[openib-general] [PATCH/RFC 1/2] IB: Return "maybe_missed_event" hint from ib_req_notify_cq()

[Roland Dreier]

 > What I have found in ehca driver, n! = t, does't mean it's empty. If poll
 > again, there are still some packets in cq. IB_CQ_REPORT_mISSED_EVENTS most
 > of the time reports 1. It relies on netif_rx_reschedule() returns 0 to exit
 > napi poll. That might be the reason in poll routine for a long time? I will
 > rerun my test to use n! = 0 to see any difference here.

Maybe there's an ehca bug in poll CQ?  If n != t then it should mean
that the CQ was indeed drained.  I would expect a missed event would
be rare, because it means a completion occurs between the last poll CQ
and the request notify, and that shouldn't be that common...

My rough estimate is that even at a higher throughput than what you're
seeing, IPoIB should only generate ~ 500K completions/sec, which means
the average delay between completions is 2 microseconds.  So I
wouldn't expect completions to hit the window between poll and request
notify that often.

 - R.