My Community

hi,

at the moment we are trying to optimize VASP for an IBM power6 machine. This parameter -DCACHE_SIZE what is it actually for? And more important how can you find/calculate what value you should use(or start from as a good estimate)

A power6 machine ahe 64kb L1 cache, 4Mb L2 per core and 32Mb L3 per core...

thanks
Danny

It's ostensibly the size of the L1D cache in units of DP FP variables. That should give you a starting point. Compile with different values and benchmark to find the best.

Though if you use FFTW instead of the built-in FFT library it's shouldn't matter that much. You should probably be using FFTW, in my recent benchmarks on a quad-core Opteron using FFTW improved performance by about 25 %.