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Subject: Re: [OMPI users] TCP Latency
From: Steve Wise (swise_at_[hidden])
Date: 2008-08-17 10:53:14


With OpenMPI 1.3 / iWARP you should get around 8us latency using mpi
pingpong tests.

 
Andy Georgi wrote:
> Thanks again for all the answers. It seems that were was a bug in the
> driver in combination with
> Suse Linux Enterprise Server 10. It was fixed with version 1.0.146.
> Now we have 12us with NPtcp and
> 22us with NPmpi. This is still not fast enough but for the time
> acceptable. I will check the
> alternatives as soon as possible and look forward to OpenMPI 1.3. Then
> we will see what iWARP brings
> ;-).
>
> Best regards,
>
> Andy
>
> Kozin, I (Igor) schrieb:
>>> Thanks for the fast answer. So is this latency normal for TCP
>>> communications over MPI!? Could RDMA maybe reduce the latency? It
>>> should work with those cards but there are still problems with OFED.
>>> iWARP is also one of the features they offer but if it works...
>>
>> Hi Andy,
>> Yes, ~40us TCP latency is normal (it can be worse too).
>> If you need lower MPI latency you need to look elsewhere (but it's not
>> going to be TCP). Check SCore, OpenMX and Gamma. SCore is more mature of
>> the three but OpenMX looks promising too. We get less than 15 us using
>> SCore MPI and Intel NICs (IMB PingPong). Of course commercial MPI
>> libraries offer low latency too e.g. Scali MPI.
>>
>> Best,
>> Igor
>>
>>> --
>>>
>>> Dresden University of Technology
>>> Center for Information Services
>>> and High Performance Computing (ZIH)
>>> D-01062 Dresden
>>> Germany
>>>
>>> e-mail: Andy.Georgi_at_[hidden]
>>> WWW: http://www.tu-dresden.de/zih
>>>
>>> _______________________________________________
>>> users mailing list
>>> users_at_[hidden]
>>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>>
>> I. Kozin (i.kozin at dl.ac.uk)
>> Computational Science and Engineering Dept.
>> STFC Daresbury Laboratory Daresbury Science and Innovation Centre
>> Daresbury, Warrington, WA4 4AD skype: in_kozin
>> tel: +44 (0) 1925 603308
>> fax: +44 (0) 1925 603634
>> http://www.cse.clrc.ac.uk/disco
>>
>>
>> _______________________________________________
>> users mailing list
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>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>>
>>
>