[Beowulf] MPI performance gain with jumbo frames

[Douglas Eadline]

So this begs the question, if we are "core rich and packet small"
do we care about packet size and overhead?  In other words if we have
plenty of cores when do we not care about communication
overhead. Most GigE drivers have various interrupt coalescence
strategies and of course Jumbo Frames to lessen the processor
load, but if we have multi-core do we need to care about this
as much ... any thoughts?

--
Doug


> Doug and Jeff have good points (and some good links).  On thing to
> also pay attention to is the CPU utilization during the bandwidth and
> application testing.  We found that on our cluster (various Dells
> with built in GigE NICs) while we did not see huge differences in
> effective bandwidth, the CPU overhead was notably less when using
> Jumbo Frames.
>
> Again, YMMV.
>
> Good luck,
>
> -bill
>
> On Jun 11, 2007, at 11:57 AM, Jeffrey B. Layton wrote:
>
>> Doug brings up some good points. If you want to try Jumbo
>> Frames to improve MPI performance you might have to
>> tweak the TCP buffers as well. There are some links around
>> the web on this. Sometimes it helps performance, sometimes
>> it doesn't. Your mileage may vary.
>>
>> Jeff
>
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--
Doug