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OpenCL

skn1975
Adept I

AMDGPU OpenCL Weird Results

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Hello AMD OpenCL Gurus. I am facing a problem when building and running an opencl example. Here are details of my setup:

a.) I installed amdgpu-pro-install --opencl=legacy --headless

b.) I get the output from clinfo as

Output from clinfo (which w

Number of platforms:     1
  Platform Profile:     FULL_PROFILE
  Platform Version:     OpenCL 2.1 AMD-APP (2639.3)
  Platform Name:     AMD Accelerated Parallel Processing
  Platform Vendor:     Advanced Micro Devices, Inc.
  Platform Extensions:     cl_khr_icd cl_amd_event_callback cl_amd_offline_devices

  Platform Name:     AMD Accelerated Parallel Processing
Number of devices:     1
  Device Type:     CL_DEVICE_TYPE_GPU
  Vendor ID:     1002h
  Board name:     AMD Radeon (TM) R5 M340
  Device Topology:     PCI[ B#1, D#0, F#0 ]
  Max compute units:     5
  Max work items dimensions:     3
Max work items[0]:     1024
Max work items[1]:     1024
Max work items[2]:     1024
  Max work group size:     256
  Preferred vector width char:     4
  Preferred vector width short:     2
  Preferred vector width int:     1
  Preferred vector width long:     1
  Preferred vector width float:     1
  Preferred vector width double:     1
  Native vector width char:     4
  Native vector width short:     2
  Native vector width int:     1
  Native vector width long:     1
  Native vector width float:     1
  Native vector width double:     1
  Max clock frequency:     750Mhz
  Address bits:     64
  Max memory allocation:     1596905472
  Image support:     Yes
  Max number of images read arguments:     128
  Max number of images write arguments:     8
  Max image 2D width:     16384
  Max image 2D height:     16384
  Max image 3D width:     2048
  Max image 3D height:     2048
  Max image 3D depth:     2048
  Max samplers within kernel:     16
  Max size of kernel argument:     1024
  Alignment (bits) of base address:     2048

  Minimum alignment (bytes) for any datatype:     128

  Single precision floating point capability

Denorms:     No
Quiet NaNs:     Yes
Round to nearest even:     Yes
Round to zero:     Yes
Round to +ve and infinity:     Yes
IEEE754-2008 fused multiply-add:     Yes
  Cache type:     Read/Write
  Cache line size:     64
  Cache size:     16384
  Global memory size:     2146349056
  Constant buffer size:     65536
  Max number of constant args:     8
  Local memory type:     Scratchpad
  Local memory size:     32768
  Max pipe arguments:     0
  Max pipe active reservations:     0
  Max pipe packet size:     0
  Max global variable size:     0

  Max global variable preferred total size:     0

  Max read/write image args:     0
  Max on device events:     0
  Queue on device max size:     0
  Max on device queues:     0
  Queue on device preferred size:     0
  SVM capabilities:    
Coarse grain buffer:     No
Fine grain buffer:     No
Fine grain system:     No
Atomics:     No
  Preferred platform atomic alignment:     0
  Preferred global atomic alignment:     0
  Preferred local atomic alignment:     0

  Kernel Preferred work group size multiple:     64

  Error correction support:     0
  Unified memory for Host and Device:     0
  Profiling timer resolution:     1
  Device endianess:     Little
  Available:     Yes
  Compiler available:     Yes
  Execution capabilities:    
Execute OpenCL kernels:     Yes
Execute native function:     No
  Queue on Host properties:    
Out-of-Order:     No
Profiling :     Yes
  Queue on Device properties:    
Out-of-Order:     No
Profiling :     No
  Platform ID:     0x7fdcfda149f0
  Name:     Hainan
  Vendor:     Advanced Micro Devices, Inc.
  Device OpenCL C version:     OpenCL C 1.2
  Driver version:     2639.3
  Profile:     FULL_PROFILE
  Version:     OpenCL 1.2 AMD-APP (2639.3)
  Extensions:     cl_khr_fp64 cl_amd_fp64 cl_khr_global_int32_base_atomics cl_khr_global_int32_extended_atomics cl_khr_local_int32_base_atomics cl_khr_local_int32_extended_atomics cl_khr_int64_base_atomics cl_khr_int64_extended_atomics cl_khr_3d_image_writes cl_khr_byte_addressable_store cl_khr_gl_sharing cl_amd_device_attribute_query cl_amd_vec3 cl_amd_printf cl_amd_media_ops cl_amd_media_ops2 cl_amd_popcnt cl_khr_image2d_from_buffer cl_khr_spir cl_khr_gl_event

c.) As per the AMD website, this card is supported.

d.) I build the helloworld example from

     https://raw.githubusercontent.com/bgaster/opencl-book-samples/master/src/Chapter_2/HelloWorld/HelloW...

e.) So far so good. However when I try to run the example I get the following bugs:

     1.) "Failed to create commandQueue for device". This was also pointed out by some users and I followed the fix listed here

           Bug #11702: Cannot use opencl on Cape Verde: [opencl_init] could not create command queue for device...

