https://community.intel.com/t5/Intel-Moderncode-for-Parallel/matrix-multiplication/m-p/889936#M3744 hello sir,<BR /> its advisable to use as many no. of software threads as there are hardware threads..<BR />since your machine has only 2 hardware threads, its more than enough to use 2 threads..<BR />Also, we can see a significant increase in performance only in the case of bigger programs or applications.. So dont get confused if the parallel run time is higher for ur multiplication.. <BR /> Thu, 22 Nov 2007 12:40:55 GMT ashoksaravanan 2007-11-22T12:40:55Z https://community.intel.com/t5/Intel-Moderncode-for-Parallel/matrix-multiplication/m-p/889934#M3742 I am a newbie in thread programming, so sorry if my following question sounds stupid. I made a single threaded routine that multiplies two 5x5 matrices. I made another routine, 25 threaded, multiplying the pairs mat_1(line_i) x mat_2(column_j) for the same two matrices (I have a dual core processor). Why the multi-threaded routine is slower than the first one ? Is this true or have I made something wrong ? Wed, 21 Nov 2007 16:16:50 GMT https://community.intel.com/t5/Intel-Moderncode-for-Parallel/matrix-multiplication/m-p/889934#M3742 rdabra 2007-11-21T16:16:50Z https://community.intel.com/t5/Intel-Moderncode-for-Parallel/matrix-multiplication/m-p/889935#M3743 A short answer: the problem is too small to overcome the overhead of threading. Probably too small to time accurately, if you did it efficiently without threading. If you test a professionally written function, such as DGEMM from Intel MKL library, you will see that it drops to a single thread for problems of this size.<BR /> Wed, 21 Nov 2007 16:57:44 GMT https://community.intel.com/t5/Intel-Moderncode-for-Parallel/matrix-multiplication/m-p/889935#M3743 TimP 2007-11-21T16:57:44Z https://community.intel.com/t5/Intel-Moderncode-for-Parallel/matrix-multiplication/m-p/889936#M3744 hello sir,<BR /> its advisable to use as many no. of software threads as there are hardware threads..<BR />since your machine has only 2 hardware threads, its more than enough to use 2 threads..<BR />Also, we can see a significant increase in performance only in the case of bigger programs or applications.. So dont get confused if the parallel run time is higher for ur multiplication.. <BR /> Thu, 22 Nov 2007 12:40:55 GMT https://community.intel.com/t5/Intel-Moderncode-for-Parallel/matrix-multiplication/m-p/889936#M3744 ashoksaravanan 2007-11-22T12:40:55Z