Re: New List: rdma@cisco.com: to discuss RDMA

["Randall R. Stewart" <randall@stewart.chicago.il.us>]

Douglas:

I may be missing something here, but sendmsg() and recvmsg() both
have scatter/gather arrays within the berkley sockets api.
I am not sure that one can uses sendmsg() recvmsg() with TCP.. I
have never tried. As far as SCTP goes, we have defined a sockets
mapping... the draft is released but real rough.. an next version
is in the works.... the current "rough" cut can be found at:

http://search.ietf.org/internet-drafts/draft-stewart-sctpsocket-sigtran-00.txt

Now it may be that I am missing a key point in this discussion.. were
you
thinking other than the iovec structure... or were you thinking a
modification
that allows the pages to be stolen with no copy... the no copy becomes
a implemenation issue.. I have done something like it in the past
where if the application gives a 4k page in the send, the O/S underneath
does a swap of a page from kernel space with the user space one...

But as I say, this is real implemenation dependant :)

R

Douglas Otis wrote:
> 
> Charles,
> 
> With respect to SCTP, features added by a TCP option for RDMA are not needed
> to support alignment and out of sequence processing that ultimately alters
> the TCP API.  SCTP adds these features without disruption or modification to
> TCP.  The intent of VI is to allow scatter/gather function to handled by the
> target.  A safer scheme would be to adhere to SCSI conventions and implement
> zero copy and out of sequence processing using SCTP and SAM structures
> related to locally pre-arranged transfer structures.  This would keep the
> initiator or client in intimate control of memory and not reliant on targets
> eliminating boundary checking.  Such a feature will slightly impact SCTP to
> add a means to generally encapsulate a data payload associated with
> structure of pointers equipped with scatter-gather lists and relative
> offsets.  Specifically, this could be defined as the FCP structure data
> structure in SCSI implementations.  I would whole-heartedly endorse such
> features within SCTP.  I would dissuade such features from being added to
> TCP.  One could view the scatter-gather list structure as a token to be used
> by the target in more conventional VI methods.
> 
> Doug
> 
> > -----Original Message-----
> > From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
> > Charles Monia
> > Sent: Wednesday, September 27, 2000 11:49 AM
> > To: csapuntz@cisco.com; Jim Williams
> > Cc: ips@ece.cmu.edu
> > Subject: RE: New List: rdma@cisco.com: to discuss RDMA
> >
> >
> >
> >
> > > -----Original Message-----
> > > From: csapuntz@cisco.com [mailto:csapuntz@cisco.com]
> > > Sent: Wednesday, September 27, 2000 10:16 AM
> > > To: Jim Williams
> > > Cc: ips@ece.cmu.edu; csapuntz@cisco.com
> > > Subject: Re: New List: rdma@cisco.com: to discuss RDMA
> > >
> > >
> > >
> > > Does anybody on the list object to specifying an RDMA mechanism for
> > > use with iSCSI? Does anybody on the list object to mandating an RDMA
> > > mechanism? Please include your reasons.
> > >
> >
> > I'd object to mandationg the use of RDMA in iSCSI. However, I
> > would support
> > structuring the spec so that an RDMA transport mechanism could be used
> > underneath (I guess that's motherhood). If the iSCSI folks decided this
> > wasn't a priority issue, that's ok with me too.
> >
> > Charles
> >

-- 
Randall R. Stewart
randall@stewart.chicago.il.us or rrs@cisco.com
815-342-5222 (cell) 815-477-2127 (work)