COMPUTE-8024 Fixed the maximum OpenCL workgroup size

The maximum workgroup size depends on the kernel and the device, rather
than being a property of the device. The present patch fixes the case
when a kernel is queued with no workgroup size and the default workgroup
size is used instead.

A previous patch introduced a maximum workgroup size that depended on
the device but ignored the kernel. In OpenCL the maximum workgroup size
we query from the device is an upper bound of the actual maximum that
we can query for a given kernel running on the same device. For some
kernels the values will match, but for others we will get a lower value
when querying for an specific kernel (i.e. if the kernel uses a high
number of registers).

Change-Id: I3bed6bde80ddc4f0ddb8f82c80903774aa1999b6
Reviewed-on: http://mpd-gerrit.cambridge.arm.com/89471
Tested-by: Kaizen <jeremy.johnson+kaizengerrit@arm.com>
Reviewed-by: Anthony Barbier <anthony.barbier@arm.com>

3 files changed, 24 insertions, 24 deletions

diff --git a/arm_compute/core/CL/CLKernelLibrary.h b/arm_compute/core/CL/CLKernelLibrary.h
index 4d4565d6fd..fc131cdcfe 100644
--- a/arm_compute/core/CL/CLKernelLibrary.h
+++ b/arm_compute/core/CL/CLKernelLibrary.h
@@ -162,11 +162,9 @@ public:
      */
     void init(std::string kernel_path = ".", cl::Context context = cl::Context::getDefault(), cl::Device device = cl::Device::getDefault())
     {
-        _kernel_path        = std::move(kernel_path);
-        _context            = std::move(context);
-        _device             = std::move(device);
-        _max_workgroup_size = 0;
-        max_local_workgroup_size();
+        _kernel_path = std::move(kernel_path);
+        _context     = std::move(context);
+        _device      = std::move(device);
     }
     /** Sets the path that the kernels reside in.
      *
@@ -208,20 +206,15 @@ public:
         {
             _device = cl_devices[0];
         }
-
-        _max_workgroup_size = 0;
-        max_local_workgroup_size();
-    };
+    }
     /** Sets the CL device for which the programs are created.
      *
      * @param[in] device A CL device.
      */
     void set_device(cl::Device device)
     {
-        _device             = std::move(device);
-        _max_workgroup_size = 0;
-        max_local_workgroup_size();
-    };
+        _device = std::move(device);
+    }
     /** Creates a kernel from the kernel library.
      *
      * @param[in] kernel_name       Kernel name.
@@ -238,15 +231,14 @@ public:
      *
      */
     void load_binary();
-    /** Find the maximum number of local work items in a workgroup can be supported by the device
+    /** Find the maximum number of local work items in a workgroup can be supported for the kernel.
      *
      */
-    size_t max_local_workgroup_size();
-
-    /** Return the default NDRange that is suitable for the device.
+    size_t max_local_workgroup_size(const cl::Kernel &kernel) const;
+    /** Return the default NDRange for the device.
      *
      */
-    cl::NDRange default_ndrange();
+    cl::NDRange default_ndrange() const;
 
 private:
     /** Load program and its dependencies.
@@ -270,7 +262,6 @@ private:
     static const std::map<std::string, std::string> _kernel_program_map; /**< Map that associates kernel names with programs. */
     static const std::map<std::string, std::string> _program_source_map; /**< Contains sources for all programs.
                                                                               Used for compile-time kernel inclusion. >*/
-    size_t _max_workgroup_size;                                          /** Maximum local workgroup size supported on the device */
 };
 }
 #endif /* __ARM_COMPUTE_CLKERNELLIBRARY_H__ */
diff --git a/arm_compute/core/CL/ICLKernel.h b/arm_compute/core/CL/ICLKernel.h
index d118d13f3f..9119940bc5 100644
--- a/arm_compute/core/CL/ICLKernel.h
+++ b/arm_compute/core/CL/ICLKernel.h
@@ -175,6 +175,12 @@ public:
      */
     GPUTarget get_target() const;
 
+    /** Get the maximum workgroup size for the device the CLKernelLibrary uses.
+     *
+     * @return The maximum workgroup size value.
+     */
+    size_t get_max_workgroup_size();
+
 private:
     /** Add the passed array's parameters to the object's kernel's arguments starting from the index idx.
      *
@@ -208,10 +214,11 @@ private:
     unsigned int           num_arguments_per_tensor() const;
 
 protected:
-    cl::Kernel  _kernel;    /**< OpenCL kernel to run */
-    cl::NDRange _lws_hint;  /**< Local workgroup size hint for the OpenCL kernel */
-    GPUTarget   _target;    /**< The targeted GPU */
-    std::string _config_id; /**< Configuration ID */
+    cl::Kernel  _kernel;             /**< OpenCL kernel to run */
+    cl::NDRange _lws_hint;           /**< Local workgroup size hint for the OpenCL kernel */
+    GPUTarget   _target;             /**< The targeted GPU */
+    std::string _config_id;          /**< Configuration ID */
+    size_t      _max_workgroup_size; /**< The maximum workgroup size for this kernel */
 };
 
 /** Add the kernel to the command queue with the given window.
@@ -223,7 +230,7 @@ protected:
  * @param[in,out] queue    OpenCL command queue.
  * @param[in]     kernel   Kernel to enqueue
  * @param[in]     window   Window the kernel has to process.
- * @param[in]     lws_hint Local workgroup size requested, by default (128,1)
+ * @param[in]     lws_hint Local workgroup size requested, by default (128,1).
  *
  * @note If any dimension of the lws is greater than the global workgroup size then no lws will be passed.
  */
diff --git a/arm_compute/core/CL/OpenCL.h b/arm_compute/core/CL/OpenCL.h
index 151cc9b53d..6780e23c2d 100644
--- a/arm_compute/core/CL/OpenCL.h
+++ b/arm_compute/core/CL/OpenCL.h
@@ -84,6 +84,7 @@ public:
     using clGetDeviceIDs_func            = cl_int (*)(cl_platform_id, cl_device_type, cl_uint, cl_device_id *, cl_uint *);
     using clRetainEvent_func             = cl_int (*)(cl_event);
     using clGetPlatformIDs_func          = cl_int (*)(cl_uint, cl_platform_id *, cl_uint *);
+    using clGetKernelWorkGroupInfo_func  = cl_int (*)(cl_kernel, cl_device_id, cl_kernel_work_group_info, size_t, void *, size_t *);
 
     clBuildProgram_func            clBuildProgram            = nullptr;
     clEnqueueNDRangeKernel_func    clEnqueueNDRangeKernel    = nullptr;
@@ -115,6 +116,7 @@ public:
     clGetDeviceIDs_func            clGetDeviceIDs            = nullptr;
     clRetainEvent_func             clRetainEvent             = nullptr;
     clGetPlatformIDs_func          clGetPlatformIDs          = nullptr;
+    clGetKernelWorkGroupInfo_func  clGetKernelWorkGroupInfo  = nullptr;
 
 private:
     std::pair<bool, bool> _loaded{ false, false };