When I use MAGMA with GotoBLAS the LAPACK results are sometimes wrong. Only some cases are wrong, but those that are wrong are consistently wrong, either with GotoBLAS with multiple threads or with only one thread. When I use the reference BLAS of Ubuntu Linux the problem cases then work. The nature of the failure is that after a certain point the results are different but not grossly so. The calculation returns a success code.
I am using a computer with an Intel I7 processor and 8 Gbytes of memory, running Ubuntu Linux 10.4 (64 bit). This is a new system for me which I bought specifically to hold an NVIDIA GTX 460 (with 2 GBytes memory) in order to explore GPGPU calculations using CUDA and MAGMA.
The process monitoring software reports the computer as having 8 CPU's, but I believe these to be on four cores, each behaving as if it is two processors.
I think this background is relevant to the problems I am having.
When I installed GotoBLAS I allowed it to choose the number of threads and it chose 8. I notice in practice that four cores show 100 % usage and the others a low but variable figure while the LAPACK calculations are being done as part of the MAGMA test cases.
1. Are there any specific configuration that I should do to use GotoBLAS with MAGMA? I have found nothing in the MAGMA documentation but in the GotoBLAS documentation there is some mention of some system modifications to use large memory pages. Should I implement that? Has anyone experience of doing that?
2. Has anyone experienced similar problems? Could this be in some way hardware specific?
3. Can anyone recommend an alternative strategy to get a multithreaded BLAS? The single threaded BLAS shows much slower speeds on both CPU and GPU calculations.
I have had a brief look around on the internet to see if there is any other information. I would welcome any suggestions as to where I could look.
Thank you for reading this.
P.S. Since writing this I have found the following comment on line:
(NB GotoBLAS2 won't work on the i7 series though).
at this location: http://ccl.net/cgi-bin/ccl/message-new?2010+11+06+005
I am attempting to contact the author of the comment.