Wrong calculation results on Intel(R) HD Graphics 4600

[Joseph_A_2]

Hi,

I've found what seems to be a bug in the OpenCL driver for Intel HD 4600 graphics core. The code I am attaching produces correct results on Intel CPU or NVidia GPU OpenCL targets but at the same time produces wrong results on HD 4600.

The code is self-diagnosing. It tells you if it produces correct or incorrect results. Here is the output I am getting on HD 4600:

Device: Intel(R) HD Graphics 4600
Expected value at center: 1.06103
Computed value at center: 0.000547921
MSE: 0.0778968 [FAIL]
 

After a small modification to select a CPU device it produces the following:

Device: Intel(R) Core(TM) i7-4700HQ CPU @ 2.40GHz
Expected value at center: 1.06103
Computed value at center: 1.06335
MSE: 7.60111e-005 [PASS]

I am compiling the code with Visual Studio 2013 using Khronos OpenCL headers (.h files from OpenCL 1.1 and cl.hpp from OpenCL 1.2) and linking against opencl.lib from NVidia's SDK. It shouldn't matter though.

I am running Windows 8.1 with the latest driver 10.18.14.4222.

 

[Robert_I_Intel]

Hi Joseph,

Sorry for getting back to you so late: I was on vacation.

Thank you very much for submitting the reproducer: I can see the problem on HD 5200 as well (HSW), but not on earlier IVB with HD 4000 with 10.18.10.4226 driver. I will submit a bug report and update you on the progress.

[Robert_I_Intel]

Hi Joseph,

Please use -cl-fast-relaxed-math flag when building your program for now: your program should work.

cl::Program program(context, kernel_source);

program.build("-cl-fast-relaxed-math");

This definitely looks like a bug: we will figure out whether this is a driver issue or the hardware issue.

[Zeshan_A_]

Hi All,

i have purchased the new intel i7 core processor   with built-in HD graphics cards.

i want to use the Intel OpenCL SDK  on ubuntu 14.04 . 

i would like to ask , Intel HD graphics card support the Ubuntu OS  14.04 LTE .i mean its support the GPU computing using Intel OpenCL SDK .

Best regards,

Zeshan

[Robert_I_Intel]

Hi Zeshan,

Ubuntu is not a supported platform, especially Ubuntu 14.04. Please see https://software.intel.com/en-us/forums/topic/390630 - I believe you posted to that forum as well. You may try upgrading to Ubuntu 14.10 for better results, but still, supported platforms are CentOS and SLES.

I didn't have much luck making OpenCL work on Ubuntu on Intel GPU. CPU version works though, but then you are not utilizing all available resources.