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// =================================================================================================
// This file is part of the CLBlast project. The project is licensed under Apache Version 2.0. This
// project loosely follows the Google C++ styleguide and uses a tab-size of two spaces and a max-
// width of 100 characters per line.
//
// Author(s):
// Cedric Nugteren <www.cedricnugteren.nl>
//
// This file contains the Xdot kernel. It implements a dot-product computation using reduction
// kernels. Reduction is split in two parts. In the first (main) kernel the X and Y vectors are
// multiplied, followed by a per-thread and a per-workgroup reduction. The second (epilogue) kernel
// is executed with a single workgroup only, computing the final result.
//
// =================================================================================================
// Enables loading of this file using the C++ pre-processor's #include (C++11 standard raw string
// literal). Comment-out this line for syntax-highlighting when developing.
R"(
// Parameters set by the tuner or by the database. Here they are given a basic default value in case
// this kernel file is used outside of the CLBlast library.
#ifndef WGS1
#define WGS1 64 // The local work-group size of the main kernel
#endif
#ifndef WGS2
#define WGS2 64 // The local work-group size of the epilogue kernel
#endif
// =================================================================================================
// The main reduction kernel, performing the multiplication and the majority of the sum operation
#if RELAX_WORKGROUP_SIZE == 1
__kernel
#else
__kernel __attribute__((reqd_work_group_size(WGS1, 1, 1)))
#endif
void Xdot(const int n,
const __global real* restrict xgm, const int x_offset, const int x_inc,
const __global real* restrict ygm, const int y_offset, const int y_inc,
__global real* output, const int do_conjugate) {
__local real lm[WGS1];
const int lid = get_local_id(0);
const int wgid = get_group_id(0);
const int num_groups = get_num_groups(0);
// Performs multiplication and the first steps of the reduction
real acc;
SetToZero(acc);
int id = wgid*WGS1 + lid;
while (id < n) {
real x = xgm[id*x_inc + x_offset];
real y = ygm[id*y_inc + y_offset];
if (do_conjugate) { COMPLEX_CONJUGATE(x); }
MultiplyAdd(acc, x, y);
id += WGS1*num_groups;
}
lm[lid] = acc;
barrier(CLK_LOCAL_MEM_FENCE);
// Performs reduction in local memory
for (int s=WGS1/2; s>0; s=s>>1) {
if (lid < s) {
Add(lm[lid], lm[lid], lm[lid + s]);
}
barrier(CLK_LOCAL_MEM_FENCE);
}
// Stores the per-workgroup result
if (lid == 0) {
output[wgid] = lm[0];
}
}
// =================================================================================================
// The epilogue reduction kernel, performing the final bit of the sum operation. This kernel has to
// be launched with a single workgroup only.
#if RELAX_WORKGROUP_SIZE == 1
__kernel
#else
__kernel __attribute__((reqd_work_group_size(WGS2, 1, 1)))
#endif
void XdotEpilogue(const __global real* restrict input,
__global real* dot, const int dot_offset) {
__local real lm[WGS2];
const int lid = get_local_id(0);
// Performs the first step of the reduction while loading the data
Add(lm[lid], input[lid], input[lid + WGS2]);
barrier(CLK_LOCAL_MEM_FENCE);
// Performs reduction in local memory
for (int s=WGS2/2; s>0; s=s>>1) {
if (lid < s) {
Add(lm[lid], lm[lid], lm[lid + s]);
}
barrier(CLK_LOCAL_MEM_FENCE);
}
// Stores the final result
if (lid == 0) {
dot[dot_offset] = lm[0];
}
}
// =================================================================================================
// End of the C++11 raw string literal
)"
// =================================================================================================
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