Finding Out, How Many GPU Cores we have, Under Linux

One question which I see written about often on the Web, is how to find out certain stats about our GPU, under Linux. Under Windows, we had GUI-based programs such as ‘GPU-Z’, etc., but under Linux, the information can be just a bit harder to find.

I think that one tool which helps, is to have ‘OpenCL’ installed, as well as the command-line utility ‘clinfo’, which exists as one out of several packages, and as an actual, resulting command-name.

If we’re serious about programming our GPU, then having a GUI won’t help us much. We’d need to get dirty with code in that case, and then to have text-based solutions is suitable. But, if we’re just spectators in this sport, then two stats we may nevertheless want to know are:

1. How many GPU-Core-Groups do we have – since GPU-Cores are organized as Groups, and
2. How many actual Shader-Cores do we have in each Group?

Interestingly, the grouping of shader-cores, also represents how many vector-processors such GPU-computing tools as OpenCL see. And so, on the computer which I name ‘Klystron’, which is running Debian / Jessie, when typing in these commands as user, I get the following results:

dirk@Klystron:~$ clinfo | grep units
  Max compute units:                             4
  Max compute units:                             6
dirk@Klystron:~$ clinfo | grep multiple
  Kernel Preferred work group size multiple:     1
  Kernel Preferred work group size multiple:     64
dirk@Klystron:~$

This needs some explaining. On ‘Klystron’, I have the proprietary, AMD packages for OpenCL installed, since that computer has both an AMD CPU and a Radeon GPU. And this means that the OpenCL version will be able to carry out computing on both. And so I have the stats for both.

In this case, the second entries reveal that I have 6×64 cores on the GPU.

But if I try the same experiment on the recently-installed computer ‘Plato’, which is running Debian / Stretch, I only get partial results, with the error-message ‘Invalid Source':

dirk@Plato:~$ clinfo | grep units
=== CL_PROGRAM_BUILD_LOG ===
invalid source  Max compute units                               7
dirk@Plato:~$ clinfo | grep multiple
=== CL_PROGRAM_BUILD_LOG ===
invalid source  Preferred work group size multiple              invalid source
dirk@Plato:~$

It can tell me how many Groups I have – In the above box, some readers may have to scroll sideways to see this, but not how many Cores, in each group…

And the first-order explanation for why would be, that the ‘clinfo’ command is a mini-OpenCL program, which is written in C for the GPU, but which merely fetches the stats. Apparently, on ‘Plato’, some of the source-code written in ‘clinfo’ is not recognized by the OpenCL framework.

A closer look at the problem explains it better. On ‘Klystron’, my OpenCL installation is the proprietary AMD version of the packages – including ‘amd-clinfo‘, while on ‘Plato’, I only have the Mesa-Drivers, even for OpenCL, installed.

For this type of thing, of course it’s always better to be using the proprietary drivers. But in order to install the NVIDIA OpenCL Drivers on ‘Plato’, I’d also need to have several G.P. Graphics Drivers installed, including the proprietary as well as the generic ones, as I do on ‘Klystron’, and this means I’d need to install the ‘…alternatives…’ packages on ‘Plato’ as well, that presently allow me to switch back and forth between drivers, on ‘Klystron’.

For the moment, I think that would threaten what I have going with ‘Plato’ too much – which has been, a very stable experience. But this also means that with the Mesa Drivers alone, I cannot rely on doing any OpenCL computing, since even the demands of the generic ‘clinfo‘ package go beyond, what those OpenCL drivers can compile.

