IPAC 2MASS Working Group Meeting #87 Minutes

IPAC 2MASS Working Group Meeting #87 Minutes, 2/27/96

Attendees: R. Beck, R. Cutri, T. Evans, J. Fowler, L. Fullmer, T. Jarrett, D. Kirkpatrick, G. Kopan, B. Light, H. McCallon

AGENDA

  1. Updated 2MAPPS Schedule
  2. User CPU Variation Report
  3. Ultrasparc Loaner
  4. Coadd Kernel Study
  5. WSDB SIS Definition

DISCUSSION

  1. Updated 2MAPPS Schedule -- The task of updating the 2MAPPS schedule discussed at the previous meeting has been completed, and copies of the new schedule were distributed to the members present. Copies were put in the mailboxes of members not present.

  2. User CPU Variation Report -- G. Kopan reported on a test he has been doing to study the variation of user CPU time consumed on identical tasks. It appears that consistent access of memory locations spanning over a megabyte thrashes the processor cache, and once such thrashing begins, the user CPU, system CPU, and throughput time vary significantly. If the memory spanned is just under a megabyte, no thrashing is seen, and the times are all nearly constant over repeated runs of the identical task. The test program and output are appended to these minutes. The implications are that wherever possible, consistent access of memory locations more than a megabyte apart in memory should be avoided (note that this could take the form of a window moving through memory with accesses occurring at the beginning and end of the window and a width of over 1 MB). J. Fowler will look into ways to reduce such access in DFLAT, where the processing of 256x256 REAL*4 arrays involving the use of five arrays at a time might be reorganized.

  3. Ultrasparc Loaner -- We have been asked by the Tools Group how long we need the Ultrasparc loaner from Sun and when we need it. It was not clear whether extra time implied extra cost to IPAC. J. Fowler agreed to get these details. [After the meeting, R. Scholey provided the following information: The loaner involves no cost to IPAC, but Sun is reluctant to make it available for more than one week; it is expected to arrive within a week or so.]

  4. Coadd Kernel Study -- T. Jarrett reported on a study of the effects on galaxy processing that result from varying the coadding kernel. Three approaches have been used: bilinear interpolation, area overlap, and the "Weinberg kernel". The latter involves smoothing the input before coadding, and the smoothing function can be anything, but a Gaussian comparable in size to a typical 2MASS point spread function was used in the tests. The area overlap kernel produces the sharpest images (i.e., images appearing to contain more power in high spatial frequencies). The Weinberg kernel provided slightly more faint galaxies when the output was processed by GALWORKS, but slightly more false extractions also resulted. The differences between the three kernels were very small. A more complete report is being prepared by T. Chester.

  5. WSDB SIS Definition -- R. Cutri discussed the data to be included in the Working Survey Data Base (WSDB) needed to support the final data products. He has put together a draft specification that identifies parameters and formats. This will be distributed, and ideas for adding, removing, or changing items are solicited.

    One aspect that became clear was that the size of the point source record that BANDMERGE has to handle will probably become larger, making it possible for memory allocation to be a problem. As a result, J. Fowler requested that the MAP01 SIS be changed to include a requirement for each line of ASCII text to be the same length so that the corresponding files could be read as direct access files. This will allow BANDMERGE to read only the parts of the files needed for band merging and then to include the other information efficiently in the output. T. Evans stated that this would not be a problem, although it would require a blank space at the end of each line to correspond to the final "|" delimiter in the header lines, but otherwise the only change would be to pad out the comment lines to the same length as the data lines.

    Team members are requested to review the sample WSDB to be distributed by R. Cutri and send responses to him.

Addendum: Code and Results From User-CPU Tests

c    thrash the cache

      parameter (nbuf=2**20)
      byte s(nbuf),d(nbuf)

      loop=2**24/nbuf
      print *,loop,nbuf

      do i=1,nbuf
      s(i)=1
      enddo

      do j=1,loop
      do i=1,nbuf
      d(i) = s(i)
      enddo
      enddo

      stop
      end

    4  4194304  8.88u 0.37s 0:09.36 98.8%
    4  4194304 17.72u 0.46s 0:18.41 98.7%
    4  4194304 17.74u 0.49s 0:18.41 99.0%
    4  4194304 17.85u 0.38s 0:18.43 98.9%
    4  4194304 17.53u 0.44s 0:18.24 98.5%
    4  4194304 17.86u 0.46s 0:18.48 99.1%
    4  4194304 17.82u 0.49s 0:18.56 98.6%
    4  4194304 17.93u 0.40s 0:18.47 99.2%
    4  4194304 17.88u 0.47s 0:18.64 98.4%
    4  4194304 17.92u 0.46s 0:18.56 99.0%
    8  2097152  5.46u 0.27s 0:05.79 98.9%
    8  2097152 16.21u 0.20s 0:16.54 99.2%
    8  2097152 16.24u 0.20s 0:16.55 99.3%
    8  2097152 16.61u 0.26s 0:16.97 99.4%
    8  2097152 16.79u 0.21s 0:17.13 99.2%
    8  2097152 16.68u 0.25s 0:17.07 99.1%
    8  2097152 16.68u 0.23s 0:17.06 99.1%
    8  2097152 16.66u 0.26s 0:17.06 99.1%
    8  2097152 16.75u 0.28s 0:17.13 99.4%
    8  2097152 12.44u 0.21s 0:12.79 98.9%
   16  1048576 19.74u 0.11s 0:19.94 99.5%
   16  1048576 19.74u 0.16s 0:20.11 98.9%
   16  1048576 19.71u 0.17s 0:20.08 99.0%
   16  1048576 19.80u 0.14s 0:20.06 99.4%
   16  1048576 19.74u 0.10s 0:19.99 99.2%
   16  1048576 19.75u 0.11s 0:19.96 99.4%
   16  1048576 19.82u 0.06s 0:19.98 99.4%
   16  1048576 19.49u 0.41s 0:20.00 99.5%
   16  1048576 19.84u 0.11s 0:20.07 99.4%
   16  1048576 19.82u 0.15s 0:20.08 99.4%
   32   524288  4.60u 0.08s 0:04.81 97.2%
   32   524288  4.73u 0.12s 0:04.94 98.1%
   32   524288  4.54u 0.15s 0:04.87 96.3%
   32   524288  4.64u 0.11s 0:04.93 96.3%
   32   524288  4.69u 0.09s 0:04.86 98.3%
   32   524288  4.69u 0.09s 0:04.84 98.7%
   32   524288  4.73u 0.09s 0:04.90 98.3%
   32   524288  4.76u 0.07s 0:04.91 98.3%
   32   524288  4.66u 0.10s 0:04.86 97.9%
   32   524288  4.76u 0.12s 0:04.99 97.7%
   64   262144  4.62u 0.05s 0:04.70 99.3%
   64   262144  4.64u 0.08s 0:04.82 97.9%
   64   262144  4.65u 0.04s 0:04.78 98.1%
   64   262144  4.65u 0.07s 0:04.97 94.9%
   64   262144  4.57u 0.10s 0:04.95 94.3%
   64   262144  4.55u 0.09s 0:04.71 98.5%
   64   262144  4.65u 0.05s 0:04.78 98.3%
   64   262144  4.60u 0.08s 0:04.78 97.9%
   64   262144  4.59u 0.08s 0:04.75 98.3%
   64   262144  4.61u 0.08s 0:04.74 98.9%