If we have not drained the CQ (consumed budget or more) the second
condition (ib_req_notify_cq) will not be invoked. We are only rearming
the CQ when we drained it completely. So I don't see how we can end up
with missed notifications.
We drain the CQ completely for whatever CQEs available at that time,
say for example,
33 CQEs drained at time t1. So now req_notify_cq will be invoked at time t2.
During time delta t2-t1, CQ in hardware remains unarmed.
If cqes are added during that time delta, Will event/interrupt raised
for it, for CQ in unarmed state?
At time time t2, CQ is armed containing pending CQEs. Will
event/interrupt raised for those pending CQEs on next arming?
If the device did not reported missed-events then it is the device
responsibility to generate a new completion event after arming.
Specifically, the mlx4/mlx5 HW is able to generate a completion event
in your described scenario. A device that is not capable of doing so
must report missed events to inform the core it has more completions
to consume.
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