[Difx-users] [Difx-developers] INQUIRY: Processing correlation environment {External}

[Adam Deller]

Hi Takehiro,

Generally speaking, DiFX is pretty robust to having servers with different
capabilities, since the time division multiplexing that is used will
happily allocate fewer subintegrations to the slower nodes and more to the
faster ones. If the throughput does not go up when you add more processing
resources, you are not compute bound, but must instead be either:

1) input voltage read bound;
2) output visibility write bound; or
3) network I/O bound (either a) in the voltage send from the datastream
reading nodes, or b) in the visibility subintegration assembly at the
manager node)

It would be fairly rare for case 2) to be the problem, unless you have
short integration times, many baselines, and many channels. If you have a
decent network, and you are not doing very short subintegrations with lots
of channels, it would also be unusual for case 3b) to be the problem.  So
that leaves the voltage data read or send - either getting it off disk in
the first place, or away from the read node to the processing nodes.

Can you let us know what your correlator topology is? Is this reading from
commodity disk, Mark5/Mark6, or...? What hardware are the datastream nodes
running on, and what network connectivity do they have? And what is the
read rate that is being achieved (i.e., what is the per-antenna datarate,
and the correlation speed-up factor [correlate time divided by obs time for
a given job]?)

Cheers,
Adam

On Mon, 6 Jul 2026 at 20:47, 西 健宏 via Difx-developers <
difx-developers at listmgr.nrao.edu> wrote:

> Dear colleagues,
>
> Hello.
> My name is Takehiro Nishi, in the Geospatial Information Authority of
> Japan (GSI).
> GSI is responsible for correlating some of the geodetic VLBI sessions of
> IVS.
>
> I'm writing to inquire about processing correlation environment.
>
> Currently, GSI is trying to improve the processing speed of "DiFX", since
> the processing time didn’t improve when we added three new servers for
> distributed processing.
> We need to optimize our system, but we are not sure where the bottle neck
> is.
> Therefore, I would appreciate it if you could inform us of your processing
> environment to help our investigation as below:
>
>         ・the number of processes written in .machines files     :
>         ・the number of threads written in .threads files                :
>         ・the capacity of memory for each server                 :
>         ・the total number of cores                              :
>         ・the total number of processing servers                 :
>         ・Are the number of cores and memory on the servers uniform, or are
> they varied?
>                 :
>
> Thank you for your cooperation.
>
>
> Best regards,
> Takehiro
> GSI
>
> ---------------------------------------------------------------
> Takehiro Nishi
> Space Geodesy Division
> Geodetic Department
> Geospatial Information Authority of Japan (GSI)
> E-mail: nishi-t96pc at mlit.go.jp
> ---------------------------------------------------------------
>
>
> _______________________________________________
> Difx-developers mailing list
> Difx-developers at listmgr.nrao.edu
> https://listmgr.nrao.edu/mailman/listinfo/difx-developers
>


-- 
!=============================================================!
Prof. Adam Deller
Centre for Astrophysics & Supercomputing
Swinburne University of Technology
John St, Hawthorn VIC 3122 Australia
phone: +61 3 9214 5307
fax: +61 3 9214 8797
!=============================================================!
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