Re: TCP RDMA option to accelerate NFS, CIFS, SCSI, etc.

[Kacheong Poon <Kacheong.Poon@eng.sun.com>]

> The performance impact of RDMA is quite a bit larger than SACK, so
> I don't know that your example is relevant.  All the big vendors
> implement zero-copy in some shape or form and since RDMA is a scheme
> to make zero-copy work in more cases, I'm sure it will be picked up
> if the proposal is deemed sane.

Can you elaborate on this?  Suppose TCP "blindly" does zero copy everything to
an app's buffer (for example, to a web browser's receive buffer) without
RDMA.  Then the browser app looks at the data and displays it.  What is the
difference RDMA makes in this case?  Yes, RDMA can separate different messages
in the buffer.  But this can also be done by the browser app, not by TCP.

I guess this is what I suggest the authors to add to the draft.  It is not
clear to me how RDMA can make a difference, especially in those cases the
authors claim a big performance difference.

							K. Poon.
							kcpoon@eng.sun.com