[Beowulf] Slection from processor choices; Requesting Giudence

Douglas Eadline deadline at clustermonkey.net
Fri Jun 16 20:11:13 EDT 2006


>
>> - The network/MPI combination is fairly critical to good performance and
>> to
>> price/performance. I have done some benchmarks where the right MPI
>> library
>> on GigE produces faster results than a bad MPI library on Myrinet. Seems
>> counter-intuitive, but I've seen it.
>> Jeff
>
> Jeff, we know how some people can mess up installs, but if you have
> gigabit
> Ethernet,
> with a one way pingpong latency of like 50-100 us if you're lucky,

Luck has very little to do with it. It is not uncommon with
properly tuned GigE adapters to get 28-32 us TCP latency
(measured with netpipe) However, low latency may not provide better
performance in all cases. You can do better than this of course
(11 us MPI latency for GigE):

http://www.clustermonkey.net//content/view/121/33/1/1/

I have found the Intel NICs to work the best. Tuning the interrupt
strategy is important.

 --
 Doug


> which
> is
> not using DMA i
> guess by default; in short nonstop interrupting your cpu,
> versus newer myri cards that are probably under 3 us, factor 20 to 30
> advantage to
> myri then you need to really not manage to install the network to let
> gigabit ethernet work better.
>
> That said it's not easy of course to install the network, but let's not
> assume that someone who
> builds a cluster doesn't manage to install the hardware he gets.
>
> For that huge amount of money from the highend manufacturers that you pay
> for their hardware, you
> DO get great support if you really don't manage to install it.
>
> There is not really exceptions to that.
>
> Vincent
>
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-- 
Doug
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