initial version

include/CL/opencl.hpp

@@ -1799,6 +1799,12 @@ CL_HPP_DECLARE_PARAM_TRAITS_(cl_mutable_command_info_khr, CL_MUTABLE_DISPATCH_LO
 CL_HPP_DECLARE_PARAM_TRAITS_(cl_device_info, CL_DEVICE_KERNEL_CLOCK_CAPABILITIES_KHR, cl_device_kernel_clock_capabilities_khr)
 #endif /* cl_khr_kernel_clock */
 
+#if defined(cl_ext_float_atomics)
+CL_HPP_DECLARE_PARAM_TRAITS_(cl_device_info, CL_DEVICE_SINGLE_FP_ATOMIC_CAPABILITIES_EXT, cl_device_fp_atomic_capabilities_ext)
+CL_HPP_DECLARE_PARAM_TRAITS_(cl_device_info, CL_DEVICE_DOUBLE_FP_ATOMIC_CAPABILITIES_EXT, cl_device_fp_atomic_capabilities_ext)
+CL_HPP_DECLARE_PARAM_TRAITS_(cl_device_info, CL_DEVICE_HALF_FP_ATOMIC_CAPABILITIES_EXT, cl_device_fp_atomic_capabilities_ext)
+#endif /* cl_ext_float_atomics */
+
 #if defined(cl_intel_command_queue_families)
 CL_HPP_PARAM_NAME_CL_INTEL_COMMAND_QUEUE_FAMILIES_(CL_HPP_DECLARE_PARAM_TRAITS_)
 #endif // cl_intel_command_queue_families

samples/16_floatatomics/CMakeLists.txt

@@ -0,0 +1,10 @@
+# Copyright (c) 2019-2024 Ben Ashbaugh
+#
+# SPDX-License-Identifier: MIT
+
+add_opencl_sample(
+    TEST
+    NUMBER 16
+    TARGET floatatomics
+    VERSION 120
+    SOURCES main.cpp)

samples/16_floatatomics/README.md

@@ -0,0 +1,21 @@
+# Floating-point Atomic Adds
+
+## Sample Purpose
+
+TODO
+
+Inspired by: https://pipinspace.github.io/blog/atomic-float-addition-in-opencl.html
+
+## Key APIs and Concepts
+
+TODO
+
+## Command Line Options
+
+| Option | Default Value | Description |
+|:--|:-:|:--|
+| `-d <index>` | 0 | Specify the index of the OpenCL device in the platform to execute on the sample on.
+| `-p <index>` | 0 | Specify the index of the OpenCL platform to execute the sample on.
+| `-i <number>` | 16 | Specify the number of iterations to execute.
+| `--gwx <number>` | 1024 | Specify the global work size to execute, which is also the number of floating-point atomics to perform.
+| `-e` | N/A | Unconditionally use the emulated floating-point atomic add.

