https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/OMP-NUM-THREADS-and-MKL/m-p/882992#M9753 Hi,<BR />being a novice with MKL usage on DualCore machine, I am completely confused...<BR /><BR />I have a FORTRAN code, which is dominated by BLAS/LAPACK calls, no OMP pragmas.<BR />The code is compiled by ifort with -openmp, and linked to MKL library.<BR />Running this code with no OMP_NUM_THREADS set, or with =1, I got faster time comparing with run with OMP_NUM_THREADS=2. <BR /><BR />I thought that I will see an improvement, by allowing MKL to use 2 cores, but the result is oposite.<BR />What can be wrong??<BR /><BR /><BR /> Wed, 14 Feb 2007 16:01:03 GMT valera_veryazov 2007-02-14T16:01:03Z https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/OMP-NUM-THREADS-and-MKL/m-p/882992#M9753 Hi,<BR />being a novice with MKL usage on DualCore machine, I am completely confused...<BR /><BR />I have a FORTRAN code, which is dominated by BLAS/LAPACK calls, no OMP pragmas.<BR />The code is compiled by ifort with -openmp, and linked to MKL library.<BR />Running this code with no OMP_NUM_THREADS set, or with =1, I got faster time comparing with run with OMP_NUM_THREADS=2. <BR /><BR />I thought that I will see an improvement, by allowing MKL to use 2 cores, but the result is oposite.<BR />What can be wrong??<BR /><BR /><BR /> Wed, 14 Feb 2007 16:01:03 GMT https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/OMP-NUM-THREADS-and-MKL/m-p/882992#M9753 valera_veryazov 2007-02-14T16:01:03Z https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/OMP-NUM-THREADS-and-MKL/m-p/882993#M9754 <P>Hi,</P> <P>May be the problem is with your method of measuring running time. If you are using cpu_time(), then take into account that this function returns total time consumed on both CPU's, e.g. if your program ran for 1 minute with total load of both processors, this function will return 2 minutes (1 min for one CPU +1 min for another one), which would compare unfavorably to the running time on 1 CPU due to some overhead.</P> <P></P> <P></P> Thu, 15 Feb 2007 06:27:26 GMT https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/OMP-NUM-THREADS-and-MKL/m-p/882993#M9754 izryu 2007-02-15T06:27:26Z https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/OMP-NUM-THREADS-and-MKL/m-p/882994#M9755 Thanks! It was indeed my stupidity - to look at CPU time :(<BR /> Thu, 15 Feb 2007 11:24:50 GMT https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/OMP-NUM-THREADS-and-MKL/m-p/882994#M9755 valera_veryazov 2007-02-15T11:24:50Z