the socket was the
> direct consumer
> of the TCP stream, then now it is RDMAP/DDP/MPA.
> RDMA APIs such as IT-API defining a specific call to
> convert a socket 
> based
> connection into RDMA mode (e.g.,
> it_socket_convert()).
> Other consumers may directly start via an RDMA API,
> never
> opening a consumer controlled socket.
> 
> So, in RDMA mode, communication will happen via the
> RDMA API. At this
> stage, the kernel still have to keep completely in
> its hands the
> synchronisation of state information related to that
> offloaded
> connection(s) with the host stack (it would have to
> protect the
> local port used by the offloaded connection for
> example, others
> are routing, ARP, SNMP...), but it is not involved
> at the data path.
> 
> With respect to the kernel based TCP stack, what is
> not needed is
> a hack into the stack and scatter/gather state
> information of the live
> TCP connection between kernel and RNIC, but to find
> one clean interface
> to transfer state information out of that stack and
> to the RNIC.
> 
> 
> With limited benefit, one could of course also
> implement native 
> sockets over RDMA, where an in-kernel midlayer on
> top of kernel
> RDMA Verbs is doing the translation between send(),
> receive() to 
> post_send, post_receive. But usage of 'true RDMA'
> operations
> like RDMA READ or WRITE might be limited, and I
> don't see much value 
> for the user here. One variety of this approach with
> less limited
> access to RMDA benefits might be sockets with
> extended RDMA 
> semantics.
> 
> Bernard.
> 
> rdma-developers-admin at lists.sourceforge.net wrote on
> 27.05.2005 15:40:43:
> 
> > Venkata,
> >    How will that work? If the RNIC offloads RDMA
> and
> > TCP completely from the Operating System and does
> not
> > share any state information then the application
> > running on the host will never be in the position
> to
> > utilize the socket interface to use the
> communication
> > logic to send and receive data between the remote
> node
> > and itself. Some information needs to be shared.
> How
> > much of it and what exactly needs to be shared is
> the
> > question.
> > 
> > Thanks
> > SG
> > 
> > --- Venkata Jagana <jagana at us.ibm.com> wrote:
> > > 
> > > 
> > > 
> > > 
> > > 
> > > 
> > > rdma-developers-admin at lists.sourceforge.net
> wrote on
> > > 05/25/2005 09:47:00
> > > PM:
> > > 
> > > > Venkata,
> > > > Interesting coincidence: I was talking with
> > > someone (at HP) today
> > > > who knows substantially more than I do about
> > > RNICs.
> > > > They indicated RNICs need to manage TCP state
> on
> > > the card from userspace.
> > > > I suspect that's only possible through a
> private
> > > interface
> > > > (e.g. ioctl() or /proc) or the non-existant
> (in
> > > kernel.org)
> > > > TOE implementation. Is this correct?
> > > >
> > > 
> > > Not correct.
> > > 
> > > Since RNICs are offloaded adapters with RDMA
> > > protocols layered on
> > > top of TCP stack, they do maintain the TCP state
> > > internally but
> > > it does not expose to the host. RNIC expose only
> > > RNIC Verbs interface
> > > to the host bot not TOE interface.
> > > 
> > > Thanks
> > > Venkat
> > > 
> > > >
> > > > hth,
> > > > grant
> > > >
> > > >
> > > >
> > >
> >
>
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