Select the fastest OpenCL device automatically

platforms/opencl/include/OpenCLPlatform.h

@@ -55,13 +55,6 @@ public:
     void setPropertyValue(Context& context, const std::string& property, const std::string& value) const;
     void contextCreated(ContextImpl& context) const;
     void contextDestroyed(ContextImpl& context) const;
-    /**
-     * This is the name of the parameter for selecting which OpenCL platform to use.
-     */
-    static const std::string& OpenCLPlatformIndex() {
-        static const std::string key = "OpenCLPlatformIndex";
-        return key;
-    }
     /**
      * This is the name of the parameter for selecting which OpenCL device to use.
      */
@@ -73,7 +66,7 @@ public:
 
 class OpenCLPlatform::PlatformData {
 public:
-    PlatformData(int numParticles, int platformIndex, int deviceIndex);
+    PlatformData(int numParticles, int deviceIndex);
     OpenCLContext* context;
     bool removeCM;
     int cmMotionFrequency;

platforms/opencl/src/OpenCLContext.cpp

@@ -36,16 +36,32 @@
 using namespace OpenMM;
 using namespace std;
 
-OpenCLContext::OpenCLContext(int numParticles, int platformIndex, int deviceIndex) {
-    // TODO Select the platform and device correctly
-    context = cl::Context(CL_DEVICE_TYPE_GPU);
-    device = context.getInfo<CL_CONTEXT_DEVICES>()[0];
+OpenCLContext::OpenCLContext(int numParticles, int deviceIndex) {
+    context = cl::Context(CL_DEVICE_TYPE_ALL);
+    vector<cl::Device> devices = context.getInfo<CL_CONTEXT_DEVICES>();
+    const int minThreadBlockSize = 32;
+    if (deviceIndex < 0 || deviceIndex >= devices.size()) {
+        // Try to figure out which device is the fastest.
+
+        int bestSpeed = 0;
+        for (int i = 0; i < devices.size(); i++) {
+            int maxSize = devices[i].getInfo<CL_DEVICE_MAX_WORK_ITEM_SIZES>()[0];
+            int speed = devices[i].getInfo<CL_DEVICE_MAX_COMPUTE_UNITS>()*devices[i].getInfo<CL_DEVICE_MAX_CLOCK_FREQUENCY>();
+            if (maxSize >= minThreadBlockSize && speed > bestSpeed)
+                deviceIndex = i;
+        }
+    }
+    if (deviceIndex == -1)
+        throw OpenMMException("No compatible OpenCL device is available");
+    device = devices[deviceIndex];
+    if (device.getInfo<CL_DEVICE_MAX_WORK_ITEM_SIZES>()[0] < minThreadBlockSize)
+        throw OpenMMException("The specified OpenCL device is not compatible with OpenMM");
     queue = cl::CommandQueue(context, device);
     numAtoms = numParticles;
     paddedNumAtoms = TileSize*((numParticles+TileSize-1)/TileSize);
     numAtomBlocks = (paddedNumAtoms+(TileSize-1))/TileSize;
     numTiles = numAtomBlocks*(numAtomBlocks+1)/2;
-    numThreadBlocks = 8*device.getInfo<CL_DEVICE_MAX_COMPUTE_UNITS>();
+    numThreadBlocks = device.getInfo<CL_DEVICE_MAX_WORK_ITEM_SIZES>()[0]/ThreadBlockSize;
 
     // Create utility kernels that are used in multiple places.
 

platforms/opencl/src/OpenCLContext.h

@@ -64,7 +64,7 @@ class OpenCLContext {
 public:
     static const int ThreadBlockSize = 64;
     static const int TileSize = 32;
-    OpenCLContext(int numParticles, int platformIndex, int deviceIndex);
+    OpenCLContext(int numParticles, int deviceIndex);
     ~OpenCLContext();
     /**
      * This is called to initialize internal data structures after all Forces in the system

platforms/opencl/src/OpenCLPlatform.cpp

@@ -62,10 +62,8 @@ OpenCLPlatform::OpenCLPlatform() {
 //    registerKernelFactory(ApplyAndersenThermostatKernel::Name(), factory);
     registerKernelFactory(CalcKineticEnergyKernel::Name(), factory);
 //    registerKernelFactory(RemoveCMMotionKernel::Name(), factory);
-    platformProperties.push_back(OpenCLPlatformIndex());
     platformProperties.push_back(OpenCLDeviceIndex());
-    setPropertyDefaultValue(OpenCLPlatformIndex(), "0");
-    setPropertyDefaultValue(OpenCLDeviceIndex(), "0");
+    setPropertyDefaultValue(OpenCLDeviceIndex(), "");
 }
 
 bool OpenCLPlatform::supportsDoublePrecision() const {
@@ -85,16 +83,12 @@ void OpenCLPlatform::setPropertyValue(Context& context, const string& property,
 }
 
 void OpenCLPlatform::contextCreated(ContextImpl& context) const {
-    unsigned int platformIndex = 0;
-    const string& platformPropValue = getPropertyDefaultValue(OpenCLPlatformIndex());
-    if (platformPropValue.length() > 0)
-        stringstream(platformPropValue) >> platformIndex;
-    unsigned int deviceIndex = 0;
+    unsigned int deviceIndex = -1;
     const string& devicePropValue = getPropertyDefaultValue(OpenCLDeviceIndex());
     if (devicePropValue.length() > 0)
         stringstream(devicePropValue) >> deviceIndex;
     int numParticles = context.getSystem().getNumParticles();
-    context.setPlatformData(new PlatformData(numParticles, platformIndex, deviceIndex));
+    context.setPlatformData(new PlatformData(numParticles, deviceIndex));
 }
 
 void OpenCLPlatform::contextDestroyed(ContextImpl& context) const {
@@ -103,12 +97,9 @@ void OpenCLPlatform::contextDestroyed(ContextImpl& context) const {
     delete data;
 }
 
-OpenCLPlatform::PlatformData::PlatformData(int numParticles, int platformIndex, int deviceIndex) : removeCM(false), stepCount(0), computeForceCount(0), time(0.0)  {
-    context = new OpenCLContext(numParticles, platformIndex, deviceIndex);
-    stringstream platform;
-//    device << gpu->platform;
+OpenCLPlatform::PlatformData::PlatformData(int numParticles, int deviceIndex) : removeCM(false), stepCount(0), computeForceCount(0), time(0.0)  {
+    context = new OpenCLContext(numParticles, deviceIndex);
     stringstream device;
 //    device << gpu->device;
-    propertyValues[OpenCLPlatform::OpenCLPlatformIndex()] = platform.str();
     propertyValues[OpenCLPlatform::OpenCLDeviceIndex()] = device.str();
 }