PSTSWM AlphaSC-667 Serial Performance

Performance Studies using

PSTSWM

Date/Person:	April 17, 2000 / P. Worley
Platform:	Compaq AlphaServer SC at Oak Ridge National Laboratory (colt.ccs.ornl.gov):
	16 ES40 4-way SMP nodes (667 MHz Alpha 21264a with 8MB L2 cache)
Environment:	Digital UNIX V5.0; RMS 2.36
Code Version:	6.7.2
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:	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 Digital 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), a sensitivity that is not visible here. For examples, performance is particularly bad when the problem has 16 vertical levels. See the graphical summary for more details.