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Subject: Re: [OMPI users] TCP Latency
From: Andy Georgi (Andy.Georgi_at_[hidden])
Date: 2008-07-30 07:38:10


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
> users_at_[hidden]
> http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>

-- 
Dresden University of Technology
Center for Information Services
and High Performance Computing (ZIH)
D-01062 Dresden
Germany
Phone:    (+49) 351/463-38783
Fax:      (+49) 351/463-38245
e-mail: Andy.Georgi_at_[hidden]
WWW:    http://www.tu-dresden.de/zih