Performance hint: Null local workgroup size detected...

[matteo_m_1]

My application uses a 2D kernel that is called several times on different data. Running the code builder profiler, I got a lot of the following perfromance hints (on Intel HD 4600, Windows 10, Intel SDK for OpenCL Applications 2016 R3 ):

Performance hint: Null local workgroup size detected (kernel name: cellRasterize); following sizes will be used for execution: { 20, 22, 1 }

Performance hint: Null local workgroup size detected (kernel name: cellRasterize); following sizes will be used for execution: { 26, 16, 1 }

Performance hint: Null local workgroup size detected (kernel name: cellRasterize); following sizes will be used for execution: { 12, 12, 1 }

...

What does it mean?  Many Thanks in advance!

    Matteo.

[Ben_A_Intel]

These lines are purely informational and tell you what local work size the driver chose for this kernel since you didn't specify one explicitly.  They're not anything to worry about, but you may find this information useful when optimizing your kernel.

As background, the Code Builder profiler is using the "driver diagnostics" OpenCL extension to get this information:

https://www.khronos.org/registry/cl/extensions/intel/cl_intel_driver_diagnostics.txt

This particular performance hint falls under the category "CL_CONTEXT_DIAGNOSTICS_LEVEL_NEUTRAL_INTEL".

[Michal_M_Intel]

This article may be useful as well:

https://software.intel.com/en-us/articles/application-performance-using-intel-opencl-driver-diagnostics-sample-users-guide