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

[Michael Krause <krause@cup.hp.com>]

At 04:10 PM 2/24/00 -0800, David S. Miller wrote:
>    Date: Thu, 24 Feb 2000 17:09:51 -0700
>    From: "Justin T. Gibbs" <gibbs@freebsd.org>
>
>    In the case of a server response, RDMA benefits the client, not the
>    server, so I fail to see why your example is problematic.  Zero
>    copy send is not what this standard addresses.
>
>With client memory bus bandwidth in the multi-gigabyte per second
>range, who needs to avoid the single copy?  How much NFS and web
>surfing does one need to do before this is would really come into
>play?
>
>And the bus speeds will just be faster by the time something like
>this could be deployed widely.

It ain't free and there are plenty of reasons to avoid copying data since 
many applications do not always touch the data being moved.  Also, http and 
web traffic are probably not the best examples to illustrate the value of 
RDMA Read and Write operations.  Storage which was the context that started 
this effort certainly benefits from a combination of send for 
control  messages and RDMA for data movement - doesn't matter whether this 
in user-space / kernel-space, client or server.  Those buffers may be only 
used by the server to reflect a data set to a set of users without ever 
touching the buffers themselves.  Also, one could use this technology with 
storage devices to bypass the server and send data to one or more NICs for 
remote access - RDMA is still quite good for this type of operation and 
does not involve touching the data.

Mike