了解#pragma acc 内核

Question

我正在尝试优化 nbody 算法，当我在循环中添加 #pragma acc kernels 时，我不明白以下注释是什么

#pragma acc kernels
  for (i = 0; i < n; i++)
  {
    real fx, fy, fz;
    fx = fy = fz = 0;

    real iPosx = in[i].x;
    real iPosy = in[i].y;
    real iPosz = in[i].z;

    for (j = 0; j < n; j++)
    {   
      real rx, ry, rz;

      rx = in[j].x - iPosx;
      ry = in[j].y - iPosy;
      rz = in[j].z - iPosz;

      real distSqr = rx*rx+ry*ry+rz*rz;
      distSqr += SOFTENING_SQUARED;

      real s = in[j].w / POW(distSqr,1.5);

      real3 ff;
      ff.x = rx * s;
      ff.y = ry * s;
      ff.z = rz * s;

      fx += ff.x;
      fy += ff.y;
      fz += ff.z;
    }

    force[i].x = fx;
    force[i].y = fy;
    force[i].z = fz;
  }

“生成隐式缩减(+:fx)”是什么意思

"生成隐式缩减(+:fy)

"generating implicit reduction(+:fz)"?

谢谢

Answer 1

为了并行化内部 "j" 循环，三个变量 fx、fy 和 fz 必须在总和缩减中。编译器已自动检测到这一点，因此隐式地为您添加了缩减。这与您明确声明它们一样，例如：

#pragma acc loop reduction(+:fx,fy,fz)
 for (j = 0; j < n; j++)
{   
  real rx, ry, rz;

了解#pragma acc 内核

Understanding #pragma acc kernels

c

optimization

openacc