samples/16_floatatomics/main.cpp

@@ -0,0 +1,205 @@
+/*
+// Copyright (c) 2019-2024 Ben Ashbaugh
+//
+// SPDX-License-Identifier: MIT
+*/
+
+#include <popl/popl.hpp>
+
+#include <CL/opencl.hpp>
+
+#include <chrono>
+#include <cinttypes>
+
+#include "util.hpp"
+
+static const char kernelString[] = R"CLC(
+inline float atomic_add_f(volatile global float* addr, float val)
+{
+    #if defined(__opencl_c_ext_fp32_global_atomic_add) && !defined(EMULATE)
+        //#pragma message("using cl_ext_float_atomics")
+        return atomic_fetch_add_explicit((volatile global atomic_float*)addr, val, memory_order_relaxed);
+    #elif defined(cl_nv_pragma_unroll) && !defined(EMULATE)
+        //#pragma message("using PTX atomics")
+        float ret; asm volatile("atom.global.add.f32 %0,[%1],%2;":"=f"(ret):"l"(addr),"f"(val):"memory");
+        return ret;
+    #else // fallback, see: https://forums.developer.nvidia.com/t/atomicadd-float-float-atomicmul-float-float/14639/7
+        //#pragma message("using emulated float atomics")
+        float ret = atomic_xchg(addr, 0.0f);
+        float old = ret + val;
+        while((old = atomic_xchg(addr, old)) != 0.0f) {
+            old = atomic_xchg(addr, 0.0f) + old;
+        }
+        return ret;
+    #endif
+}
+
+kernel void FloatAtomicTest(global float* dst)
+{
+    atomic_add_f(dst, 1.0f);
+}
+)CLC";
+
+static void PrintFloatAtomicCapabilities(
+    cl_device_fp_atomic_capabilities_ext caps )
+{
+    if (caps & CL_DEVICE_GLOBAL_FP_ATOMIC_LOAD_STORE_EXT ) printf("\t\tCL_DEVICE_GLOBAL_FP_ATOMIC_LOAD_STORE_EXT\n");
+    if (caps & CL_DEVICE_GLOBAL_FP_ATOMIC_ADD_EXT        ) printf("\t\tCL_DEVICE_GLOBAL_FP_ATOMIC_ADD_EXT\n");
+    if (caps & CL_DEVICE_GLOBAL_FP_ATOMIC_MIN_MAX_EXT    ) printf("\t\tCL_DEVICE_GLOBAL_FP_ATOMIC_MIN_MAX_EXT\n");
+    if (caps & CL_DEVICE_LOCAL_FP_ATOMIC_LOAD_STORE_EXT  ) printf("\t\tCL_DEVICE_LOCAL_FP_ATOMIC_LOAD_STORE_EXT\n");
+    if (caps & CL_DEVICE_LOCAL_FP_ATOMIC_ADD_EXT         ) printf("\t\tCL_DEVICE_LOCAL_FP_ATOMIC_ADD_EXT\n");
+    if (caps & CL_DEVICE_LOCAL_FP_ATOMIC_MIN_MAX_EXT     ) printf("\t\tCL_DEVICE_LOCAL_FP_ATOMIC_MIN_MAX_EXT\n");
+
+    cl_device_command_buffer_capabilities_khr extra = caps & ~(
+        CL_DEVICE_GLOBAL_FP_ATOMIC_LOAD_STORE_EXT |
+        CL_DEVICE_GLOBAL_FP_ATOMIC_ADD_EXT |
+        CL_DEVICE_GLOBAL_FP_ATOMIC_MIN_MAX_EXT |
+        CL_DEVICE_LOCAL_FP_ATOMIC_LOAD_STORE_EXT |
+        CL_DEVICE_LOCAL_FP_ATOMIC_ADD_EXT |
+        CL_DEVICE_LOCAL_FP_ATOMIC_MIN_MAX_EXT );
+    if (extra) {
+        printf("\t\t(Unknown capability: %016" PRIx64 ")\n", extra);
+    }
+}
+
+int main(
+    int argc,
+    char** argv )
+{
+    int platformIndex = 0;
+    int deviceIndex = 0;
+
+    size_t iterations = 16;
+    size_t gwx = 1024 * 1024;
+
+    bool emulate = false;
+
+    {
+        popl::OptionParser op("Supported Options");
+        op.add<popl::Value<int>>("p", "platform", "Platform Index", platformIndex, &platformIndex);
+        op.add<popl::Value<int>>("d", "device", "Device Index", deviceIndex, &deviceIndex);
+        op.add<popl::Value<size_t>>("i", "iterations", "Iterations", iterations, &iterations);
+        op.add<popl::Value<size_t>>("", "gwx", "Global Work Size X AKA Number of Atomics", gwx, &gwx);
+        op.add<popl::Switch>("e", "emulate", "Unconditionally Emulate Float Atomics", &emulate);
+
+        bool printUsage = false;
+        try {
+            op.parse(argc, argv);
+        } catch (std::exception& e) {
+            fprintf(stderr, "Error: %s\n\n", e.what());
+            printUsage = true;
+        }
+
+        if (printUsage || !op.unknown_options().empty() || !op.non_option_args().empty()) {
+            fprintf(stderr,
+                "Usage: floatatomics [options]\n"
+                "%s", op.help().c_str());
+            return -1;
+        }
+    }
+
