Something is Wrong with my XPS 15 When I try to undervolt

Discussion in 'Dell XPS and Studio XPS' started by EORUCIGN, Jul 10, 2018.

  1. Danishblunt

    Danishblunt Notebook Virtuoso

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    Good decision.
     
  2. EORUCIGN

    EORUCIGN Notebook Consultant

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    It seems like my unit doesn't have thermal throttling, but hard power limit throttling because even when I ran prime95, there was no sign of thermal throttling according to XTU.
     
  3. Eason

    Eason Notebook Virtuoso

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    Set it to "save settings now" in FIVR
     
  4. MSIX

    MSIX Notebook Enthusiast

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    I'm currently testing the i9 8950hk in my Xps and have found that it does not like -150mv core and will cause my system to hang.

    Currently trying -145mv core amd -142mv cache with 0 Speed Shift EPP
     
  5. pressing

    pressing Notebook Deity

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    I think you need to match undervolt of CPU core & CPU cache.

    -150mv is a pretty aggressive undervolt. Also, each chip is different so you can search for undervolt ranges that worked for others. But you can't trust that the higher numbers were tested in more extreme conditions so may not be very stable.

    Normally you will see people test with very conservative undervolts, say -100mv or -110mv and run some tough benchmarks for a few hours; maybe some games. If no issues maybe bump up in -10mv increments and full testing again. Then once issues arise drop back -10mv or -20mv.
     
  6. MSIX

    MSIX Notebook Enthusiast

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    Yes I have a feeling my values of -145 and -142 is too much. When running Realbench stress test my Dimm temp goes through the roof 90c and starts underclocking my cpu significantly. System then blue screens.
     
  7. pressing

    pressing Notebook Deity

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  8. EORUCIGN

    EORUCIGN Notebook Consultant

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    I am still testing my undervolt, and it's currently -160mv. What's funny is when I was using -190mv, it passed the prime95 test, but when I played outlast 2, it immediately showed a blue screen.
     
  9. pressing

    pressing Notebook Deity

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    You need to do a variety of stress tests and your own usage to see how it holds up. Your stress tests should be for several hours also.

    Your gaming pushes the power module hard due to GPU use. Also has different CPU demands. Bottom line is that you should not expect to run undervolt near -190mv if you are looking for reliability.
     
  10. custom90gt

    custom90gt Dellerator Moderator

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    Typically a CPU will work fine at a decent voltage when at it's full turbo boost due to the way the voltage tables are setup. -160mv isn't much when you're at a much higher voltage. The problem is when the system lowers the clockspeed the -160mv isn't stable because it's running at a much lower voltage due to the voltage table.

    An easy way to test this is to set your undervolt, start prime95 for a couple of minutes, and then exit prime95. Do that a couple of times and you'll probably BSOD (for sure at -200mv). That's why I recommend AIDA64 because it varies the CPU speed (and the voltages that it runs at).

    Hopefully that makes sense.

    Here is a quick example with just random numbers that I made up.
    Say at max turbo the cpu voltage table says use 1v so 1-.016=0.84v
    But at min clock speed the voltage table says use .4v so 0.4-0.16=0.24v
     
    Woodking and pressing like this.
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