RE: [rddp] verb spec clarification

[pat_thaler at agilent.com]

I think Paul missed the context of the question. Not surprising because the question is a little confusing:
"Section 9.2.5.1 states that QPs have Inbound RDMA Read enable and
Inbound RDMA Write and inbound RDMA Read Response enable.
 
Does the inbound RDMA Read Response enable check apply to a
zero length read response?"

The sections Paul mentioned don't address this question.

There is no RDMA Read Response enable check. Verbs seems to lack any description of the effect of these enables.

RDMA Read Response enable is a feature of queue creation. Presumably if RDMA Read Response handling is not enabled, there will be no resources provided for initiating RDMA Reads, i.e. ORD will be zero. Attempting to initiate an RDMA Read will fail.

These enables are not described very much and they may seem redundant with setting IRD and ORD to zero. A modify QP can change IRD and ORD. Setting up the QP with Inbound RDMA Read Response enabled and ORD zero would allow a later attempt to modify the QP to increase ORD. My expectation is that when a QP was set up with Inbound RDMA Read Response disabled, the RNIC can assume that RDMA Read initiation will never be allowed and any attempt to allocate ORD depth could be failed. This is the way I think it should work, but the reaction of an RNIC to a Create QP with Inbound RDMA write and RDMA Read Response disabled and ORD non-zero or a Modify QP for non-zero ORD when this is disabled are not described.

It also isn't clear why Inbound RDMA Write and inbound RDMA Read response share a single enable. They require different resources since the RDMA Read Response requires ORD depth. They aren't always needed together. An iSCSI target will receive inbound RDMA Writes and will not receive RDMA Read responses. An iSCSI initiator has the reverse situation. 

Regards,
Pat

-----Original Message-----
From: rddp-bounces at ietf.org [mailto:rddp-bounces at ietf.org]On Behalf Of
Caitlin Bestler
Sent: Tuesday, 29 March, 2005 7:41 AM
To: Culley, Paul
Cc: Patricio Kaplan; rddp at ietf.org
Subject: Re: [rddp] verb spec clarification


Culley, Paul wrote:
> For Verbs, The answer is no.
> 
> Section 7.6.3 pg 112 near top
> "If the length of the access is zero, the RI MUST NOT perform any of the
> above checks on the Memory Region."
> 
> Section 7.10.6.2 pg 124, 2/3 down
> "If the length of the access is zero, the RI MUST NOT perform any of the
> above checks on the Memory Window."
> 

Additional point: checking IRD credits is a check on the connection(QP)
not on the Memory Region/Memory Window.

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