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17. SOCL OpenCL Extensions

SOCL is an OpenCL implementation based on StarPU. It gives unified access to every available OpenCL device: applications can now share entities such as Events, Contexts or Command Queues between several OpenCL implementations.

In addition, command queues that are created without specifying a device provide automatic scheduling of the submitted commands on OpenCL devices contained in the context to which the command queue is attached.

Setting the `CL_QUEUE_OUT_OF_ORDER_EXEC_MODE_ENABLE` flag on a command queue also allows StarPU to reorder kernels queued on the queue, otherwise they would be serialized, and several command queues would be necessary to see kernels dispatched to the various OpenCL devices.

Note: this is still an area under development and subject to change.

When compiling StarPU, SOCL will be enabled if a valid OpenCL implementation is found on your system. To be able to run the SOCL test suite, the environment variable SOCL_OCL_LIB_OPENCL needs to be defined to the location of the file `libOpenCL.so` of the OCL ICD implementation. You should for example add the following line in your file `.bashrc`

    export SOCL_OCL_LIB_OPENCL=/usr/lib/x86_64-linux-gnu/libOpenCL.so

You can then run the test suite in the directory `socl/examples`.

    $ make check
    ...
    PASS: basic/basic
    PASS: testmap/testmap
    PASS: clinfo/clinfo
    PASS: matmul/matmul
    PASS: mansched/mansched
    ==================
    All 5 tests passed
    ==================

The environment variable OCL_ICD_VENDORS has to point to the directory where the socl.icd ICD file is installed. When compiling StarPU, the files are in the directory `socl/vendors`. With an installed version of StarPU, the files are installed in the directory `$prefix/share/starpu/opencl/vendors`.

To run the tests by hand, you have to call, for example,

    $ LD_PRELOAD=$SOCL_OCL_LIB_OPENCL OCL_ICD_VENDORS=socl/vendors/ socl/examples/clinfo/clinfo
    Number of platforms:    2
      Platform Profile:     FULL_PROFILE
      Platform Version:     OpenCL 1.1 CUDA 4.2.1
      Platform Name:        NVIDIA CUDA
      Platform Vendor:      NVIDIA Corporation
      Platform Extensions:  cl_khr_byte_addressable_store cl_khr_icd cl_khr_gl_sharing cl_nv_compiler_options cl_nv_device_attribute_query cl_nv_pragma_unroll

      Platform Profile:     FULL_PROFILE
      Platform Version:     OpenCL 1.0 SOCL Edition (0.1.0)
      Platform Name:        SOCL Platform
      Platform Vendor:      Inria
      Platform Extensions:  cl_khr_icd
    ....
    $

To enable the use of CPU cores via OpenCL, one can set the STARPU_OPENCL_ON_CPUS environment variable to 1 and STARPU_NCPUS to 0 (to avoid using CPUs both via the OpenCL driver and the normal CPU driver).