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SCARIe FABRIC A pilot study of distributed correlation. Huib Jan van Langevelde Ruud Oerlemans Nico Kruithof Sergei Pogrebenko and many others…. What correlators do…. Synthesis imaging simulates a very large telescope by measuring Fourier components of sky brightness on each baseline pair

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scarie fabric a pilot study of distributed correlation

SCARIe FABRICA pilot study of distributed correlation

Huib Jan van Langevelde

Ruud Oerlemans

Nico Kruithof

Sergei Pogrebenko

and many others…

what correlators do
What correlators do…
  • Synthesis imaging simulates a very large telescope
    • by measuring Fourier components of sky brightness
    • on each baseline pair
  • Sensitivity is proportional to √bandwidth
    • optimal use of available recording bandwidth
    • by sampling 2 bits (4 level) at Nyquist rate
  • Correlator calculates ½N(N-1) baseline outputs
    • after compensating for the geometry of array
    • Integrates output signal to something relatively slow
    • and samples with delay/frequency resolution

huib 02/11/06

evn mkiv data processor at jive
EVN MkIV data processor at JIVE
  • Implements this in custom silicon
    • 16 stations input from tapes
    • now hard-disks and fibres
  • Input data is 1 Gb/s max
    • 1 or 2 bit sampled
    • up to 16 sub-bands
    • format includes time codes
  • “Super computer” 1024 chips
    • 256 complex correlations each
    • at 32 MHz clock
  • Around 100 T-operations/sec
    • 2 bit only!
    • Depends a bit how you do it

huib 02/11/06

Should next correlator also use special hardware?

next generation
Next generation…

Can be implemented on standard computing?

Time critical, keep up with input

example: LOFAR on BlueGene

Higher precision and new applications

Better sensitivity, interference mitigation, spacecraft navigation

Can CPU cycles be found on the Grid?

From 16 antenna @ 1Gb/s (eVLBI)

And growing…

To 1000s at 100 Gb/s (SKA)

Pilot projects FABRIC & SCARIe

Connectivity, workflow

Real-time resource allocation

LOFAR central processor

FABRIC eVLBI

SKA inner core (5km)

huib 02/11/06

tflops pflops
Tflops, Pflops…
  • 2 bit operations ⇒ floating point
    • Results in enormous computing tasks
    • Very few operations / bit
    • Some could be associated with telescope

huib 02/11/06

SKA not even in here…

Rough estimate based on XF correlation

scari e fabric
SCARIe FABRIC
  • EC funded project EXPReS (03/2006)
    • To turn eVLBI into an operational system
    • Plus: Joint Research Activity: FABRIC
      • Future Arrays of Broadband Radio-telescopes on Internet Computing
        • One work-package on 4Gb/s data acquisition and transport

(Jodrell Bank, Metsahovi, Onsala, Bonn, ASTRON)

        • One work-package on distributed correlation (JIVE, PSNC Poznan)
  • Dutch NWO funded project SCARIe (10/2006)
      • Software Correlator Architecture Research and Implementation for eVLBI
    • Collaboration with SARA and UvA
    • Use Dutch Grid with configurable high connectivity: StarPlane
    • Software correlation with data originating from JIVE
  • Complementary projects with matching funding
    • International and national expertise from other partners
    • Total of 9 man year at JIVE, plus some matching from staff
      • plus similar amount at partners

huib 02/11/06

aim of the project
Aim of the project
  • Research the possibility of distributed correlation
    • Using the Grid for getting the CPU cycles
    • Can it be employed for the next generation VLBI correlation?
    • Exercise the advantages of software correlation
      • Using floating point accuracy and special filtering
    • Explore (push) the boundaries of the Grid paradigm
      • “Real time” applications, data transfer limitations
  • To lead to a modest size demo
    • With some possible real applications:
      • Monitoring EVN network performance
      • Continuous available eVLBI network with few telescopes
        • Monitoring transient sources
        • Astrometry, possibly of spectral line sources
      • Special correlator modes: spacecraft navigation, pulsar gating
      • Test bed for broadband eVLBI research

Something to try on the roadmap for the next generation correlator,

even if you do not believe it is the solution…

huib 02/11/06

previous experience on software correlation
Previous experience on Software correlation
  • Builds on previous experience at JIVE
    • regular and automated network performance tests
      • Using Japanese software correlator from NICT
    • Huygens extreme narrow band correlation
      • Home grown superFX with sub-Hz resolution

huib 02/11/06

work packages
Work packages
  • Grid resource allocation
    • Grid workflow management
      • Tool to allocate correlator resources and schedule correlation
      • Data flow from telescopes to appropriate correlator resources
    • Expertise from the Poznan group in Virtual Laboratories
      • Will this application fit on Grid?
      • As it is very data intensive
      • And time-critical if not real-time
  • Software correlation
    • correlator algorithm design
      • High precision correlation on standard computing
      • Scalable to cluster computers
      • Portable for grid computers and interfaced to standard middleware
    • Interactive visualization and output definition
      • Collect & merge data in EVN archive
      • Standard format and proprietary rights

huib 02/11/06

basic idea
Basic idea
  • Use the Grid for correlation
    • CPU cycles on compute nodes
    • The Net could be crossbar switch?

huib 02/11/06

  • Correlation will be asynchronous
    • Based on floating point arithmetic
    • Portable code, standard environment
workflow management
Workflow Management
  • Must interact with normal VLBI schedules
    • Divide data, route to compute nodes, setup correlation
    • Dynamic resource allocation, keep up with incoming data!

