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Thread: Question about card clock frequencies

  1. #1
    Join Date
    Dec 2007
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    Default Question about card clock frequencies

    A quick question regarding clock frequencies on cards. I got a HD4850 and the BIOS has the following frequency presets:

    - Boot-up 625/993
    - "2D" 500/700
    - "3D" 750/1100

    With fglrx the card switches between the modes fine. With the radeon driver the xorg.0.log reports clocks of 625/993, so I take it the driver reads the boot-up frequencies from the BIOS. My question is, does the card ramp up to "3D clocks" as specified in the BIOS or does it simply read the first preset and ignores the rest? I ask because I'm about to make comparison benches for 3D performance between the two drivers and I would like to keep the card at the same frequencies for both tests.

  2. #2
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    Default

    Right now I believe the drivers stay with the default frequencies, ie 625/993 and do not dynamically change them, with the following exceptions :

    - the ForceLowPowerMode option sets the engine clock to 1/2 of default rather than default, ie ~322-ish/993 (I believe it also reduces the number of PCIE lanes used)

    - the DynamicPM option dynamically sets the engine clock to 1/4 of default, but only when the display is blanked by DPMS

    If you want the frequencies kept consistent for testing, you're gonna love the open source drivers

  3. #3
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    Default

    So basically I should underclock the card with Overdrive to 625/993 when I bench with fglrx then.

  4. #4
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    Default

    That sounds right.

  5. #5
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    Default

    Thanks. Results should be up by tonight .

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