Hi, it all looks like we have a bug with prefetch with PGI 14.7 + cpu specific compilation options. We have a "signal 4 : illegal instruction (not reset when caught) " within MatMult_SeqAIJ_Inode. The only thing we see there than can bug is the prefetch thing... We were asking ourself two things: #1- Since we don't kow how to handle these kinds of functions (_mm_*), how ca we test them? Is the "example" in Configure.py:606 sufficient to validate a good/bad result? #2- How can we disable PETSC_Prefetch when doing the petsc configuration? Thanks, Eric On 12/03/2010 02:35 PM, Jed Brown wrote:
I just pushed some prefetch for (S)BAIJ kernels. The biggest win is for MatSolve_SeqSBAIJ_*_NaturalOrdering_inplace where this patch is showing 30 to 50% speedups on Core 2 and Opteron. The other kernels tend to improve by 20 to 30% on Opteron with less consistent improvements on Core 2 but usually near 20%.
I have not found any cases to be slowed down by this patch, provided the matrix does not fit in cache. If the matrix does fit in cache, then the non-temporal hint is bad and will cause matrix entries to be unnecessarily fetched from memory. I think the scenarios in which end-to-end performance is limited by matrix kernels where the entire matrix fits in cache are much more rare than those where the matrix does not fit in cache, thus I consider the non-temporal hint to be an unambiguous win. If anyone sees a negative performance impact, please report it.
Jed