------- Comment #13 from nmm1 at cam dot ac dot uk 2009-11-10 13:32 ------- Oh, joy. This went soft yesterday, and today I can't repeat the effects. I have some of the evidence in Email I sent to the ACML expert, who has managed to repeat them at least once. But, at BEST, the effects seem to depend on static/dynamic linking, Clib versions, Old Uncle Tom Cobbley and all. Here is the main effect I was reporting:
gosset$gfortran -Wall -std=f2003 -pedantic -O3 -fopenmp -o Cholesky_one_f \ gosset> Answers/Cholesky/one.f90 -lacml_mp gosset$./Cholesky_one_f fred_f_1000 Error in calling LAPACK Instrumenting the source showed that was INFO=15, which indicates that pivot 15 was zero, which is ridiculous. And it is THAT one which was the bug that primarily concerned me. I may have made some mistakes in identifying the performance issues. Given where the OpenMP directives are in the solver, some slowdown is to be expected. That is clearly not a bug. I distinctly remember having to break in after 4+ minutes using gfortran 4.3.2, when the 'normal' time was about 30 seconds. That could be a Linux scheduler problem, of course. Until and unless I can produce some more demonstrably incorrect performance, I suggest ignoring that aspect of my report. If I can't repeat it, either I got myself confused, or it will be too evil to justify the effort of investigating. In either case .... -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41977
