PSTSWM AlphaSC-1000 Serial Performance

Performance Studies using

PSTSWM

Date/Person:	January 4, 2002 / Patrick H. Worley
Platform:	Compaq AlphaServer SC at Pittsburgh Supercomputer Center (lemieux.psd.edu):
	760 ES45 4-way SMP nodes (1 GHz Alpha 21264C with 8MB L2 cache)
Environment:	Compaq Tru64 UNIX V5.1A
	Compaq Fortran Compiler X5.4A-1684-46B5P
Code Version:	6.8.2
Make Options:	MACH=alpha-sc COMM=mpi PRECISION=8 PERF=n WORKSPACE=22000000
Compilation Options:	f90 -O4 -assume accuracy_sensitive -math_library accurate -align dcommons -align records -arch host -tune host
or	f90 -O4 -assume noaccuracy_sensitive -math_library fast -align dcommons -align records -arch host -tune host
or	f90 -O5 -assume noaccuracy_sensitive -math_library fast -align dcommons -align records -arch host -tune host
Number of steps:	T5, T10, T21, T42: 241 or 481
	T85: 49 or 97
	T170: 49 or 97
Notes:	using PSTSWM Fortran routines for Fourier transforms and BLAS

As with most compilers, the Compaq Fortran compiler has a very large number of optimization options. While we have not experimented with these extensively, the initial indications are that the standard "safe" optimizations (labelled "-O4 accurate" here) do as well as the more agressive optimizations, at least for this code. For the full atmospheric model CCM/MP-2D, the use of the fast libraries has more impact, due to a heavy use of math intrinsics.
The performance is sensitive to the number of vertical levels (which is the second index). As the number of vertical levels increases, the performance is more dependent on bandwidth and latency to main memory. See the graphical summary for more details.