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| real cpu_reduction (GLuint src, size_t offset, size_t nb, const char op)
{
GL_C (glBindBuffer (GL_SHADER_STORAGE_BUFFER, src));
GL_C (glMemoryBarrier (GL_BUFFER_UPDATE_BARRIER_BIT));
real result = 0., * a = glMapBufferRange (GL_SHADER_STORAGE_BUFFER,
offset*sizeof(real), nb*sizeof(real),
GL_MAP_READ_BIT);
assert (a);
switch (op) {
case '+':
for (int i = 0; i < nb; i++, a++)
result += *a;
break;
case 'M':
result = *a++;
for (int i = 1; i < nb; i++, a++)
result = max (result, *a);
break;
case 'm':
result = *a++;
for (int i = 1; i < nb; i++, a++)
result = min (result, *a);
break;
default: assert (false);
}
assert (glUnmapBuffer (GL_SHADER_STORAGE_BUFFER));
GL_C (glBindBuffer (GL_SHADER_STORAGE_BUFFER, 0));
return result;
}
real gpu_reduction (size_t offset, const char op, const RegionParameters * region, size_t nb)
{
const int stride = 64, nwgr = 64;
bool is_foreach_point = (region->n.x == 1 && region->n.y == 1);
if (!is_foreach_point && nb < nwgr*stride)
return cpu_reduction (GPUContext.ssbo, offset, nb, op);
GLuint * br = gpu_grid->reduct;
if (!br[0]) {
GL_C (glGenBuffers (2, br));
for (int i = 0; i < 2; i++) {
GL_C (glBindBuffer (GL_SHADER_STORAGE_BUFFER, br[i]));
GL_C (glBufferData (GL_SHADER_STORAGE_BUFFER,
(sq(N + 1)/stride + 1)*sizeof(real),
NULL, GL_DYNAMIC_READ));
}
GL_C (glBindBuffer (GL_SHADER_STORAGE_BUFFER, 0));
}
const char * start, * operation;
static const char * startsum = "reduct = 0.;",
* opsum = "reduct += val;";
static const char * startmin = "reduct = val;",
* opmin = "if (val < reduct) reduct = val;";
static const char * startmax = "reduct = val;",
* opmax = "if (val > reduct) reduct = val;";
switch (op) {
case '+': start = startsum, operation = opsum; break;
case 'M': start = startmax, operation = opmax; break;
case 'm': start = startmin, operation = opmin; break;
default: // unknown reduction operation
assert (false);
}
char nwgrs[20], strides[20];
snprintf (nwgrs, 19, "%d", nwgr);
snprintf (strides, 19, "%d", stride);
char * fs =
str_append (NULL,
"#version 430\n", glsl_preproc,
"layout (std430, binding = 0) readonly buffer _data_layout {"
" real _data[]; };\n"
"layout (std430, binding = 1) writeonly buffer _reduct_layout {"
" real _reduct[]; };\n"
"layout (location = 3) uniform uint offset;\n"
"layout (location = 4) uniform uint nb;\n"
"layout (location = 5) uniform uint nbr;\n"
"layout (local_size_x = ", nwgrs, ") in;\n"
"void main() {\n"
"if (gl_GlobalInvocationID.x < nb) {\n"
" uint stride = ", strides, ";\n"
" uint index = stride*gl_GlobalInvocationID.x;\n"
" if (index + stride > nbr) stride = nbr - index;\n"
" index += offset;\n"
" real val = _data[index];\n"
" real ", start, "\n"
" for (uint j = 0; j < stride; j++) {\n"
" val = _data[index + j];\n"
" ", operation, "\n"
" }\n"
" _reduct[gl_GlobalInvocationID.x] = reduct;\n"
"}}\n");
Shader * shader;
Adler32Hash hash;
a32_hash_init (&hash);
a32_hash_add (&hash, fs, strlen (fs));
shader = load_shader (fs, a32_hash (&hash), NULL);
assert (shader);
GL_C (glUseProgram (shader->id));
const GLint loffset = 3, lnb = 4, lnbr = 5;
if (is_foreach_point) {
real result = 0.;
int i = (region->p.x - X0)/L0*N;
int j = (region->p.y - Y0)/L0*N;
if (i >= 0 && i < N && j >= 0 && j < N) {
offset += i*N + j;
GL_C (glUniform1ui (loffset, offset));
GL_C (glBindBufferBase (GL_SHADER_STORAGE_BUFFER, 0, GPUContext.ssbo));
GL_C (glBindBufferBase (GL_SHADER_STORAGE_BUFFER, 1, br[0]));
GL_C (glUniform1ui (lnbr, 1));
GL_C (glUniform1ui (lnb, 1));
GL_C (glMemoryBarrier (GL_SHADER_STORAGE_BARRIER_BIT));
GL_C (glDispatchCompute (1, 1, 1));
GL_C (glBindBuffer (GL_SHADER_STORAGE_BUFFER, br[0]));
GL_C (glGetBufferSubData (GL_SHADER_STORAGE_BUFFER, 0, sizeof (real), &result));
GL_C (glBindBuffer (GL_SHADER_STORAGE_BUFFER, 0));
}
return result;
}
GL_C (glUniform1ui (loffset, offset));
GL_C (glBindBufferBase (GL_SHADER_STORAGE_BUFFER, 0, GPUContext.ssbo));
int src = 0, dst = 1;
while (nb >= nwgr*stride) {
GL_C (glBindBufferBase (GL_SHADER_STORAGE_BUFFER, 1, br[dst]));
GL_C (glUniform1ui (lnbr, nb));
if (nb % stride) {
nb /= stride;
nb++;
}
else
nb /= stride;
int ng = nb/nwgr;
if (ng*nwgr < nb)
ng++;
GL_C (glUniform1ui (lnb, nb));
GL_C (glMemoryBarrier (GL_SHADER_STORAGE_BARRIER_BIT));
GL_C (glDispatchCompute (ng, 1, 1));
swap (int, src, dst);
if (offset) {
GL_C (glUniform1ui (loffset, 0));
offset = 0;
}
GL_C (glBindBufferBase (GL_SHADER_STORAGE_BUFFER, 0, br[src]));
}
return cpu_reduction (br[src], 0, nb, op);
}
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