ATLAS contains architectural defaults allowing installers to skip most
of the empirical tuning, with different platforms using different gcc
versions. To see what gcc version was used to build archdefs for your
system, you can scope
GetBestGccVers in
ATLAS/CONFIG/src/probe_comp.c.
By default, ATLAS will search for this version on
your system during configure, and if it can't find it, it will select
the closest version number that it can find. Not even later versions
of the compiler are necessarily better to use, since both performance
and correctness regressions are relatively common. However, many users
wish to force ATLAS to use a particular gcc, even when they have many
different gccs installed. The easiest way to force ATLAS to use a
particular gcc for all C compilers is:
-C acg /full/path/to/your/gcc
If you specify only the name and not the path (eg., ``-C alg gcc-4.4'',
then ATLAS will search for the named compiler in your PATH variable. The
safest approach is to give the full path to the compiler if gcc choice
is critical to you. If you want also specify the gfortran to use,
additionally add the flag:
-C if /full/path/to/your/gfortran
IMPORTANT NOTE: If you use a different gcc than preferred version,
you may reduce performance. Therefore once
your build is finished, you should make sure to compare your achieved
performance against what ATLAS's architectural defaults achieved. See
Section [*] for details on how to do this.
If you can tolerate a long install time, you may also
want to tell ATLAS not to use the architectural defaults, as described
in Section [*].
R. Clint Whaley
2016年07月28日