+    std::vector<cl::Platform> platforms;
+    cl::Platform::get(&platforms);
+
+    printf("Running on platform: %s\n",
+        platforms[platformIndex].getInfo<CL_PLATFORM_NAME>().c_str() );
+
+    std::vector<cl::Device> devices;
+    platforms[platformIndex].getDevices(CL_DEVICE_TYPE_ALL, &devices);
+
+    printf("Running on device: %s\n",
+        devices[deviceIndex].getInfo<CL_DEVICE_NAME>().c_str() );
+
+    if (checkDeviceForExtension(devices[deviceIndex], CL_EXT_FLOAT_ATOMICS_EXTENSION_NAME)) {
+        printf("Device supports " CL_EXT_FLOAT_ATOMICS_EXTENSION_NAME ".\n");
+
+        cl_device_fp_atomic_capabilities_ext spcaps =
+            devices[deviceIndex].getInfo<CL_DEVICE_SINGLE_FP_ATOMIC_CAPABILITIES_EXT>();
+        printf("CL_DEVICE_SINGLE_FP_ATOMIC_CAPABILITIES_EXT:\n");
+        PrintFloatAtomicCapabilities(spcaps);
+
+        cl_device_fp_atomic_capabilities_ext dpcaps =
+            devices[deviceIndex].getInfo<CL_DEVICE_DOUBLE_FP_ATOMIC_CAPABILITIES_EXT>();
+        printf("CL_DEVICE_DOUBLE_FP_ATOMIC_CAPABILITIES_EXT:\n");
+        PrintFloatAtomicCapabilities(dpcaps);
+
+        cl_device_fp_atomic_capabilities_ext hpcaps =
+            devices[deviceIndex].getInfo<CL_DEVICE_HALF_FP_ATOMIC_CAPABILITIES_EXT>();
+        printf("CL_DEVICE_HALF_FP_ATOMIC_CAPABILITIES_EXT:\n");
+        PrintFloatAtomicCapabilities(hpcaps);
+
+        if (spcaps & CL_DEVICE_GLOBAL_FP_ATOMIC_ADD_EXT == 0) {
+            printf("Device does not support fp32 atomic add.\n");
+        }
+    } else {
+        printf("Device does not support " CL_EXT_FLOAT_ATOMICS_EXTENSION_NAME ".\n");
+    }
+
+    cl::Context context{devices[deviceIndex]};
+    cl::CommandQueue commandQueue{context, devices[deviceIndex]};
+
+    cl::Program program{ context, kernelString };
+    std::string buildOptions = "-cl-std=CL3.0";
+
+    if (emulate) {
+        printf("Forcing emulation.\n");
+        buildOptions += " -DEMULATE";
+    }
+
+    program.build(buildOptions);
+    cl::Kernel kernel = cl::Kernel{ program, "FloatAtomicTest" };
+
+    cl::Buffer deviceMemDst = cl::Buffer{
+        context,
+        CL_MEM_READ_WRITE,
+        sizeof(cl_float) };
+
+    // execution
+    {
+        kernel.setArg(0, deviceMemDst);
+
+        // Ensure the queue is empty and no processing is happening
+        // on the device before starting the timer.
+        commandQueue.finish();
+
+        auto start = std::chrono::system_clock::now();
+        for( size_t i = 0; i < iterations; i++ )
+        {
+            cl_float zero = 0.0f;
+            commandQueue.enqueueFillBuffer(
+                deviceMemDst,
+                zero,
+                0,
+                sizeof(zero));
+            commandQueue.enqueueNDRangeKernel(
+                kernel,
+                cl::NullRange,
+                cl::NDRange{gwx});
+        }
+
+        // Ensure all processing is complete before stopping the timer.
+        commandQueue.finish();
+
+        auto end = std::chrono::system_clock::now();
+        std::chrono::duration<float> elapsed_seconds = end - start;
+        printf("Finished in %f seconds\n", elapsed_seconds.count());
+    }
+
+    // validation
+    {
+        cl_float result = 0.0f;
+        commandQueue.enqueueReadBuffer(
+            deviceMemDst,
+            CL_TRUE,
+            0,
+            sizeof(result),
+            &result);
+        if (result != (float)gwx) {
+            printf("Error: expected %f, got %f!\n", (float)gwx, result);
+        } else {
+            printf("Success.\n");
+        }
+    }
+
+    return 0;
+}

samples/CMakeLists.txt

@@ -75,6 +75,7 @@ add_subdirectory( 05_spirvkernelfromfile )
 add_subdirectory( 06_ndrangekernelfromfile )
 
 add_subdirectory( 10_queueexperiments )
+add_subdirectory( 16_floatatomics )
 
 set(BUILD_EXTENSION_SAMPLES TRUE)
 if(NOT TARGET OpenCLExt)