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Why discrete GPU works at the same low frequency as the integrated GPU in APU?

Question asked by tohwh on Jul 31, 2013
Latest reply on Aug 2, 2013 by himanshu.gautam

Hello, everyone

 

  Before describing my problem, I would like to provide my platform information first:

 

 

    OS:

          Windows 7 64 bit

 

    System:

          Motherboard:    GA-A75M-UD2H

          Processor:         A8-3850 (with Radeon HD 6550D)

          Video Card:       Radeon HD 7850 (MSI R7850 HAWK 2G)

 

    Softwares:

          Catalyst 13.4

          AMD APP v2.8.1

          Visual Studio 2012

 

  When I run clinfo.exe from Windows console, it could successfully detect 3 OpenCL devices, namely a discrete GPU (the Radeon HD 7850), an integrated GPU (the Radeon HD 6550D), and a CPU, in sequence. All information retrieved seems to be right except that the ‘Max Clock Frequency’ of the discrete GPU is 600 MHz, not the default 980 MHz. The retrieved value is the same with the integrated GPU. If I change the ‘Init Display First’ in BIOS settings from ‘Onboard’ to ‘PEG’, reboot and run clinfo.exe again, it will retrieve the correct max clock frequency for the discrete GPU. To verify what I observed, I wrote a short C program to query the devices the CL_DEVICE_MAX_CLOCK_FREQUENCY by calling clGetDeviceInfo, and I got the same results. Why does the discrete GPU works at the same low frequency as the integrated GPU? I intend to use the discrete GPU as my scientific computing engine. It will be frustrating if it cannot work full-powered. Is there someone could help me fix this problem?

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