XRC and ib_poll_cq

XRC and ib_poll_cq

[Shlomo Pongratz]

Hi

 From the XRC annex I understand that WQE is obtained by polling the CQ 
attached to the XRC SRQ.
Now in "struct ib_wc" we have a pointer of type "struct ib_qp *", should 
the pointer be cast to "struct ib_srq *"?
In short how do one gets the qp_context/srq_context?

S.P.

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RE: XRC and ib_poll_cq

[Hefty, Sean]

>  From the XRC annex I understand that WQE is obtained by polling the CQ
> attached to the XRC SRQ.
> Now in "struct ib_wc" we have a pointer of type "struct ib_qp *", should
> the pointer be cast to "struct ib_srq *"?
> In short how do one gets the qp_context/srq_context?

qp_context is accessible directly from struct ib_qp.  srq_context is available from struct ib_srq, the latter of which is also in struct ib_qp.
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RE: XRC and ib_poll_cq

[Shlomo Pongratz]

Hi Sean,

Thanks, it seems that I asked the question in a wrong way.
The context is what I need eventually but in order to find it I first 
need to recover the QP or the XRC SRQ.
Per core there may be several QP and SRQ using the same CQ.
When doing ib_poll_cq on the CQ the WQE in hand has only an ib_qp pointer.

S.P.

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RE: XRC and ib_poll_cq

[Hefty, Sean]

> Thanks, it seems that I asked the question in a wrong way.
> The context is what I need eventually but in order to find it I first
> need to recover the QP or the XRC SRQ.
> Per core there may be several QP and SRQ using the same CQ.
> When doing ib_poll_cq on the CQ the WQE in hand has only an ib_qp pointer.

Correct - dereference the qp pointer to get the context, srq, and srq_context.

struct ib_wc wc;

ib_poll_cq(...&wc)
my_qp = wc.qp;
my_qp_context = wc.qp->qp_context;
my_srq = wc.qp->srq;
my_srq_context = wc.qp->srq->srq_context;

this tells you what QP/SRQ the completion is related to.
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Re: XRC and ib_poll_cq

[Shlomo Pongratz]

On 4/3/2013 3:35 AM, Hefty, Sean wrote:
>> Thanks, it seems that I asked the question in a wrong way.
>> The context is what I need eventually but in order to find it I first
>> need to recover the QP or the XRC SRQ.
>> Per core there may be several QP and SRQ using the same CQ.
>> When doing ib_poll_cq on the CQ the WQE in hand has only an ib_qp pointer.
> Correct - dereference the qp pointer to get the context, srq, and srq_context.
>
> struct ib_wc wc;
>
> ib_poll_cq(...&wc)
> my_qp = wc.qp;
> my_qp_context = wc.qp->qp_context;
> my_srq = wc.qp->srq;
> my_srq_context = wc.qp->srq->srq_context;
>
> this tells you what QP/SRQ the completion is related to.
Hi Sean,

Your answer actually raises another question.
According to the annex the XRC SRQ is used directly (it is like an RD QP 
but without a requester side), and also in the user space example 
"xrc_pingpong.c" no QP is created on-top of the XRC SRQ.
So the question is what is this QP that you de-referenced in the 
statement "my_srq = wc.qp->srq;"?
Is it just and artifact of the implementation?

S.P.

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