adding simple histogram excample

Author: leios

examples/histogram.jl

@@ -0,0 +1,116 @@
+using Test
+using CUDA
+using CUDAKernels
+using KernelAbstractions
+
+# Function to use as a baseline for CPU metrics
+function create_histogram(input)
+    histogram_output = zeros(Int, maximum(input))
+    for i = 1:length(input)
+        histogram_output[input[i]] += 1
+    end
+    return histogram_output
+end
+
+# This a 1D histogram kernel where the histogramming happens on shmem
+@kernel function histogram_kernel!(histogram_output, input)
+    tid = @index(Global, Linear)
+    lid = @index(Local, Linear)
+
+    @uniform warpsize = Int(32)
+
+    @uniform gs = @groupsize()[1]
+    @uniform N = length(histogram_output)
+
+    shared_histogram = @localmem Int (gs)
+
+    # This will go through all input elements and assign them to a location in
+    # shmem. Note that if there is not enough shem, we create different shmem
+    # blocks to write to. For example, if shmem is of size 256, but it's
+    # possible to get a value of 312, then we will have 2 separate shmem blocks,
+    # one from 1->256, and another from 256->512
+    @uniform max_element = 1
+    for min_element = 1:gs:N
+
+        # Setting shared_histogram to 0
+        @inbounds shared_histogram[lid] = 0
+        @synchronize()
+
+        max_element = min_element + gs
+        if max_element > N
+            max_element = N+1
+        end
+
+        # Defining bin on shared memory and writing to it if possible
+        bin = input[tid]
+        if bin >= min_element && bin < max_element
+            bin -= min_element-1
+            atomic_add!(pointer(shared_histogram, bin), Int(1))
+        end
+
+        @synchronize()
+
+        if ((lid+min_element-1) <= N)
+            atomic_add!(pointer(histogram_output, lid+min_element-1),
+                        shared_histogram[lid])
+        end
+
+    end
+
+end
+
+function histogram!(histogram_output, input;
+                    numcores = 4, numthreads = 256)
+
+    if isa(input, Array)
+        kernel! = histogram_kernel!(CPU(), numcores)
+    else
+        kernel! = histogram_kernel!(CUDADevice(), numthreads)
+    end
+
+    kernel!(histogram_output, input, ndrange=size(input))
+end
+
+@testset "histogram tests" begin
+
+    rand_input = [rand(1:128) for i = 1:1000]
+    linear_input = [i for i = 1:1024]
+    all_2 = [2 for i = 1:512]
+
+    histogram_rand_baseline = create_histogram(rand_input)
+    histogram_linear_baseline = create_histogram(linear_input)
+    histogram_2_baseline = create_histogram(all_2)
+
+    CPU_rand_histogram = zeros(Int, 128)
+    CPU_linear_histogram = zeros(Int, 1024)
+    CPU_2_histogram = zeros(Int, 2)
+
+    wait(histogram!(CPU_rand_histogram, rand_input))
+    wait(histogram!(CPU_linear_histogram, linear_input))
+    wait(histogram!(CPU_2_histogram, all_2))
+
+    @test isapprox(CPU_rand_histogram, histogram_rand_baseline)
+    @test isapprox(CPU_linear_histogram, histogram_linear_baseline)
+    @test isapprox(CPU_2_histogram, histogram_2_baseline)
+
+    if has_cuda_gpu()
+        CUDA.allowscalar(false)
+
+        GPU_rand_input = CuArray(rand_input)
+        GPU_linear_input = CuArray(linear_input)
+        GPU_2_input = CuArray(all_2)
+
+        GPU_rand_histogram = CuArray(zeros(Int, 128))
+        GPU_linear_histogram = CuArray(zeros(Int, 1024))
+        GPU_2_histogram = CuArray(zeros(Int, 2))
+
+        wait(histogram!(GPU_rand_histogram, GPU_rand_input))
+        wait(histogram!(GPU_linear_histogram, GPU_linear_input))
+        wait(histogram!(GPU_2_histogram, GPU_2_input))
+
+        @test isapprox(Array(GPU_rand_histogram), histogram_rand_baseline)
+        @test isapprox(Array(GPU_linear_histogram), histogram_linear_baseline)
+        @test isapprox(Array(GPU_2_histogram), histogram_2_baseline)
+    end
+
+end