SIMD and Others

In this exercise, we will try to add the simd classes to our existing problems, for example, vector addition.

Examples and Question: SIMD - Vector Addition

Serial(C/C++)Serial(FORTRAN)Template(C/C++)Template(FORTRAN)Solution(C/C++)Solution(FORTRAN)

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <assert.h>
#include <time.h>

#define N 5120
#define MAX_ERR 1e-6

// CPU function that adds two vector 
float * Vector_Add(float *a, float *b, float *c, int n) 
{
  for(int i = 0; i < n; i ++)
    {
      c[i] = a[i] + b[i];
    }
  return c;
}

int main()
{
  // Initialize the variables
  float *a, *b, *c;       

  // Allocate the memory
  a   = (float*)malloc(sizeof(float) * N);
  b   = (float*)malloc(sizeof(float) * N);
  c = (float*)malloc(sizeof(float) * N);

  // Initialize the arrays
  for(int i = 0; i < N; i++)
    {
      a[i] = 1.0f;
      b[i] = 2.0f;
    }

  // Start measuring time
  clock_t start = clock();

  // Executing vector addition function 
  Vector_Add(a, b, c, N);

  // Stop measuring time and calculate the elapsed time
  clock_t end = clock();
  double elapsed = (double)(end - start)/CLOCKS_PER_SEC;

  printf("Time measured: %.3f seconds.\n", elapsed);

  // Verification
  for(int i = 0; i < N; i++)
    {
      assert(fabs(c[i] - a[i] - b[i]) < MAX_ERR);
    }

  printf("c[0] = %f\n", c[0]);
  printf("PASSED\n");

  // Deallocate the memory
  free(a); 
  free(b); 
  free(c);

  return 0;
}

module Vector_Addition_Mod  
implicit none 
  contains
subroutine Vector_Addition(a, b, c, n)
! Input vectors
real(8), intent(in), dimension(:) :: a
real(8), intent(in), dimension(:) :: b
real(8), intent(out), dimension(:) :: c
integer :: i, n
  do i = 1, n
    c(i) = a(i) + b(i)
  end do
 end subroutine Vector_Addition
end module Vector_Addition_Mod

program main
use Vector_Addition_Mod
implicit none
! Input vectors
real(8), dimension(:), allocatable :: a
real(8), dimension(:), allocatable :: b 
! Output vector
real(8), dimension(:), allocatable :: c
! real(8) :: sum = 0

integer :: n, i  
print *, "This program does the addition of two vectors "
print *, "Please specify the vector size = "
read *, n

! Allocate memory for vector
allocate(a(n))
allocate(b(n))
allocate(c(n))

! Initialize content of input vectors, 
! vector a[i] = sin(i)^2 vector b[i] = cos(i)^2
do i = 1, n
  a(i) = sin(i*1D0) * sin(i*1D0)
  b(i) = cos(i*1D0) * cos(i*1D0) 
enddo

! Call the vector addition subroutine 
call Vector_Addition(a, b, c, n)

!!Verification
do i = 1, n
  if (abs(c(i)-(a(i)+b(i)) == 0.00000)) then 
   else
     print *, "FAIL"
   endif
enddo
print *, "PASS"

! Delete the memory
deallocate(a)
deallocate(b)
deallocate(c)

end program main

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <assert.h>
#include <time.h>
#include <omp.h>

#define N 5120
#define MAX_ERR 1e-6

// CPU function that adds two vector 
float * Vector_Add(float *a, float *b, float *c, int n) 
{
// ADD YOUR PARALLEL REGION FOR THE LOOP SIMD
  for(int i = 0; i < n; i ++)
    {
      c[i] = a[i] + b[i];
    }
  return c;
}

int main()
{
  // Initialize the variables
  float *a, *b, *c;       

  // Allocate the memory
  a   = (float*)malloc(sizeof(float) * N);
  b   = (float*)malloc(sizeof(float) * N);
  c = (float*)malloc(sizeof(float) * N);

  // Initialize the arrays
  for(int i = 0; i < N; i++)
    {
      a[i] = 1.0f;
      b[i] = 2.0f;
    }

  // Start measuring time
  clock_t start = clock();

  // ADD YOUR PARALLEL REGION HERE  
  // Executing vector addition function 
  Vector_Add(a, b, c, N);

  // Stop measuring time and calculate the elapsed time
  clock_t end = clock();
  double elapsed = (double)(end - start)/CLOCKS_PER_SEC;

  printf("Time measured: %.3f seconds.\n", elapsed);

  // Verification
  for(int i = 0; i < N; i++)
    {
      assert(fabs(c[i] - a[i] - b[i]) < MAX_ERR);
    }

  printf("c[0] = %f\n", c[0]);
  printf("PASSED\n");

  // Deallocate the memory
  free(a); 
  free(b); 
  free(c);

  return 0;
}

module Vector_Addition_Mod  
implicit none 
  contains
subroutine Vector_Addition(a, b, c, n)
use omp_lib
! Input vectors
real(8), intent(in), dimension(:) :: a
real(8), intent(in), dimension(:) :: b
real(8), intent(out), dimension(:) :: c
integer :: i, n
!! ADD YOUR PARALLEL DO LOOP WITH SIMD
  do i = 1, n
    c(i) = a(i) + b(i)
  end do
 end subroutine Vector_Addition
end module Vector_Addition_Mod

program main
use Vector_Addition_Mod
implicit none
! Input vectors
real(8), dimension(:), allocatable :: a
real(8), dimension(:), allocatable :: b 
! Output vector
real(8), dimension(:), allocatable :: c
! real(8) :: sum = 0

integer :: n, i  
print *, "This program does the addition of two vectors "
print *, "Please specify the vector size = "
read *, n

