undervolting (e.g. skylake) in linux

Discussion in 'Hardware Components and Aftermarket Upgrades' started by conker_ts, Aug 13, 2017.

  1. tincmulc

    tincmulc Notebook Enthusiast

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    Yeah, I now wish I took the time to thoroughly read the thread before posting my mostly wrong conclusions about the oc mailbox.
    On the other hand it feels good that we eventually came to the correct answer (well at least as far offset undervolting is concerned) without help.
     
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  2. Vasudev

    Vasudev Notebook Virtuoso

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    I did undervolt to -120.2mV using TS ini file. Temps reduced by 2C. 38C -> 36C. Maybe because I used powertop to calibrate power usage and optimise the temps by 10C, earlier it idles at 48C. Anyone had luck in manipulating the fan speed on Alienware on Linux?
     
  3. leeloyd

    leeloyd Notebook Consultant

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    Skylake and Kabylake aren't that easy to OC/UV.

    I followed the hints from there :
    https://forums.anandtech.com/threads/what-controls-turbo-core-in-xeons.2496647/page-40#post-38971756

    If i boot straight in Linux, MSR0x150 seems to have some contexts locked.

    Code:
    $ sudo wrmsr 0x150 0x8000000100000000
    $ sudo rdmsr 0x150
    0000000000000753
    
    $ sudo wrmsr 0x150 0x8000001000000000
    $ sudo rdmsr 0x150
    0
    If I boot first in Windows, than reboot in Linux. I can access all context (CPU,Cache,etc...).

    Code:
    $ sudo wrmsr 0x150 0x8000000100000000
    $ sudo rdmsr 0x150
    0000000000000753
    
    $ sudo wrmsr 0x150 0x8000001000000000
    $ sudo rdmsr 0x150
    0000000000000024
    CPU : I7 6820HK.

    Edit : Never mind, setting an undervolt works. Even when I boot straight too Linux.

    Ok next step : OC.
     
    Last edited: Sep 3, 2017
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  4. conker_ts

    conker_ts Notebook Enthusiast

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    That's strange, the read command looks corrent. So what was the problem exactly ?
    I'd still guess, this write-read cycle is not that stable, b/c there is too much time/ many cpu cycles in between ...

    Did you mean undervolt ? ^-^

    Hm, that's strange ...
    Does Powertop have similar CPU Package Power field as in TS/Aida ?
    This should be probably documented in the Intel Docs, which MSR to read for the current Power drain in Watts. Then we may have a better indication, if the UV did work ...
     
  5. alfazaz

    alfazaz Newbie

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    Oups, sorry : yes ! I undervolt... It works very well.
     
  6. Vasudev

    Vasudev Notebook Virtuoso

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    Install powertop using synaptic pkg manager from ubuntu repos.
     
  7. leeloyd

    leeloyd Notebook Consultant

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    Maybe because the oc_mailbox, wasn't already used to change OC parameters. In Windows, I thing TS or xtu must change ratio to default at start-up.
     
    Last edited: Sep 8, 2017
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  8. ngoonee

    ngoonee Newbie

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    I've got an i7-8550 based laptop (HP Envy 13), doesn't seem like anyone has tried this out on the Kaby Lake Refresh chips yet? Still have my windows install (shrunk considerably) here, and running Arch Linux. Will be following the guide, but is there anything I can check to see if the MSR codes have changed between Kaby Lake and Kaby Lake R?
     
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  9. Vasudev

    Vasudev Notebook Virtuoso

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    Did you try ThrottleStop first?
     
  10. ngoonee

    ngoonee Newbie

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    Yes, am playing with that now. Certainly quite a bit of headroom for undervolting, -50mV without artifacts so far.

    EDIT: Okay seem to have reached the safe limit at -110mV, -120mV gave me the BSOD. Running Prime95 now, will leave it for the rest of the workday.

    The ThrottleStop.ini contents are as mentioned on https://github.com/mihic/linux-intel-undervolt

    FIVRVoltage00, FIVRVoltage10, and FIVRVoltage20 contain the changes I made (CPU Core, Intel GPU, CPU Cache). So no change from skylake/kaby lake I think.

    Also just did a quick check of the manual offset calculation, and it was spot on.

    Will report back when I've done Prime95 stress testing and get round to applying settings in Linux.

    EDIT2: Well got an error after a few hours on -110, now on -105. Applied it to Linux, i7z does show a clear drop in VCore. mprime seems to run slower compared to on Windows though (getting 1.6GHz rather than the 2.4GHz I was getting under Windows). Would chalk that up to different boost settings. At least there's a clear VCore change and my theoretical power usage should be lower.
     
    Last edited: Oct 26, 2017
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