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

[Michael S. Tsirkin]

Quoting r. Shirley Ma <xma at us.ibm.com>:
> Subject: Re: [PATCH/RFC 1/2] IB: Return "maybe_missed_event" hint from ib_req_notify_cq()
> 
> Roland Dreier <rdreier at cisco.com> wrote on 10/18/2006 01:55:13 PM:
> > I would like to understand why there's a throughput difference with
> > scaling turned off, since the NAPI code doesn't change the interrupt
> > handling all that much, and should lower the CPU usage if anything.
>
> That's I am trying to understand now.
> Yes, the send side rate dropped significant, cpu usage lower as well.

I think its a TCP configuration issue in your setup.
With NAPI, we seem to be getting stable high results as reported previously by
Eli. Hope to complete testing and report next week.

Shirley, can you please post test setup and results? Some ideas:

Please note that you need to apply the NAPI patch on both send and recv side
in stream benchmark, otherwise one side will be a bottleneck.

Please also note that due to factors such as TCP window limits, TX on a single
socket is often stalled.  To really stress a connection and see benefit from
NAPI you should be running multiple socket streams in parallel: either just run
multiple instances of netperf/netserver, or use iperf with -P flag.

You also should look at the effect of increasing the send/recv socket buffer
size.

Finally, tuning RX/TX ring size should also be done differently:
you might be over-running your queues, so make them bigger for NAPI.

-- 
MST