! Allocate memory for vector
allocate(a(n))
allocate(b(n))
allocate(c(n))

! Initialize content of input vectors, 
! vector a[i] = sin(i)^2 vector b[i] = cos(i)^2
do i = 1, n
  a(i) = sin(i*1D0) * sin(i*1D0)
  b(i) = cos(i*1D0) * cos(i*1D0) 
enddo

!! ADD YOUR PARALLEL REGION 
! Call the vector add subroutine 
call Vector_Addition(a, b, c, n)

!!Verification
do i = 1, n
  if (abs(c(i)-(a(i)+b(i)) == 0.00000)) then 
   else
     print *, "FAIL"
   endif
enddo
print *, "PASS"

! Delete the memory
deallocate(a)
deallocate(b)
deallocate(c)

end program main

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <assert.h>
#include <time.h>
#include <omp.h>

#define N 5120
#define MAX_ERR 1e-6

// CPU function that adds two vector 
float * Vector_Add(float *a, float *b, float *c, int n) 
{
// ADD YOUR PARALLEL SIMD
#pragma omp for simd
  for(int i = 0; i < n; i ++)
    {
      c[i] = a[i] + b[i];
    }
  return c;
}

int main()
{
  // Initialize the variables
  float *a, *b, *c;       

  // Allocate the memory
  a   = (float*)malloc(sizeof(float) * N);
  b   = (float*)malloc(sizeof(float) * N);
  c = (float*)malloc(sizeof(float) * N);

  // Initialize the arrays
  for(int i = 0; i < N; i++)
    {
      a[i] = 1.0f;
      b[i] = 2.0f;
    }

  double start = omp_get_wtime();
  #pragma omp parallel 
  // Executing vector addition function 
  Vector_Add(a, b, c, N);
  double end = omp_get_wtime();
  printf("Work took %f seconds\n", end - start);

  // Verification
  for(int i = 0; i < N; i++)
    {
      assert(fabs(c[i] - a[i] - b[i]) < MAX_ERR);
    }

  printf("c[0] = %f\n", c[0]);
  printf("PASSED\n");

  // Deallocate the memory
  free(a); 
  free(b); 
  free(c);

  return 0;
}

module Vector_Addition_Mod  
implicit none 
  contains
subroutine Vector_Addition(a, b, c, n)
use omp_lib
! Input vectors
real(8), intent(in), dimension(:) :: a
real(8), intent(in), dimension(:) :: b
real(8), intent(out), dimension(:) :: c
integer :: i, n
!$omp do simd
  do i = 1, n
    c(i) = a(i) + b(i)
  end do
!$omp end do simd
 end subroutine Vector_Addition
end module Vector_Addition_Mod

program main
use Vector_Addition_Mod
implicit none
! Input vectors
real(8), dimension(:), allocatable :: a
real(8), dimension(:), allocatable :: b 
! Output vector
real(8), dimension(:), allocatable :: c
! real(8) :: sum = 0
double precision :: start, end

integer :: n, i  
print *, "This program does the addition of two vectors "
print *, "Please specify the vector size = "
read *, n

! Allocate memory for vector
allocate(a(n))
allocate(b(n))
allocate(c(n))

! Initialize content of input vectors, 
! vector a[i] = sin(i)^2 vector b[i] = cos(i)^2
do i = 1, n
  a(i) = sin(i*1D0) * sin(i*1D0)
  b(i) = cos(i*1D0) * cos(i*1D0) 
enddo

start = omp_get_wtime()
!$omp parallel 
! Call the vector addition subroutine 
call Vector_Addition(a, b, c, n)
!$omp end parallel
end = omp_get_wtime()
PRINT *, "Work took", end - start, "seconds"

!!Verification
do i = 1, n
  if (abs(c(i)-(a(i)+b(i)) == 0.00000)) then 
   else
     print *, "FAIL"
   endif
enddo
print *, "PASS"

! Delete the memory
deallocate(a)
deallocate(b)
deallocate(c)

end program main

Please try the examples without the simd clause. Do you notice any performance differences?

Critical, Single, and Master¶

We will explore how single, master and critical are working in the OpenMP programming model. For this, we consider the following simple examples.

Examples and Question: Critical, Single and Master

(C/C++)FORTRAN)

#include<iostream>
#include<omp.h>
#include <omp.h>
using namespace std;
int main()
{
  cout << "Hello world from the master thread "<< endl;
  cout << endl;

  // creating the parallel region (with N number of threads)
  #pragma omp parallel
   {
        cout << "Hello world from thread id "
        << omp_get_thread_num() << " from the team size of "
        << omp_get_num_threads()
        << endl;
    } // parallel region is closed

cout << endl;
cout << "end of the programme from the master thread" << endl;
return 0;
}

program Hello_world_OpenMP
use omp_lib

!$omp parallel 
print *, 'Hello world from thread id ', omp_get_thread_num(), 'from the team size of', omp_get_num_threads()
!$omp end parallel

end program

Try single clause
Try master clause
Try critical clause