Measure Performance of dgemm

Use the dsecnd routine to return the elapsed CPU time in seconds.

*      Fortran source code is found in dgemm_with_timing.f

      PRINT *, "Making the first run of matrix product using "
      PRINT *, "Intel(R) MKL DGEMM subroutine to get stable "
      PRINT *, "run time measurements"
      PRINT *, ""
      CALL DGEMM('N','N',M,N,K,ALPHA,A,M,B,K,BETA,C,M)

      PRINT *, "Measuring performance of matrix product using "
      PRINT *, "Intel(R) MKL DGEMM subroutine"
      PRINT *, ""
      S_INITIAL = DSECND()
      DO R = 1, LOOP_COUNT
        CALL DGEMM('N','N',M,N,K,ALPHA,A,M,B,K,BETA,C,M)
      END DO
      S_ELAPSED = (DSECND() - S_INITIAL) / LOOP_COUNT
      PRINT *, "== Matrix multiplication using Intel(R) MKL DGEMM =="
      PRINT 50, " == completed at ",S_ELAPSED*1000," milliseconds =="
 50   FORMAT(A,F12.5,A)
      PRINT *, ""

Measure Performance Without Using dgemm

In order to show the improvement resulting from using dgemm, perform the same measurement, but use a triply-nested loop to multiply the matrices.

*       Fortran source code is found in matrix_multiplication.f

      PRINT *, "Making the first run of matrix product using "
      PRINT *, "triple nested loop to get stable run time"
      PRINT *, "measurements"
      PRINT *, ""
      DO I = 1, M
        DO J = 1, N
          TEMP = 0.0
          DO L = 1, K
            TEMP = TEMP + A(I,L) * B(L,J) 
          END DO
          C(I,J) = TEMP
        END DO
      END DO
      
      PRINT *, "Measuring performance of matrix product using "
      PRINT *, "triple nested loop"
      PRINT *, ""
      S_INITIAL = DSECND()
      DO R = 1, LOOP_COUNT
        DO I = 1, M
          DO J = 1, N
            TEMP = 0.0
            DO L = 1, K
              TEMP = TEMP + A(I,L) * B(L,J) 
            END DO
            C(I,J) = TEMP
          END DO
        END DO
      END DO
      S_ELAPSED = (DSECND() - S_INITIAL) / LOOP_COUNT
      PRINT *, "== Matrix multiplication using triple nested loop =="
      PRINT 50, " == completed at ",S_ELAPSED*1000," milliseconds =="
 50   FORMAT(A,F12.5,A)
      PRINT *, ""
 

Compare the results in the first exercise using dgemm to the results of the second exercise without using dgemm.

You can find more information about measuring oneMKL performance from the article "A simple example to measure the performance of an oneMKL function" in the Intel® oneAPI Math Kernel Library Knowledge Base.