The dot_product example computes the scalar product of two vectors by the means

of a reduction.

examples/Makefile.am

@@ -574,3 +574,16 @@ examplebin_PROGRAMS +=				\
 
 scheduler_dummy_sched_SOURCES =			\
 	scheduler/dummy_sched.c
+
+#######################
+# dot_product example #
+#######################
+
+check_PROGRAMS +=				\
+	dot_product/dot_product
+
+examplebin_PROGRAMS +=				\
+	dot_product/dot_product
+
+dot_product_dot_product_SOURCES =		\
+	dot_product/dot_product.c

examples/dot_product/dot_product.c

@@ -0,0 +1,220 @@
+/*
+ * StarPU
+ * Copyright (C) Université Bordeaux 1, CNRS 2008-2010 (see AUTHORS file)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 of the License, or (at
+ * your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * See the GNU Lesser General Public License in COPYING.LGPL for more details.
+ */
+
+#include <starpu.h>
+#include <assert.h>
+
+#include <cuda.h>
+#include <cublas.h>
+
+static float *x;
+static float *y;
+static starpu_data_handle *x_handles;
+static starpu_data_handle *y_handles;
+
+static unsigned nblocks = 4096;
+static unsigned entries_per_bock = 1024;
+
+#define DOT_TYPE double
+
+static DOT_TYPE dot = 0.0f;
+static starpu_data_handle dot_handle;
+
+/*
+ *	Codelet to create a neutral element
+ */
+
+void init_cpu_func(void *descr[], void *cl_arg)
+{
+	DOT_TYPE *dot = (DOT_TYPE *)STARPU_VARIABLE_GET_PTR(descr[0]);
+	*dot = 0.0f;
+}
+
+void init_cuda_func(void *descr[], void *cl_arg)
+{
+	DOT_TYPE *dot = (DOT_TYPE *)STARPU_VARIABLE_GET_PTR(descr[0]);
+	cudaMemset(dot, 0, sizeof(DOT_TYPE));
+	cudaThreadSynchronize();
+}
+
+static struct starpu_codelet_t init_codelet = {
+	.where = STARPU_CPU|STARPU_CUDA,
+	.cpu_func = init_cpu_func,
+	.cuda_func = init_cuda_func,
+	.nbuffers = 1
+};
+
+/*
+ *	Codelet to perform the reduction of two elements
+ */
+
+void redux_cpu_func(void *descr[], void *cl_arg)
+{
+	DOT_TYPE *dota = (DOT_TYPE *)STARPU_VARIABLE_GET_PTR(descr[0]);
+	DOT_TYPE *dotb = (DOT_TYPE *)STARPU_VARIABLE_GET_PTR(descr[1]);
+
+	*dota = *dota + *dotb;
+}
+
+static struct starpu_codelet_t redux_codelet = {
+	.where = STARPU_CPU,
+	.cpu_func = redux_cpu_func,
+	.nbuffers = 2
+};
+
+/*
+ *	Dot product codelet
+ */
+
+void dot_cpu_func(void *descr[], void *cl_arg)
+{
+	float *local_x = (float *)STARPU_VECTOR_GET_PTR(descr[0]);
+	float *local_y = (float *)STARPU_VECTOR_GET_PTR(descr[1]);
+	DOT_TYPE *dot = (DOT_TYPE *)STARPU_VARIABLE_GET_PTR(descr[2]);
+
+	unsigned n = STARPU_VECTOR_GET_NX(descr[0]);
+
+	DOT_TYPE local_dot = 0.0;
+
+	unsigned i;
+	for (i = 0; i < n; i++)
+	{
+		local_dot += (DOT_TYPE)local_x[i]*(DOT_TYPE)local_y[i];
+	}
+
+	*dot = *dot + local_dot;
+}
+
+void dot_cuda_func(void *descr[], void *cl_arg)
+{
+	DOT_TYPE current_dot;
+	DOT_TYPE local_dot;
+
+	float *local_x = (float *)STARPU_VECTOR_GET_PTR(descr[0]);
+	float *local_y = (float *)STARPU_VECTOR_GET_PTR(descr[1]);
