Low frequency pulsar surveys and supercomputing
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Low-Frequency Pulsar Surveys and Supercomputing. Matthew Bailes. Outline:. Baseband Instrumentation MultiBOB MWA survey vs PKSMB survey Data rates CPU times Low-Frequency Pulsar Monitoring The Future Supercomputers. Pulsar “Dedispersion”. Incoherent. Coherent Dedispersion.

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Low frequency pulsar surveys and supercomputing

Low-Frequency Pulsar Surveys and Supercomputing

Matthew Bailes


Outline

Outline:

  • Baseband Instrumentation

  • MultiBOB

  • MWA survey vs PKSMB survey

  • Data rates

  • CPU times

  • Low-Frequency Pulsar Monitoring

  • The Future Supercomputers


Pulsar dedispersion

Pulsar “Dedispersion”

  • Incoherent


Coherent dedispersion

Coherent Dedispersion

  • Unresolved on us timescales

  • From young or millisecond pulsars

  • Power-law distribution of energies

PSR J0218+4232


1022 1001 pulsar timing kramer et al

1022+1001 Pulsar Timing (Kramer et al.)


Cpsr2 timing hotan bailes ord

CPSR2 Timing (Hotan, Bailes & Ord)


Swinburne baseband recorders etc

Swinburne Baseband Recorders etc

  • 1998: Canadian S2 to computer (16 MHz x 2)

    • 100K system + video tapes

  • 2000: CPSR

    • 20 MHz x 2 + DLT7000 drives x 4

  • 2002: CPSR2

    • 128 MHz x 2 + real-time supercomputer (60 cores)

  • 2006: DiFX (Deller, Tingay, Bailes & West)

    • Software Correlator (ATNF adopted)

  • 2007: APSR

    • 1024 MHz x 2 + real-time supercomputer (160 cores)

  • 2008: MultiBOB

    • 13 x 1024 ch x 64us + fibre + 1600-core supercomputer


Dspsr software

dspsr software

  • Mature

  • Delivers < 100 ns timing on selected pulsars

  • Total power estimation every 8us with RFI excision

  • Write a “loader”

  • Can do:

    • Giant pulse work

    • Pulsar searching (coherent filterbanks)

    • Pulsar timing/polarimetry

    • Interferometry with pulsar gating


Psrdada van straten

PSRDADA (van Straten)

  • psrdada.sourceforge.net

  • Generic UDP data capture system (APSR/MultiBOB)

  • Ring Buffer(s)

    • Can attach threads to fold/dedisperse etc

    • Hierachical buffers

    • Shares available CPU resources/disk

    • Web-based control/monitoring

  • Free! + hooks to dspsr & psrchive.


Low frequency pulsar surveys and supercomputing

APSR

  • Takes 8 Gb/s voltages

  • Forms:

    • 16 x 128 channels (with coherent dedispersion)

    • 4 Stokes, umpteen pulsars

    • Real-time fold to DM=250 pc/cc.

  • O(100) Ops/sample

    • Sustaining >>100 Gflops

  • ~100K computers.

  • June 2008

  • 192 MHz working @ 4bits

  • 768 MHz working @ 2bits


Coherent dedispersion bw time

Coherent Dedispersion BW/time

1024

x

(100K)

BW

128

(300K)

x

16 20

x

x

1998 2000 2002 2004 2006 2008

year


Coherent dedispersion1

Coherent Dedispersion

  • Now “trivial”

  • FFT ease ~ B-2/3


Multibob

MultiBOB

  • High Resolution Universe Survey (PALFA of the South)

  • Werthimer’s iBOB boards

    • 1024 channels, down to 10us sampling

    • Two pols

  • FPGA coding hard…

    • Use software gain equalizer/summer

  • ~5 MB/s beam

  • 1 Gb/s Fibre to Swinburne (>1000 km fibre)

  • Real time searching!


New pks mb survey

New PKS MB Survey:

  • Kramer

  • 13 beams

  • 70 minutes/pointing

  • 1024 channels

  • 300 MHz BW

  • 64 us sampling

  • +/- 3.5 deg

  • Bailes

  • 13 beams

  • 9 minutes/pointing

  • 1024 channels

  • 300 MHz BW

  • 64 us sampling

  • +/- 15 deg

  • Johnston

  • 13 beams

  • 4.5 minutes/pointing

  • 1024 channels

  • 300 MHz BW

  • 32 us sampling

  • The rest


Low frequency pulsar surveys and supercomputing

MWA

  • Samples

    • Takes (24x1.3MHz=32 MHz) x 2 x 512

    • “Just” 32 GB/s (64 Gsamples/s)

  • FFTs it

    • (5 N log2 ops/pt = 2.2 Tflops)

  • XMultiplies & adds

    • (512)*256*B*4 = 16 TMACs


Sensitivity

32 vs 288 MHz

~3-5x PKS

700 vs 0.6 deg2

350 vs 25 K

Sensitivity:

(folded factor)


Pks vs mwa

~ Parity

PKS vs MWA

  • G ~ 3-5 x better

  • Tsys ~ 14 x worse ?

