Philip Frey1 wrote:
Hello,
what is the correct way to get completions from the CQ without missing
any?
I am currently using two separate CQs for the SQ and for the RQ.
In pseudocode I do about the following to wait for a completion:
ibv_get_cq_event(channel, &dst_cq, &ctx); //blocking wait for
CQ event
<-- EVENT -->
ibv_req_notify_cq(dst_cq, 0); // request event
for next completion
ibv_poll_cq(dest_cq, 1, wc); // get the WC from
the CQ
ibv_ack_cq_events(dst_cq, 1); // ack the event
It might now happen on the RQ, that two consecutive inbound sends consume
receive WRs and therefore generate two WCs on the RQ. If the second is
generated
before I get the first one, I will miss it and wait infinitely long
for it since I already got the event
but that event does not tell me how many WCs are pending on the
respective CQ.
One way to handle this issue would be to do an ibv_poll_cq() before
waiting for the event
in case there is something on the CQ for which I missed the event.
Is there a more elegant way to get all events pending on the CQ or
find out how many
completions are pending? I could also do a ibv_poll_cq() and request
say 10 completions
and see how many I got but that is kind of a hack...
you need to poll the cq until it is empty instead of just polling once.
get_cq_event()
req_notify_cq()
do {
ne = poll_cq();
} while (ne != 0);
ack_cq_event()
Steve.
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