[openib-general] is wc valid if ib_poll_cq() returns zero

[somenath]

Rimmer, Todd wrote:

>>From: Sean Hefty
>>somenath wrote:
>>    
>>
>>>2. why is the io completion routine called when ib_poll_cq() returns
>>>zero? does this kind of notification contain any information?
>>>is there some error happening here? what are some possible problem
>>>      
>>>
>>areas?
>>    
>>
>>>any wild guess...?
>>>      
>>>
>>Can you clarify what's happening?  Are you calling ib_poll_cq() from
>>    
>>
>your
>  
>
>>ib_comp_handler() and not finding a completion?
>>    
>>
>
>Be aware that an IB completion handler should be coded as:
>
>while poll_cq returns a completion
>	process completion
>rearm CQ
>  
>

that's what I am doing, to be more specific:

rearm CQ;
while (ib_poll_cq(cq, 1, &wc) > 0) {
     process completion();
}

is that what you meant?

>while poll_cq returns a completion
>	process completion
>
>Per the IBTA spec, rearm CQ is not required to generate an event for
>completions already on the CQ, just for newly arriving ones (Mellanox
>HCAs will generate a completion event if any CQEs remain on the CQ).
>
>Due to various race situations between the HCA and the software/ULP,
>there are some valid cases where a completion event could occur after
>poll_cq has already processed the completion.
>  
>

in my case, poll_cq() always returns 0, so I never get a valid wc entry...

>Todd Rimmer
>  
>