  • B1/2 ~ 3 x worse

  • Flux ~ 25 x better (1400 vs 200 MHz)

  • t1/2 ~ 32 x better

Single Pulse work ~ Comparable

Coherent search ~ 32x improvement!

But: There is a limit to the time you can observe a pulsar!

4m vs 144m -> 5x deeper.


Scattering b 0

Scattering b=0

  • 1,10,100,1000ms


Scattering b 5d

Scattering b=5d

  • 1,10,50,100ms


Low frequency pulsar surveys and supercomputing

b=30

  • 0.5,1ms


Search instrumentation

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Correlator

Us

Search instrumentation?

Volts

Spectra

Visibilities

FBanks

uv

32 MHz

Dedisp

F

X

Grid

2D FFT-1

36 GB/s

x 512

x 512 x 256

x 1922

x 512

36 GB/s

1024 GB/s

32 bits

600 GB/s

30 GB/s

5 bits

200 GB/s

32 bits

Fold

FFT

Spectra

Pulsars

<1 bit/s


Search timings

Search Timings

  • 36,000 “coherent beams” (768m/4m=192)2

  • 36 gigapixels/s

  • Dedisperse/CPU core

    • Gigapixel/120s

    • 36 x 120 = 4320 cores = 500 machines = 250 kW

  • NFFT = 36,000 * 1024 (DMs)/8192 = 4608 FFTs/sec

  • Seek (3s / 8192 x 1024 pt FFT)

    • 14,000 cores ~ 1800 machines = MW. (M$/yr)


Low frequency pulsar surveys and supercomputing

Supercomputing @ Swinburne

The Green Machine

  • installed May/June 2007

  • 185 Dell PowerEdge1950 nodes

    • 2 quad-core processors

      (Clovertown: Intel Xeon 64-bit 2.33 GHz)

    • 16GB RAM

    • 1TB disk -> 300 TB total

  • 1640 cores/14 Tflops

  • dual channel gigabit ethernet

  • CentOS Linux OS

  • job queue submission

  • 20 Gb infiniband (Q1 2008)

  • 83 kW .vs. 130 kW cooling

Machines: ~1.2M

Fuel: ~100K/yr


Search times

Search Times:

  • Depend only upon:

    • Npixels x Nchans x Tsamp-1

  • Requires:

    • No acceleration trials

  • PSR J0437-4715

    • In 8192s, small width from acceleration


Search timings 32x32 tiles

Search Timings (32x32 tiles)

  • 36000->1024 “coherent beams”

  • 36->1 gigapixels/s

  • Dedisperse/core

    • Gigapixel/120s

    • 120 = 120 cores = 15 machines = 7 kW

  • NFFT = 1024 * 1024 (DMs)/8192(s/FFT) = 128 FFTs/sec

  • Seek (3s / (8192 x 1024) pt FFT)

    • 378 cores ~ 50 machines = 25 kW.


Rrats

RRATs

  • Log N - Log S (helps with long pointings…)

  • 1000 x integration time.

  • Maybe good RRAT finder.


Monitoring

Monitoring:

Monitoring?


Monitoring1

Monitoring:


Build your own telescope

Build Your Own Telescope?

  • May be cheaper to build dedicated PSR telescope than attempt to process everything from existing telescopes!

  • 32x32 tile: (2D FFT - 1D FFT - dedisperse - FFT)

    • ~2M telescopes

    • ~2M “beamformer/receivers”

    • ~1M correlator

    • ~1M Supercomputer

    • ~1M construction

    • ~7-8M


Next gen supercomputers io or tflops

Next-Gen Supercomputers (IO or Tflops?)

  • Infiniband 20 Gb (40Gb)

    • 288 port switch

    • ~10 Tb/s IO Capacity (1-2K/node)

  • Teraflop CPU capacities/node (140 Gflops now)

  • Teraflop Server or Tflop GPU?

    • 10 GB/s vs 76 GB/s

  • Power (0.1W/$)

    • 2M = 200 kW


Architecture 2011

Architecture (2011??):

288 Ports

40 Gb/s

144 Tflops

288 Ports

40 Gb/s

144 Tflops

FX

300K

~1M

300K

~1M


Summary

Summary:

  • Strong motivation for multiple (~100) tied array beams

    • PSRs/deg^2

  • Surveys only possible with compact configurations

    • At present

  • Future Supercomputers may allow search even with MWA-like telescopes


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