CODEWITHSUNDEEP
openclamd-gpu
Bram
Bram

Reputation: 8283

OpenCL reports half the expected compute units

I use OpenCL (under Ubuntu) to query the available platforms, which yields one platform, with

CL_PLATFORM_PROFILE: FULL_PROFILE

CL_PLATFORM_VERSION: OpenCL 2.1 AMD-APP (3143.9)

CL_PLATFORM_NAME: AMD Accelerated Parallel Processing

CL_PLATFORM_VENDOR: Advanced Micro Devices, Inc.

Which offers one device, which I query with:

cl_device_id device = devices[ j ];
cl_uint units = -1;
cl_device_type type;
size_t lmem = -1;
cl_uint dims = -1;
size_t wisz[ 3 ];
size_t wgsz = -1;
size_t gmsz = -1;
err = clGetDeviceInfo( device, CL_DEVICE_NAME, sizeof(name), name, 0 );
err = clGetDeviceInfo( device, CL_DEVICE_NAME, sizeof(vend), vend, 0 );
err = clGetDeviceInfo( device, CL_DEVICE_MAX_COMPUTE_UNITS, sizeof(units), &units, 0 );
err = clGetDeviceInfo( device, CL_DEVICE_TYPE, sizeof(type), &type, 0 );
err = clGetDeviceInfo( device, CL_DEVICE_LOCAL_MEM_SIZE, sizeof(lmem), &lmem, 0 );
err = clGetDeviceInfo( device, CL_DEVICE_MAX_WORK_ITEM_DIMENSIONS, sizeof(dims), &dims, 0 );
err = clGetDeviceInfo( device, CL_DEVICE_MAX_WORK_ITEM_SIZES, sizeof(wisz), &wisz, 0 );
err = clGetDeviceInfo( device, CL_DEVICE_MAX_WORK_GROUP_SIZE, sizeof(wgsz), &wgsz, 0 );
CHECK_CL
err = clGetDeviceInfo( device, CL_DEVICE_GLOBAL_MEM_SIZE, sizeof(gmsz), &gmsz, 0 );
CHECK_CL
if ( type == CL_DEVICE_TYPE_GPU )
        device_id = device;
printf( "  %s %s with [%d units] localmem=%zu globalmem=%zu dims=%d(%zux%zux%zu) max workgrp sz %zu", name, vend, units, lmem, gmsz, dims, wisz[0], wisz[1], wisz[2], wgsz );

Which gives me:

gfx1012 gfx1012 with [11 units] localmem=65536 globalmem=8573157376 dims=3(1024x1024x1024) max workgrp sz 256

The CL_DEVICE_MAX_COMPUTE_UNITS value of 11 worries me.

My system is equipped with the Radeon RX 5500 XT, which according to both AMDs website and Wikipedia is supposed to have 22 Compute Units.

Why does OpenCL report half the expected number, 11 Compute Units, instead of 22?

lspci reports:

19:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Navi 14 [Radeon RX 5500/5500M / Pro 5500M] (rev c5) (prog-if 00 [VGA controller])
        Subsystem: XFX Pine Group Inc. Navi 14 [Radeon RX 5500/5500M / Pro 5500M]
        Flags: bus master, fast devsel, latency 0, IRQ 83, NUMA node 0
        Memory at b0000000 (64-bit, prefetchable) [size=256M]
        Memory at c0000000 (64-bit, prefetchable) [size=2M]
        I/O ports at 7000 [size=256]
        Memory at c5d00000 (32-bit, non-prefetchable) [size=512K]
        Expansion ROM at c5d80000 [disabled] [size=128K]
        Capabilities: <access denied>
        Kernel driver in use: amdgpu
        Kernel modules: amdgpu

And the AMD GPU PRO driver was installed.

OpenGL vendor string: Advanced Micro Devices, Inc.
OpenGL renderer string: Radeon RX 5500 XT
OpenGL core profile version string: 4.6.14752 Core Profile Context 20.30
OpenGL core profile shading language version string: 4.60

Upvotes: 0

Views: 548

Answers (1)

ProjectPhysX
ProjectPhysX

Reputation: 5754

For AMD RDNA GPUs, OpenCL with CL_DEVICE_MAX_COMPUTE_UNITS reports the number of dual compute units (see the RDNA whitepaper, pages 4-9). Each dual compute unit contains 2 compute units, as the name suggests. So your hardware and driver installation is fine.

Upvotes: 6

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