This is a note Martin wrote about speeding up ECHOMOP on OSF/1 systems
It has recently become possible to implement the Starlink NDF/HDS system file mapping features under OSF/1. A new version of echomop will be released in 1995/Q4 which will be linked to use the new HDS. This should give significant performance gains under OSF/1, typically echomop reduction operations 1 to 8 are completed in one fifth of the time. The overall loading of your machine will also be reduced.
It is possible to implement a ramdisk (as described recently in a Starlink newsgroup) to achieve a further improvement in reduction speed. My own tests gave the following results:
Machine: zuaxp0, DEC Alpha 2000/300, OSF/1 v3.2.
Data: UCLES, 1024x512 pixel CCD images.
NDisk = data on remote nfs disk.
LDisk = data on local disk.
RDisk = data on RAM disk.
Test U.CPU S.CPU Elasped %CPU Nomap/NDisk 72 165 21:30 18 Nomap/RDisk 73 96 5:12 54 Map/NDisk 43 11 4:07 22 Map/Ldisk 43 6 3:35 22 Map/RDisk 42 10 2:03 41
You can see that the mapping-HDS/ramdisk combination is about ten times faster than a "normal" reduction. Allowing for to-from ramdisk copying (~30s), a factor eight recuction in elapsed time is still possible.
Generally it's a good idea to run echomop on the same machine as the disk which is storing the data. You can expect to save about 12% on elasped time by this means.
Martin Clay newsgroup posting on echelle reduction and ramdisks is here. Go back to the EDR home page.
Martin Clayton