add a test for timer drift

Author: bashbaug

samples/99_timerdrift/CMakeLists.txt

@@ -0,0 +1,10 @@
+# Copyright (c) 2025 Ben Ashbaugh
+#
+# SPDX-License-Identifier: MIT
+
+add_opencl_sample(
+    TEST
+    NUMBER 99
+    TARGET timerdrift
+    VERSION 300
+    SOURCES main.cpp)

samples/99_timerdrift/main.cpp

@@ -0,0 +1,106 @@
+/*
+// Copyright (c) 2025 Ben Ashbaugh
+//
+// SPDX-License-Identifier: MIT
+*/
+
+#include <popl/popl.hpp>
+
+#include <CL/opencl.hpp>
+
+#include <iostream>
+#include <chrono>
+#include <ctime>
+#include <thread>
+
+#include <cinttypes>
+
+void getGlobalTimeStamps(cl::Device& device,
+    uint64_t *DeviceTimestamp,
+    uint64_t *HostTimestamp)
+{
+    auto times = device.getDeviceAndHostTimer();
+
+    if (DeviceTimestamp) {
+        *DeviceTimestamp = times.first;
+    }
+    if (HostTimestamp) {
+        *HostTimestamp = times.second;
+    }
+}
+
+int main(int argc, char** argv)
+{
+    int platformIndex = 0;
+    int deviceIndex = 0;
+
+    {
+        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);
+
+        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: timerdrift [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() );
+
+    uint64_t BaseHostTime = 0, CurrentHostTime = 0, BaseDeviceTime = 0, CurrentDeviceTime = 0;
+
+    for (int i = 0; i < 32; i++) {
+        if (i == 0) {
+            getGlobalTimeStamps(devices[deviceIndex], &BaseDeviceTime, &BaseHostTime);
+            CurrentDeviceTime = BaseDeviceTime;
+            CurrentHostTime = BaseHostTime;
+        } else {
+            getGlobalTimeStamps(devices[deviceIndex], &CurrentDeviceTime, &CurrentHostTime);
+        }
+        auto DeviceTimePast = CurrentDeviceTime - BaseDeviceTime;
+        auto HostTimePast = CurrentHostTime - BaseHostTime;
+#if 0
+        std::cout << "Iteration: " << i << std::endl;
+        std::cout << "Device time past since base time: " << DeviceTimePast
+                    << std::endl;
+        std::cout << "Host time past since base time: " << HostTimePast
+                    << std::endl;
+        std::cout << "Abs diff: "
+                    << std::abs((int64_t)HostTimePast - (int64_t)DeviceTimePast)
+                    << std::endl
+                    << std::endl;
+#else
+        printf("Iteration: %2d, Delta: %" PRId64 "\n",
+            i, (int64_t)HostTimePast - (int64_t)DeviceTimePast);
+#endif
+
+        // Emulate the first iteration taking longer
+        if (i == 0) {
+            std::this_thread::sleep_for(std::chrono::milliseconds(500));
+        } else {
+            std::this_thread::sleep_for(std::chrono::milliseconds(50));
+        }
+    }
+
+    return 0;
+}

samples/CMakeLists.txt

@@ -78,6 +78,8 @@ add_subdirectory( 06_ndrangekernelfromfile )
 add_subdirectory( 10_queueexperiments )
 add_subdirectory( 16_floatatomics )
 
+add_subdirectory( 99_timerdrift )
+
 set(BUILD_EXTENSION_SAMPLES TRUE)
 if(NOT TARGET OpenCLExt)
     message(STATUS "Skipping Extension Samples - OpenCL Extension Loader is not found.")