NERSCPowering Scientific Discovery Since 1974

Cray Compiler Performance on Edison


Cray recommends using the default optimization (-O2) which is equivalent to the higher levels of optimization with other compilers. In addition, the -O3 and -Ofp3 options can improve performance on some codes.

These are the Cray optimization options we compared.  The quotations are from the Cray compiler on-line man pages.

Cray compiler options tested
default This is the default level of optimization provided by the compiler with no optimization options specified.
-O2 The numeric levels of optimization increase the amount of optimization as the number increases.  "Cray reserves the right to alter the specific optimizations performed at these levels from release to release."
-O3 See above.
-hfp3 This option relaxes the level of compliance to the IEEE floating point standards.
-O3 -hfp3 See above.
-haggress (Fortran only).  "[I]nternal compiler tables are expanded to accommodate larger loop bodies."

Cray compiler on Edison


The Cray default level of optimization gives a good level of performance for all these benchmarks.