[daip] making msclean run faster

[Eric Greisen]

Deidre Hunter wrote:
> Eric or other AIPS supporters,
> 
> I am running multi-scale clean in IMAGR on a data cube of 2048x2048  
> images of a big galaxy. My test of 6 channels is still running after  
> 10 hours, so a full cube will take many CPU days. I am wondering if  
> AIPS is using all it can of the computer's 5 GB of memory. My activity  
> monitor suggests that there are frequent disk IOs and that only 2.3 GB  
> of memory are in use. Is there anything I can set in AIPS that might  
> allow IMAGR to use more memory and less disk IO?
> 
> I am running 31DEC08, updated with MNJs, on a 2 x 3 GHz dual-core  
> intel MacPro with MacOSX 10.5.6 and 5GB memory. The 31DEC08 was a  
> binary installation.

One think to look at is the verb SETMAXAP.  You might benefit from a 
larger pseudo-AP.  But the real questions are whether 2048x2048 is 
appropriate, which resolutions are you using, and whether the I/O is 
happening each time a channel starts up or at other times.  The I/O is 
likely to be slow when reading the full data set to strip out the 
desired channel for imaging.  If the I/O remains slow when using the 
work file which is a minimal version of that channel's UV data, then 
either you have a large number of points or your OS is unable to keep 
the work file in RAM for some reason (too many other active processes, 
some system parameter that limits the ram used in this way, ...).  You 
can look at the work file (class IMAGR) to see how big it is.  Perhaps 
you should be using multiple facets for 3D imaging issues and also for 
having each image fit fully in RAM while you use it.  SETFC will tell 
you about the former if you ask it nicely (IMSIZE=0, CELLS=0).

I have worked hard to have IMAGR use more RAM when possible, doing as 
much and as many facets as possible together in memory at once.  When I 
first saw your subject line I wondered if it is making images of too 
many facets at each cycle (another capability I added).  I just added in 
31DEC09 yet another adverb to limit that in some cases.

Eric Greisen