[dat-discussions] [openib-general] [RFC] DAT2.0immediatedataproposal

[Larsen, Roy K]

>> All we're asking is that a write/send combined API not be
>> called immediate data unless it fits the semantics of
>> immediate data.  I am puzzled at the resistance this is
>> getting.  There is a standards body specification for
>> immediate data.  If it is not followed, don't call it
>> immediate data.  It's that simple.  For those transports that
>> can provide the service, the UPL may be able to gain access to it
>> through an extension.
>>
>
>I have no objection to calling this
>"dat_ep_post_rdma_write_with_notifier"
>and labelling the 32-bit data as a "notifier tag".

If this MUST be implanted by the provider as a (possibly optimized)
write followed by a send, that sounds good to me.  All transports can
support it and provide the same semantic.  No need for application
schism.  However, I wouldn't place a restriction on the size of the
notifier tag.  Somewhere along the line, the send data has to reside in
a registered buffer.  Might as well have the ULP supply it and let it
define the contents and size.
 
>
>Even on iWARP transports small send data can be in-lined,
>avoiding the need for buffers to be registered. A special
>API where the length of the "send buffer" is known in
>advance makes this even easier.

Ah, I wasn't aware iWARP could carry inline data.  I take it that's not
possible on an iWARP RDMA write PDU however.

>
>What I still fail to see is a rationale that works down
>from the application layer on why an application would
>need still one more page in their cookbook. Creating an
>entire new method to enable a strange method of signalling
>one bit of information to the other end doesn't seem like
>much of a payoff to me.

Of course the semantics are much more that signaling one bit.
Nevertheless, if the contention is that applications don't need that
bit, that all they need are write/send semantics, then by all means,
simply define an API that gives them that and this thread is closed.
Provider writers for transports that can supply a true immediate data
service would be free to waste their time supplying an unused service
through an extension.  But that business decision should be left to the
provider writer, not his mailing list.

Roy