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C++ AMPを使用して並列計算用のアルゴリズム（Lattice Boltmann）を最適化しようとしています。また、メモリレイアウトを最適化するための提案を探して、構造から別のベクター（ブロックされたベクター）に1つのパラメータを削除すると約10％の増加となりました。並列計算用のメモリレイアウトを改善する
これ以上改善できるヒントがあれば誰でも気になるはずです。 以下は、タイムステップごとに実行される最も時間のかかる機能と、レイアウトに使用される構造です。
struct grid_cell {
// int blocked; // Define if blocked
float n; // North
float ne; // North-East
float e; // East
float se; // South-East
float s;
float sw;
float w;
float nw;
float c; // Center
};
int collision(const struct st_parameters param, vector<struct grid_cell> &node, vector<struct grid_cell> &tmp_node, vector<int> &obstacle) {
int x,y;
int i = 0;
float c_sq = 1.0f/3.0f; // Square of speed of sound
float w0 = 4.0f/9.0f; // Weighting factors
float w1 = 1.0f/9.0f;
float w2 = 1.0f/36.0f;
int chunk = param.ny/20;
float total_density = 0;
float u_x,u_y; // Avrage velocities in x and y direction
float u[9]; // Directional velocities
float d_equ[9]; // Equalibrium densities
float u_sq; // Squared velocity
float local_density; // Sum of densities in a particular node
for(y=0;y<param.ny;y++) {
for(x=0;x<param.nx;x++) {
i = y*param.nx + x; // Node index
// Dont consider blocked cells
if (obstacle[i] == 0) {
// Calculate local density
local_density = 0.0;
local_density += tmp_node[i].n;
local_density += tmp_node[i].e;
local_density += tmp_node[i].s;
local_density += tmp_node[i].w;
local_density += tmp_node[i].ne;
local_density += tmp_node[i].se;
local_density += tmp_node[i].sw;
local_density += tmp_node[i].nw;
local_density += tmp_node[i].c;
// Calculate x velocity component
u_x = (tmp_node[i].e + tmp_node[i].ne + tmp_node[i].se -
(tmp_node[i].w + tmp_node[i].nw + tmp_node[i].sw))
/local_density;
// Calculate y velocity component
u_y = (tmp_node[i].n + tmp_node[i].ne + tmp_node[i].nw -
(tmp_node[i].s + tmp_node[i].sw + tmp_node[i].se))
/local_density;
// Velocity squared
u_sq = u_x*u_x +u_y*u_y;
// Directional velocity components;
u[1] = u_x; // East
u[2] = u_y; // North
u[3] = -u_x; // West
u[4] = - u_y; // South
u[5] = u_x + u_y; // North-East
u[6] = -u_x + u_y; // North-West
u[7] = -u_x - u_y; // South-West
u[8] = u_x - u_y; // South-East
// Equalibrium densities
// Zero velocity density: weight w0
d_equ[0] = w0 * local_density * (1.0f - u_sq/(2.0f * c_sq));
// Axis speeds: weight w1
d_equ[1] = w1 * local_density * (1.0f + u[1]/c_sq
+ (u[1] * u[1])/(2.0f * c_sq * c_sq)
- u_sq/(2.0f * c_sq));
d_equ[2] = w1 * local_density * (1.0f + u[2]/c_sq
+ (u[2] * u[2])/(2.0f * c_sq * c_sq)
- u_sq/(2.0f * c_sq));
d_equ[3] = w1 * local_density * (1.0f + u[3]/c_sq
+ (u[3] * u[3])/(2.0f * c_sq * c_sq)
- u_sq/(2.0f * c_sq));
d_equ[4] = w1 * local_density * (1.0f + u[4]/c_sq
+ (u[4] * u[4])/(2.0f * c_sq * c_sq)
- u_sq/(2.0f * c_sq));
// Diagonal speeds: weight w2
d_equ[5] = w2 * local_density * (1.0f + u[5]/c_sq
+ (u[5] * u[5])/(2.0f * c_sq * c_sq)
- u_sq/(2.0f * c_sq));
d_equ[6] = w2 * local_density * (1.0f + u[6]/c_sq
+ (u[6] * u[6])/(2.0f * c_sq * c_sq)
- u_sq/(2.0f * c_sq));
d_equ[7] = w2 * local_density * (1.0f + u[7]/c_sq
+ (u[7] * u[7])/(2.0f * c_sq * c_sq)
- u_sq/(2.0f * c_sq));
d_equ[8] = w2 * local_density * (1.0f + u[8]/c_sq
+ (u[8] * u[8])/(2.0f * c_sq * c_sq)
- u_sq/(2.0f * c_sq));
// Relaxation step
node[i].c = (tmp_node[i].c + param.omega * (d_equ[0] - tmp_node[i].c));
node[i].e = (tmp_node[i].e + param.omega * (d_equ[1] - tmp_node[i].e));
node[i].n = (tmp_node[i].n + param.omega * (d_equ[2] - tmp_node[i].n));
node[i].w = (tmp_node[i].w + param.omega * (d_equ[3] - tmp_node[i].w));
node[i].s = (tmp_node[i].s + param.omega * (d_equ[4] - tmp_node[i].s));
node[i].ne = (tmp_node[i].ne + param.omega * (d_equ[5] - tmp_node[i].ne));
node[i].nw = (tmp_node[i].nw + param.omega * (d_equ[6] - tmp_node[i].nw));
node[i].sw = (tmp_node[i].sw + param.omega * (d_equ[7] - tmp_node[i].sw));
node[i].se = (tmp_node[i].se + param.omega * (d_equ[8] - tmp_node[i].se));
}
}
}
return 1;
}