Hi again,
Today I was trying with another TCP benchmark included in the hpcbench
suite, and with a ping-pong test I'm also getting 100us of latency. Then, I
tried with netperf and the same result....
So, in summary, I'm measuring TCP latency with messages size between 1-32
bytes:
Netperf over TCP -> 100us
Netpipe over TCP (NPtcp) -> 100us
HPCbench over TCP -> 100us
Netpipe over OpenMPI (NPmpi) -> 60us
HPCBench over OpenMPI -> 60us
Any clues?
Thanks a lot!
2012/1/10 Roberto Rey <eros.83_at_[hidden]>
> Hi,
>
> I'm running some tests on EC2 cluster instances with 10 Gigabit Ethernet
> hardware and I'm getting strange latency results with Netpipe and OpenMPI.
>
> If I run Netpipe over OpenMPI (NPmpi) I get a network latency around 60
> microseconds for small messages (less than 2kbytes). However, when I run
> Netpipe over TCP (NPtcp) I always get around 100 microseconds. For bigger
> messages everything seems to be OK.
>
> I'm using the BTL TCP in OpenMPI, so I can't understand why OpenMPI
> outperforms raw TCP performance for small messages (40us of difference). I
> also have run the PingPong test from the Intel Media Benchmarks and the
> latency results for OpenMPI are very similar (60us) to those obtained with
> NPmpi
>
> Can OpenMPI outperform Netpipe over TCP? Why? Is OpenMPI doing any
> optimization in BTL TCP?
>
> The results for OpenMPI aren't so good but we must take into account the
> network virtualization overhead under Xen
>
> Thanks for your reply
>
--
Roberto Rey Expósito
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