+	DOT_TYPE *dot = (DOT_TYPE *)STARPU_VARIABLE_GET_PTR(descr[2]);
+
+	unsigned n = STARPU_VECTOR_GET_NX(descr[0]);
+
+	cudaMemcpy(&current_dot, dot, sizeof(DOT_TYPE), cudaMemcpyDeviceToHost);
+
+	int ret = cudaThreadSynchronize();
+
+	local_dot = (DOT_TYPE)cublasSdot(n, local_x, 1, local_y, 1);
+
+	//fprintf(stderr, "current_dot %f local dot %f -> %f\n", current_dot, local_dot, current_dot + local_dot);
+	current_dot += local_dot;
+
+	cudaThreadSynchronize();
+
+	cudaMemcpy(dot, &current_dot, sizeof(DOT_TYPE), cudaMemcpyHostToDevice);
+
+	cudaThreadSynchronize();
+}
+
+static struct starpu_codelet_t dot_codelet = {
+	.where = STARPU_CPU|STARPU_CUDA,
+	.cpu_func = dot_cpu_func,
+	.cuda_func = dot_cuda_func,
+	.nbuffers = 3
+};
+
+/*
+ *	Tasks initialization
+ */
+
+extern void starpu_data_start_reduction_mode(starpu_data_handle handle);
+extern void starpu_data_end_reduction_mode(starpu_data_handle handle);
+
+int main(int argc, char **argv)
+{
+	starpu_init(NULL);
+
+	starpu_helper_cublas_init();
+
+	unsigned long nelems = nblocks*entries_per_bock;
+	size_t size = nelems*sizeof(float);
+
+	x = malloc(size);
+	y = malloc(size);
+
+	x_handles = calloc(nblocks, sizeof(starpu_data_handle));
+	y_handles = calloc(nblocks, sizeof(starpu_data_handle));
+
+	assert(x && y);
+
+        starpu_srand48(0);
+	
+	DOT_TYPE reference_dot = 0.0;
+
+	unsigned long i;
+	for (i = 0; i < nelems; i++)
+	{
+		x[i] = (float)starpu_drand48();
+		y[i] = (float)starpu_drand48();
+
+		reference_dot += (DOT_TYPE)x[i]*(DOT_TYPE)y[i];
+	} 
+	
+	unsigned block;
+	for (block = 0; block < nblocks; block++)
+	{
+		starpu_vector_data_register(&x_handles[block], 0,
+			(uintptr_t)&x[entries_per_bock*block], entries_per_bock, sizeof(float));
+		starpu_vector_data_register(&y_handles[block], 0,
+			(uintptr_t)&y[entries_per_bock*block], entries_per_bock, sizeof(float));
+	}
+
+	starpu_variable_data_register(&dot_handle, 0, (uintptr_t)&dot, sizeof(DOT_TYPE));
+
+	/*
+	 *	Compute dot product with StarPU
+	 */
+	starpu_data_set_reduction_methods(dot_handle, &redux_codelet, &init_codelet);
+
+	starpu_data_start_reduction_mode(dot_handle);
+
+	for (block = 0; block < nblocks; block++)
+	{
+		struct starpu_task *task = starpu_task_create();
+
+		task->cl = &dot_codelet;
+
+		task->buffers[0].handle = x_handles[block];
+		task->buffers[0].mode = STARPU_R;
+		task->buffers[1].handle = y_handles[block];
+		task->buffers[1].mode = STARPU_R;
+		task->buffers[2].handle = dot_handle;
+		task->buffers[2].mode = STARPU_REDUX;
+
+		int ret = starpu_task_submit(task);
+		STARPU_ASSERT(!ret);
+	}
+
+	starpu_task_wait_for_all();
+
+	starpu_data_end_reduction_mode(dot_handle);
+
+	starpu_data_unregister(dot_handle);
+
+	fprintf(stderr, "Reference : %e vs. %e (Delta %e)\n", reference_dot, dot, reference_dot - dot);
+
+	starpu_helper_cublas_shutdown();
+
+	starpu_shutdown();
+
+	return 0;
+}