For now:

dirk@Plato:~$ clinfo
Number of platforms                               1
  Platform Name                                   Clover
  Platform Vendor                                 Mesa
  Platform Version                                OpenCL 1.1 Mesa 13.0.6
  Platform Profile                                FULL_PROFILE
  Platform Extensions                             cl_khr_icd
  Platform Extensions function suffix             MESA

  Platform Name                                   Clover
Number of devices                                 1
  Device Name                                     NVC4
  Device Vendor                                   NVIDIA
  Device Vendor ID                                0x10de
  Device Version                                  OpenCL 1.1 Mesa 13.0.6
  Driver Version                                  13.0.6
  Device OpenCL C Version                         OpenCL C 1.1 
  Device Type                                     GPU
  Device Profile                                  FULL_PROFILE
  Max compute units                               7
  Max clock frequency                             512MHz
  Max work item dimensions                        3
  Max work item sizes                             1024x1024x64
  Max work group size                             1024
=== CL_PROGRAM_BUILD_LOG ===
invalid source  Preferred work group size multiple              invalid source
  Preferred / native vector sizes                 
    char                                                16 / 16      
    short                                                8 / 8       
    int                                                  4 / 4       
    long                                                 2 / 2                  
    half                                                 0 / 0        (n/a)     
    float                                                4 / 4                  
    double                                               2 / 2        (cl_khr_fp64)                                                                             
  Half-precision Floating-point support           (n/a)                         
  Single-precision Floating-point support         (core)                        
    Denormals                                     No                            
    Infinity and NANs                             Yes                           
    Round to nearest                              Yes                           
    Round to zero                                 No
    Round to infinity                             No
    IEEE754-2008 fused multiply-add               No
    Support is emulated in software               No
    Correctly-rounded divide and sqrt operations  No
  Double-precision Floating-point support         (cl_khr_fp64)
    Denormals                                     Yes
    Infinity and NANs                             Yes
    Round to nearest                              Yes
    Round to zero                                 Yes
    Round to infinity                             Yes
    IEEE754-2008 fused multiply-add               Yes
    Support is emulated in software               No
    Correctly-rounded divide and sqrt operations  No
  Address bits                                    64, Little-Endian
  Global memory size                              1099511627776 (1024GiB)
  Error Correction support                        No
  Max memory allocation                           1099511627776 (1024GiB)
  Unified memory for Host and Device              Yes
  Minimum alignment for any data type             128 bytes
  Alignment of base address                       1024 bits (128 bytes)
  Global Memory cache type                        None
  Image support                                   No
  Local memory type                               Local
  Local memory size                               49152 (48KiB)
  Max constant buffer size                        65536 (64KiB)
  Max number of constant args                     15
  Max size of kernel argument                     4096 (4KiB)
  Queue properties                                
    Out-of-order execution                        No
    Profiling                                     Yes
  Profiling timer resolution                      0ns
  Execution capabilities                          
    Run OpenCL kernels                            Yes
    Run native kernels                            No
  Device Available                                Yes
  Compiler Available                              Yes
  Device Extensions                               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_byte_addressable_store cl_khr_fp64

NULL platform behavior
  clGetPlatformInfo(NULL, CL_PLATFORM_NAME, ...)  Clover
  clGetDeviceIDs(NULL, CL_DEVICE_TYPE_ALL, ...)   Success [MESA]
  clCreateContext(NULL, ...) [default]            Success [MESA]
  clCreateContextFromType(NULL, CL_DEVICE_TYPE_CPU)  No devices found in platform
  clCreateContextFromType(NULL, CL_DEVICE_TYPE_GPU)  Success (1)
    Platform Name                                 Clover
    Device Name                                   NVC4
  clCreateContextFromType(NULL, CL_DEVICE_TYPE_ACCELERATOR)  No devices found in platform
  clCreateContextFromType(NULL, CL_DEVICE_TYPE_CUSTOM)  No devices found in platform
  clCreateContextFromType(NULL, CL_DEVICE_TYPE_ALL)  Success (1)
    Platform Name                                 Clover
    Device Name                                   NVC4

ICD loader properties
  ICD loader Name                                 OpenCL ICD Loader
  ICD loader Vendor                               OCL Icd free software
  ICD loader Version                              2.2.11
  ICD loader Profile                              OpenCL 2.1
dirk@Plato:~$

Dirk