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SimFactory/ranger-intel11.cfg: Are BLAS and LAPACK compilations on Ranger optimized?
ranger-intel11.cfg now sets BLAS and LAPACK to be built along with the Cactus and other external libraries. Usually the host system BLAS and LAPACK are fine tuned to take advantage of the particular memory hierarchy of the host machine. I was wondering if this fine tuning is performed when we set BLAS = BUILD or LAPACK = BUILD, and, in case it is not, if it would be interesting to define Cactus env variables to set the size of the several cache memories for example and use it for this necessary fine tuning.
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I don't like the trend towards building our own versions of libraries on each machine. I see this as a fallback in case there is some problem with the system libraries.
As Bruno points out, the system versions of libraries might well be optimised or tailored in some other way to the particular machine. Unless there is some problem with the system version (e.g. it has not been built with all required options), I prefer to use that. This will save on compilation time, disk space, and confusion if you have to report an error and the machine admin finds that you are using a nonstandard installation of a library.
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I agree.
The current "trend" towards building these libraries on our own comes from the fact that not many people contribute good settings for these libraries, and so I choose the easiest way (for me) when creating or updating option lists. I would be most happy about contributions.
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These options
BLAS_DIR = NO_BUILD BLAS_LIBS = -mkl
LAPACK_DIR = NO_BUILD LAPACK_LIBS = -mkl
should do most of the trick.
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Committed.
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The standard BLAS and LAPACK libraries that are distributed with Cactus are not optimised for a particular machine. Yes, it would be interesting to use e.g. the MKL instead.
Since most Cactus users do not solver large linear systems, the performance of BLAS and LAPACK is probably not that important.