[openib-general] Immediate data question

[Dotan Barak]

Hi CQ.

Tang, Changqing wrote:
> Roland:
> 	If I only want to send/recv 4 bytes with immediate data:
>
> On sender side:
> 	opcode = IBV_WR_SEND_WITH_IMM;
> 	imm_data = my_4_bytes_data;
>
> 	Do I still need to specify sg_list and num_sge ?
>   
If the data that is being sent is only the immediate data, so no MR 
should be registered in this side.
The SR will look like this:
sr.opcode = IBV_WR_SEND_WITH_IMM;
sr.imm_data = my_4_bytes_data;
sr.num_sge = 0;
> On receiver side, because the immediate data is inside the completion
> structure, do I need to post a receive for above message ?
> If I need to post a receive, do I need to specify sg_list and num_sge
> for the receive ?
>   
In the receiver side you must post RR (because SEND opcode consumes a RR).

If you are using UD QP, you must add s/g list with 40 bytes (of 
registered memory).
If you are not using UD QP, the s/g list in this side can be empty 
(num_sge = 0) and the data that was sent will be
provided to you in wc.imm_data.
> I looked the spec but did not find useful information.
>
> The reason I ask is that at some point, I can not(or hard) to provide
> registered memory only for 4 bytes data.
>   
I think that you can avoid registering those 4 bytes ...


Hope this helped you
Dotan