      2.) Now once I enabled those exports the code behaves erratically. If I run the code for the first time, I get the following output (garbage)

-1.70674e+38 -1.70674e+38 2.34731e-38 2.34731e-38 3.63613e+23 3.63613e+23 -1.18942e-23 -3.04413e-21 -1.17842e+08 -2.31435e-32 7.57767e-16 ...... (omitted the rest of the output)

      3.) If I run the code immediately, I get the correct output as:

0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60 63 66 69 72 75 78 81 84 87 90 93 96 99 102 105 108....

      4.) If I pause and then run the code again I get garbage.

So my question is what is happening here? Is there a problem with the OpenCL driver and can we have a fix? Can anyone from AMD comment on this problem?

1 Solution

Accepted Solutions
rdemaria
Adept I

Re: AMDGPU OpenCL Weird Results

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I see the same problem with a Radeon 280X, Tahiti, SI. It looks like that the data transfer from device to host is somehow broken. It appears that enqueuing any kernel (even a do-nothing one) after the real kernel fixes the problem. See this example:

https://github.com/rdemaria/sixtracklib_gsoc18/blob/master/studies/study0/hello_workaround.cpp

I have not tested this solution thoroughly, but it looks it is working. This explains why several opencl codes do actually work with these drivers and devices.

Needless to say, it is very frustrating to be forced to either use a 4 year old linux kernel and drivers or spend ages on questionable workarounds.

I would really appreciate if some driver developer could shed some light on this issue.

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dipak
Staff
Staff

Re: AMDGPU OpenCL Weird Results

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It looks like a "Hainan" series card which is based on 1st generation GCN  (SI family). And as I know, currently ampdgpu-pro does not support OpenCL on SI cards.

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skn1975
Adept I

Re: AMDGPU OpenCL Weird Results

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Radeon™ Software for Linux® 18.20 Release Notes

AMD Radeon™ R5 340 is listed there. Is there some way to replicate this problem at your end?

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dipak
Staff
Staff

Re: AMDGPU OpenCL Weird Results

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Above card (R5 m3xxx) seems a mobile gpu where as R5 340 is a desktop model. Anyway,  R5 340 is also based on GCN 1.0 which is not supported for OpenCL. The release note lists those cards which are supported by the base display driver. Please check the "Base Feature support" section which says:

OpenCL™1.2 (not supported for 1st generation GCN products)

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skn1975
Adept I

Re: AMDGPU OpenCL Weird Results

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OpenCL™1.2 (not supported for 1st generation GCN products) is perfect for me. It should, however support 1.1? Is there something (as in flags, #define) that I need to setup so that I can at least get 1.1 running?

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dipak
Staff
Staff

Re: AMDGPU OpenCL Weird Results

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No, it does not support any OpenCL version.

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rdemaria
Adept I

Re: AMDGPU OpenCL Weird Results

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I see the same problem with a Radeon 280X, Tahiti, SI. It looks like that the data transfer from device to host is somehow broken. It appears that enqueuing any kernel (even a do-nothing one) after the real kernel fixes the problem. See this example:

https://github.com/rdemaria/sixtracklib_gsoc18/blob/master/studies/study0/hello_workaround.cpp

I have not tested this solution thoroughly, but it looks it is working. This explains why several opencl codes do actually work with these drivers and devices.

Needless to say, it is very frustrating to be forced to either use a 4 year old linux kernel and drivers or spend ages on questionable workarounds.

I would really appreciate if some driver developer could shed some light on this issue.

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skn1975
Adept I

Re: AMDGPU OpenCL Weird Results

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Allright. However, from the same github page I run a C++ example and it works fine! No problems at all. Examples failed for clFFT (C-style) and worked for ViennaCL (C++ style). If thats the case I am not worried as I code mostly in C++.

opencl-book-samples/src/Chapter_12/VectorAdd at master · bgaster/opencl-book-samples · GitHub

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rdemaria
Adept I

Re: AMDGPU OpenCL Weird Results

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It could be that

queue.enqueueMapBuffer

is doing the right thing, but I did have to use it with the fglrx driver.

At the moment I don't have the hardware to test if it is the case...

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skn1975
Adept I

Re: AMDGPU OpenCL Weird Results

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I have some updates for you:

a.) Your code in Github does not work for me!

b.) However, your solution in that code works

AMD SI Cards weird results · Issue #254 · ddemidov/vexcl · GitHub

In order to help other users, can you please provide a C-style API for your workaround? There are still many libraries that use C-style OpenCL notably clFFT and ViennaCL also

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