Performance: Difference between revisions

# combining these two keywords gives the highest performance (see [[2VB1#XDS_processing]] for an example). As a rough guide, I'd choose them to be approximately equal; an even number for MAXIMUM_NUMBER_OF_PROCESSORS should be chosen because that fits better with usual hardware. If in doubt, use a lower number for MAXIMUM_NUMBER_OF_JOBS than for MAXIMUM_NUMBER_OF_PROCESSORS. Since 2017, XDS has an automatic feature that divides up the available cores into JOBS (operating system processes) running with multiple cores each. You use this automatic feature when you run <code>xds_par</code>, and don't specify MAXIMUM_NUMBER_OF_JOBS.

# NUMBER_OF_IMAGES_IN_CACHE avoids repeated (3-fold) reading of data frames in the INTEGRATE task during processing of a batch of frames. This comes at the expense of memory (RAM) and is discussed in [[Eiger]]. The default is DELPHI/OSCILLATION_RANGE+1 and is usually adequate. Only on low-memory systems (e.g a 8GB RAM machine for processing Eiger 16M data collected with 0.1° oscillation range, at DELPHI=5 and MAXIMUM_NUMBER_OF_JOBS=1) should this be set to 0, to conserve memory and avoid slow processing due to thrashing, or even killed XDS processes. If the cache size of a process exceeds 8GB, XDS will print a warning, and in that case the user has to explicitly include a NUMBER_OF_IMAGES_IN_CACHE=<desired number> line in XDS.INP, to confirm that actually so much memory should be used. '''Typically, you don't specify NUMBER_OF_IMAGES_IN_CACHE'''.

# the next thing to consider is [http://www.mpimf-heidelberg.mpg.de/~kabsch/xds/html_doc/xds_parameters.html#DELPHI= DELPHI] together with [http://www.mpimf-heidelberg.mpg.de/~kabsch/xds/html_doc/xds_parameters.html#OSCILLATION_RANGE= OSCILLATION_RANGE]: if DELPHI (the rotation range of a ''batch'' of frames) is an integer multiple of MAXIMUM_NUMBER_OF_PROCESSORS * OSCILLATION_RANGE that would be good because it nicely balances the usage of the threads. For this purpose, you may want to change (if possible, raise) the value of DELPHI (default is 5 degrees). If you are doing fine-slicing then mis-balancing of threads is not an issue - but for those users who want to collect 1° frames (which I think is not the best way nowadays ...) it should be a consideration. Additional consideration: the total number of frames should be an integer multiple of the intended number of frames in a batch. Example: 360 frames of 0.5° can be processed on a 8-core machine optimally by specifying DELPHI=4, since then there are 8 frames in a batch and the complete dataset has 45 batches. For weak data one should consider raising DELPHI to 12; that would give 15 batches. A trick: if you want to use DELPHI=8 in this situation then just specify DATA_RANGE=1 368 (pretending 23 batches of 8°) instead of DATA_RANGE=1 360 . XDS will complain about the missing 8 frames, but that has no adverse effects except that no FRAME.cbf will be produced. All of this doesn't matter for a single dataset, but for mass processing of datasets it does make a difference.  

# performance-wise, I/O also plays a role because as soon as you run 24 or so processes then a single GB ethernet connection may be limiting. OTOH shell-level parallelization smoothes the load.