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https://github.com/Steffo99/unimore-hpc-assignments.git
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128 lines
2.7 KiB
C
128 lines
2.7 KiB
C
/**
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* @file saxpy.c
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*
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* @brief saxpy performs the \c axpy computation in single-precision on both
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* host and accelerator. The performance (in MFLOPS) on host and accelerator is
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* compared and the numerical results are also verified for consistency.
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*
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* The \c axpy computation is defined as:
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*
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* y := a * x + y
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*
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* where:
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*
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* - a is a scalar.
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* - x and y are vectors each with n elements.
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*
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* Please note that in this version only <em>one GPU thread</em> is used.
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*
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* Offload to GPU:
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*
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* gcc -fopenmp -foffload=nvptx-none saxpy.c
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*
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*/
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#include <assert.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <time.h>
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#include <omp.h>
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#include "utils.h"
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#define TWO02 (1 << 2)
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#define TWO04 (1 << 4)
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#define TWO08 (1 << 8)
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#ifndef N
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#define N (1 << 27)
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#endif
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int main(int argc, char *argv[])
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{
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int i, n = N,
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iret = 0;
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float a = 101.0f / TWO02,
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b, c,
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*x, *y, *z;
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struct timespec rt[2];
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double wt; // walltime
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if (argc > 1)
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n = atoi(argv[1]);
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/*
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* 0. prepare x, y, and z
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*
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* y := a * x + y (on host)
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* z := a * x + z (on accel)
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*/
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if (NULL == (x = (float *)malloc(sizeof(*x) * n)))
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{
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printf("error: memory allocation for 'x'\n");
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iret = -1;
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}
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if (NULL == (y = (float *)malloc(sizeof(*y) * n)))
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{
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printf("error: memory allocation for 'y'\n");
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iret = -1;
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}
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if (NULL == (z = (float *)malloc(sizeof(*z) * n)))
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{
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printf("error: memory allocation for 'z'\n");
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iret = -1;
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}
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if (0 != iret)
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{
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free(x);
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free(y);
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free(z);
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exit(EXIT_FAILURE);
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}
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b = rand() % TWO04;
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c = rand() % TWO08;
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for (i = 0; i < n; i++)
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{
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x[i] = b / (float)TWO02;
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y[i] = z[i] = c / (float)TWO04;
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}
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/*
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* 1. saxpy on host
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*/
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clock_gettime(CLOCK_REALTIME, rt + 0);
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for (i = 0; i < n; i++)
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{
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y[i] = a * x[i] + y[i];
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}
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clock_gettime(CLOCK_REALTIME, rt + 1);
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wt = (rt[1].tv_sec - rt[0].tv_sec) + 1.0e-9 * (rt[1].tv_nsec - rt[0].tv_nsec);
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printf("saxpy on host : %9.3f sec %9.1f MFLOPS\n", wt, 2.0 * n / (1.0e6 * wt));
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/*
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* 2. saxpy on accel
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*/
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clock_gettime(CLOCK_REALTIME, rt + 0);
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int BLOCK=n/8;
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for (int i = 0; i < n; i+=BLOCK)
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{
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#pragma omp target teams distribute parallel for map(to: a, x [i:BLOCK]) map(tofrom: z [i:BLOCK]) nowait
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for (int ii = 0; ii < BLOCK; ii++)
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{
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z[i+ii] = a * x[i+ii] + z[i+ii];
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}
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}
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#pragma omp taskwait
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clock_gettime(CLOCK_REALTIME, rt + 1);
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wt = (rt[1].tv_sec - rt[0].tv_sec) + 1.0e-9 * (rt[1].tv_nsec - rt[0].tv_nsec);
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printf("saxpy on accel: %9.3f sec %9.1f MFLOPS\n", wt, 2.0 * n / (1.0e6 * wt));
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/*
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* 3. verify numerical consistency
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*/
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for (i = 0; i < n; i++)
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{
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iret = *(int *)(y + i) ^ *(int *)(z + i);
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assert(iret == 0);
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}
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return 0;
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}
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