Open MPI logo

Open MPI User's Mailing List Archives

  |   Home   |   Support   |   FAQ   |   all Open MPI User's mailing list

Subject: Re: [OMPI users] Strange TCP latency results on Amazon EC2
From: teng ma (tma_at_[hidden])
Date: 2012-01-12 10:51:07


Is it possible your EC2 cluster has another "unknown" crappy Ethernet
card(e.g. 1Gb
Ethernet card) . For small messages, they go through different paths in
NPtcp or MPI over NPmpi.

Teng Ma

On Thu, Jan 12, 2012 at 10:28 AM, Roberto Rey <eros.83_at_[hidden]> wrote:

> Thanks for your reply!
>
> I'm using TCP BTL because I don't have any other option in Amazon with 10
> Gbit Ethernet.
>
> I also tried with MPICH2 1.4 and I got 60 microseconds...so I am very
> confused about it...
>
> Regarding hyperthreading and process binding settings...I am using only
> one MPI process in each node (2 nodes for a clasical ping-pong latency
> benchmark). I don't know how it could affect on this test...but I could try
> anything that anyone suggest to me
>
> 2012/1/12 Jeff Squyres <jsquyres_at_[hidden]>
>
>> Hi Roberto.
>>
>> We've had strange reports of performance from EC2 before; it's actually
>> been on my to-do list to go check this out in detail. I made contact with
>> the EC2 folks at Supercomputing late last year. They've hooked me up with
>> some credits on EC2 to go check out what's happening, but the pent-up email
>> deluge from the Christmas vacation and my travel to the MPI Forum this week
>> prevented me from testing yet.
>>
>> I hope to be able to get time to test Open MPI on EC2 next week and see
>> what's going on.
>>
>> It's very strange to me that Open MPI is getting *better* than raw TCP
>> performance. I don't have an immediate explanation for that -- if you're
>> using the TCP BTL, then OMPI should be using TCP sockets, just like netpipe
>> and the others.
>>
>> You *might* want to check hyperthreading and process binding settings in
>> all your tests.
>>
>>
>> On Jan 12, 2012, at 7:04 AM, Roberto Rey wrote:
>>
>> > 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
>> > _______________________________________________
>> > users mailing list
>> > users_at_[hidden]
>> > http://www.open-mpi.org/mailman/listinfo.cgi/users
>>
>>
>> --
>> Jeff Squyres
>> jsquyres_at_[hidden]
>> For corporate legal information go to:
>> http://www.cisco.com/web/about/doing_business/legal/cri/
>>
>>
>> _______________________________________________
>> users mailing list
>> users_at_[hidden]
>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>>
>
>
>
> --
> Roberto Rey Expósito
>
> _______________________________________________
> users mailing list
> users_at_[hidden]
> http://www.open-mpi.org/mailman/listinfo.cgi/users
>

-- 
| Teng Ma          Univ. of Tennessee |
| tma_at_[hidden]        Knoxville, TN |
| http://web.eecs.utk.edu/~tma/       |