Effort from Poznan, based on their Virtual Lab.

huib 02/11/06

topology
Topology

Slice in time

Every node gets an interval

A “new correlator” for every time slice

Employ clusters computers at nodes

Minimizes total data transport

Bottleneck at compute node

Probably good connectivity at Grid nodes anyway

Scales perfectly

Easily estimated how many nodes are needed

Works with heterogeneous nodes

But leaves sorting to compute nodes

Memory access may limit effectiveness

Slice in baseline

Assign a (or a range of) products to a certain node

E.g. two data streams meet in some place

Transport Bottleneck at sources (telescopes)

Maybe curable with multicast transport mechanism which forks at network nodes

Some advantage when local nodes at telescopes

Does not scale very simply

Simple schemes for ½N2 nodes

Need to re-sort output

But reduces the compute problem

Using the network as the cross-bar switch

huib 02/11/06

work packages1
Work packages
  • Grid resource allocation
    • Grid workflow management
      • Tool to allocate correlator resources and schedule correlation
      • Data flow from telescopes to appropriate correlator resources
    • Expertise from the Poznan group in Virtual Laboratories
      • Will this application fit on Grid?
      • As it is very data intensive
      • And time-critical if not real-time
  • Software correlation
    • correlator algorithm design
      • High precision correlation on standard computing
      • Scalable to cluster computers
      • Portable for grid computers and interfaced to standard middleware
    • Interactive visualization and output definition
      • Collect & merge data in EVN archive
      • Standard format and proprietary rights

huib 02/11/06

broadband software correlation
Broadband software correlation

Station 1

Station 2

Station N

EVN Mk4 equivalents

Raw data BW=16 MHz,

Mk4 format on Mk5 disk

From Mk5 to linux disk

Raw data 16 MHz,

Mk4 format on linux disk

DIM,TRM,CRM

Channel extraction

Extracted data

SU

Pre-calculated,Delay tables

DCM,DMM,FR

Delay corrections

Delay corrected data

Correlator

Chip

huib 02/11/06

Correlation. SFXC

Data Product

software correlation
Software correlation

Working on benchmarking

Single core processors so far

Different CPU’s available

Already quite efficient

More work on memory performance

Must deploy on cluster computers

And then on Grid

Organize the output to be used for astronomy

huib 02/11/06

side step data intensive processing
Side step: Data intensive processing

Radio-astronomy can be extreme

User data sets can be large

Few – 100 GB now

Larger: LOFAR, eVLBI, APERTIF, SKA

All data enter imaging

Iterative calibration schemes

Few operations per Byte

Parallel computing: not obviously suited for messaging systems

Task (data oriented) parallelization

Processing traditionally done interactively on user platform

More and more pipeline approaches

Addressed in RadioNet

Project ALBUS

resulted in Python for AIPS

Looking for extension in FP7

Interoperability with ALMA, LOFAR

But for user domain

huib 02/11/06

goal of the project
Goal of the project
  • Develop: methods for high data rate e-VLBI using distributed correlation
    • High data rate eVLBI data acquisition and transport
      • Develop a scalable prototype for broadband data acquisition
        • Prototype acquisition system
      • Establish a transportation protocol for broadband e-VLBI
        • Build into prototype, establish interface normal system
      • Interface e-VLBI public networks with LOFAR and e-MERLIN dedicated networks
        • Correlate wide band Onsala data on eMERLIN
        • Demonstrate LOFAR connectivity
    • Distributed correlation
      • Setup data distribution over Grid
        • Workflow management tool
      • Develop a software correlator
        • Run a modest distributed eVLBI experiment

huib 02/11/06

current evlbi practice
Current eVLBI practice

user correlator

parameters

observing schedule

in VEX format

earth orientation

parameters

field system

controls antenna

and acquisition

BBC &

samplers

correlator control

including model

calculation

output

data

Mk4

formatter

Mk4 data

in Mk5prop form

over TCPIP

Mk5

recorder

Mk5

playback

huib 02/11/06

fabric components
FABRIC components

GRID

resources data

user correlator

parameters

observing schedule

in VEX format

earth orientation

parameters

field system

controls antenna

and acquisition

resource allocation

and routing

correlator control

including model

calculation

DBBC

VSI

output

data

FABRIC

=

The GRID

VSIe??

on??

PC-EVN

#2

huib 02/11/06

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