Re: [storm] DDP messages ordering

Hello Tom,

Section 5.5 just specifies ordering rules of RDMAP requester and responder.
According to such rules RDMAP generates RDMA messages and passes them to DDP layer one by one for future processing.
RDMAP's granularity and visibility is a particular RDMA message.
DDP layer gets RDMA messages from RDMAP layer maps them one-by-one to DDP messages performs segmentation and passed them to transport layer.
So DDP segments interleaving/rules cannot be part of RDMAP , it is clearly DDP layer behavior.
And according to RFC 5041 Section 5.3 and already mentioned by you "first rule" cannot interleave DDP segments of different operations.

Best regards,
Lena

-----Original Message-----
From: Tom Talpey [mailto:tom@talpey.com]
Sent: Wednesday, September 09, 2015 6:54 PM
To: Elena Gurevich; storm@ietf.org
Subject: Re: [storm] DDP messages ordering

On 9/9/2015 9:07 AM, Elena Gurevich wrote:
> Hello,
>
> During my testing of some iWARP adaptor I discovered that RNIC interleaves DDP segments of Send and Read Response messages.
> According to your previous response this behavior is forbidden, is it ?

Not necessarily, because an RDMA Read response is special. It's injected into the DDP stream within the RNIC by RDMAP, and therefore it follows the RDMAP rules. See section 5.5 of RFC5040.

Tom.

>
> Best regards,
> Lena
>
> -----Original Message-----
> From: storm [mailto:storm-bounces@ietf.org] On Behalf Of Tom Talpey
> Sent: Tuesday, September 08, 2015 5:15 PM
> To: storm@ietf.org
> Subject: Re: [storm] DDP messages ordering
>
> On 9/8/2015 6:02 AM, Elena Gurevich wrote:
>> Hello,
>>
>> RFC 5041 section 5.3 stands that
>>
>> ----------------------------------
>>
>> 5.3 Ordering Among DDP Messages
>>
>> Messages passed through the DDP MUST conform to the ordering rules
>>
>> defined in this section.
>>
>> At the Data Source, DDP:
>>
>> * MUST transmit DDP Messages in the order they were submitted to
>>
>> the DDP layer,
>>
>> * SHOULD transmit DDP Segments within a DDP Message in increasing
>>
>> MO order for Untagged DDP Messages, and in increasing TO order
>>
>> for Tagged DDP Messages.
>>
>> ----------------------------------
>>
>> Does this mean that transmitter MUST not interleave DDM segments
>> related to consequent DDP messages ?
>
> It depends on what you mean by "the transmitter". It's certainly possible that network delivery and TCP retransmission can reorder segments. But the first rule requires that DDP not interleave two separate operations when passing them to the TCP transport.
>
> Tom.
>
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