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Sun Dec 11 16:18:29 EST 2016

revisit

on the Radeon HD 7800 Pitcairn
[    86.336] (--) RADEON(0): Chipset: "PITCAIRN" (ChipID = 0x6811)

This would be OpenCL.

https://anteru.net/blog/2012/11/03/2009/

http://stackoverflow.com/questions/21522554/how-to-setup-opencl-on-amd-videocard-with-opensource-driver

glxinfo->
OpenGL renderer string: Gallium 0.4 on AMD PITCAIRN (DRM 2.43.0 / 4.6.0-1-amd64, LLVM 3.8.1)

https://packages.debian.org/sid/mesa-opencl-icd
# apt-get install mesa-opencl-icd

https://laanwj.github.io/2016/05/06/opencl-ubuntu1604.html

see also git/opencl archive

tom@zoe:~/opencl$ ./devices.elf
1. Platform
  Profile: FULL_PROFILE
  Version: OpenCL 1.1 Mesa 13.0.2
  Name: Clover
  Vendor: Mesa
  Extensions: cl_khr_icd
1. Device: AMD PITCAIRN (DRM 2.43.0 / 4.6.0-1-amd64, LLVM 3.9.0)
 1.1 Hardware version: OpenCL 1.1 Mesa 13.0.2
 1.2 Software version: 13.0.2
 1.3 OpenCL C version: OpenCL C 1.1 
 1.4 Parallel compute units: 20



What's the difference between compute units (20) and stream cores (see wikipedia: 1024-1280)
https://community.amd.com/thread/166930
https://community.amd.com/community/devgurus


CU is roughly equivalent to an independent CPU.
Each CU is subdivided into stream cores, programmed using SIMT.

GCN = graphics core next
https://en.wikipedia.org/wiki/Graphics_Core_Next

The Graphics Core Next (officially called "Southern Islands")
microarchitecture combines 64 shader processors with 4 TMUs and 1 ROP
to a compute unit (CU).

Each Compute Unit consists of:
- a CU Scheduler
- a Branch & Message Unit
- 4 SIMD Vector Units (each 16-lane wide)
- 4 64KiB VGPR files
- 1 scalar unit
- a 4 KiB GPR file
- a local data share of 64 KiB
- 4 Texture Filter Units
- 16 Texture Fetch Load/Store Units
- a 16 KiB L1 Cache.

Four Compute units are wired to share an Instruction Cache 16 KiB in
size and a scalar data cache 32KiB in size. These are backed by the L2
cache.

A SIMD-VU operates on 16 elements at a time (per cycle), while a SU
can operate on one a time (one/cycle). In addition the SU handles some
other operations like branching.

This seems interesting:
http://developer.amd.com/wordpress/media/2013/07/AMD_Accelerated_Parallel_Processing_OpenCL_Programming_Guide-rev-2.7.pdf




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