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I own a Dell XPS 9370 laptop with an i7 8550U.

I recently noticed, that my performance decreases quite significantly when my battery percentage drops under 20%. This especially visible on GNOMEs animations, which start to get pretty laggy. This happens in all Ubuntu versions from 18.04 to 19.10 I tested.

I tried to investigate a bit and observed that my CPU frequency does not scale up properly anymore, it does not reach the max frequency of my processor (4 GHz) by far after my battery life falls under 20%. When running with over 20%, it scales properly up to the 4 GHz.

Setting the CPU governor to performance removes that impact but is obviously not a solution, as that has a serious impact on the battery life.

So all in all it feels like a power saving feature of the governor. Is there a possibility to turn it off or move the battery percentage that kicks in? Maybe some kernel parameter?
Any additional ideas to solve that problem?

Cheers in advance

P.S: I uninstalled all additional power saving tools I know of (tlp etc.), but that did not help either.

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  • This is not a kernel thing, nor anything to do with any governor. As far as I know, it is a Dell thing. When under 20% battery what do you get for cat /sys/devices/system/cpu/intel_pstate/max_perf_pct and cat /sys/devices/system/cpu/intel_pstate/no_turbo? Nov 11, 2019 at 22:41
  • @DougSmythies Good to know. Those are the values for over 20%: cat /sys/devices/system/cpu/intel_pstate/max_perf_pct returns 100 and cat /sys/devices/system/cpu/intel_pstate/no_turbo returns 0. I will add those for under 20% after my battery life dropped... Nov 11, 2019 at 22:53
  • Low battery situations dictate shutting off powerr to subsystems. Then when they are accessed power up introduces more latency. That's my guess. Nov 11, 2019 at 23:04
  • Dell forces "clock modulation" via the BIOS under some circumstances, this might be one of them. To determine for certain see here. And note: you may find around here comments from me saying "the intel_pstate CPU frequency driver is fundamentally incompatible with clock modultion". That is no longer true, but it will limit your max frequency. Nov 11, 2019 at 23:10
  • @InvisibleShadowGhost : I missed that you mentioned "for over 20%". Only look into clock modulation if the other numbers stay after battery < 20%. Nov 12, 2019 at 0:43

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