[openib-general] IPOIB NAPI

[Shirley Ma]

oland Dreier <rdreier at cisco.com> wrote on 02/27/2007 02:41:44 PM:

>  > So the IBV_CQ_REPORT_MISSED_EVENTS has been part of OFED-1.2 already?
I can
>  > generate the patch for all ULPs to use this for review. Do you need me
to
>  > do that?
>
> No, it's not in OFED 1.2 or the upstream kernel.  And no one has
> implemented it for userspace (and I'm somewhat reluctant to break the
> ABI at this point without some performance numbers to motivate making
> this API change).
>
> Have the NAPI performance problems with ehca been resolved?  We could
> probably merge IPoIB NAPI for 2.6.22 then, which would pull in the
> kernel changes at least.
>
>  - R.
We have addressed the NAPI performance issues with ehca driver. I believe
the patches have been upper stream. However the test results show that it's
better to delay poll again to next NAPI interval, something like this:

poll-cq
notify-cq, if missed_event && netif_rx_reschedule()
return 1

vs.
poll-cq,
notify-cq, if missed_event && netif_rx_reschedule()
poll again
return 0

It seems ehca delivering packet much faster than other HCAs. So poll again
would stay in the loop for many many times. So the above changes doesn't
impact other HCAs, I would recommand it. I saw same implementations on
other ethernet drivers.

Thanks
Shirley Ma
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