[ofa-general] missed cq event

[Roland Dreier]

 > You know, I've never quite liked this fact.  I've seen multiple
 > people, including myself, get tripped up by this issue.  And now we
 > have lots of applications with code to:  determine the queue depth,
 > increment a counter on every send and periodically post a SIGNALED
 > one, and handle the uninteresting CQ event.
 > 
 > Trying not to think about how the hardware works for a moment, this
 > issue can be seen as yet another little detail that apps people must
 > learn to use RDMA devices.  Any ideas on how verbs could handle this
 > case itself?

I don't see a good way that this could be handled at the verbs level.
How does the app know when the resources associated with the send
request can be freed?  How would you size your CQ (given than any and
all unsignaled requests might generate a completion with error)?

What would you want to happen if an app posts 101 work requests to a
queue of depth 100 before any WRs complete?

It seems to me that the app needs the periodic completion just as much
as the hardware driver needs it for book-keeping.

 - R.