Sun Performance Library and OpenMP applications

Question

Hi list,
I have a code that uses BLAS/Lapack libraries. This code requires the BLAS/Lapack to run in serial mode. If and when it runs in parallel this is a disaster. The code runs in parallel with OpenMP directives in SMP systems. I specify the number of threads by setting
OMP_NUM_THREADS
to the number of threads desired. Unfortunately if OMP_NUM_THREADS > 1 then sunperf runs in parallel as well. Is there anyway to tell to the sunperf library to run in serial mode no matter what the value of OMP_NUM_THREADS is?
For example GOTO BLAS library provides the environmental variable GOTO_NUM_THREADS which is dedicated to the threads of the GOTO library. So by setting GOTO_NUM_THREADS = 1, the library always runs in serial mode no matter what the value of OMP_NUM_THREADS is.
How could I achieve the same effect with Sun Performance Library?

Answer 1

Take a look at Perflib's USE_THREADS routine :
man -s 3p use_threads
Doing a call to USE_THREADS with the value of "1", before calling Perflib routines may work for you.
Also, I've noticed applications that have lots of small chunks of parallel work, need the threads to be very responsive. (And not sleep in between work chunks)
A way to make the threads not sleep is with the ${SUNW_MP_THR_IDLE} environment variable. I always set the value to "SPIN" :
% setenv SUNW_MP_THR_IDLE SPIN
You can see other settings for this in the OpenMP User's Guide, page 18 :
http://docs.sun.com/app/docs/doc/819-5270
Hope this helps.