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I have a new Acer Aspire laptop (bought in February, now running Xubuntu 17.04), and when the power is plugged in, the CPU frequency is always 3.5 GHz, but when it is not plugged in, 2.7 GHz. So it saves some power.

It would be great if this could be automatically adjusted, as with 2.7 GHz, the battery is drained in just 2 hours.

My old laptop (with Xubuntu 16.04, also an Acer Aspire) automatically throttled down to 400 MHz when idle.

Edit 4: I have removed the previous edits, and my handmade logging tool caught an instance of this happening:

Tue Apr 18 12:56:36 2017 CPU MHz:               651.190
Tue Apr 18 12:56:46 2017 CPU MHz:               3491.186
Tue Apr 18 12:56:56 2017 CPU MHz:               984.484
Tue Apr 18 12:57:06 2017 CPU MHz:               799.871
Tue Apr 18 12:57:16 2017 CPU MHz:               3499.859
Tue Apr 18 12:57:26 2017 CPU MHz:               3499.859
Tue Apr 18 12:57:36 2017 CPU MHz:               3499.859
Tue Apr 18 12:57:46 2017 CPU MHz:               3500.036

...continuing with 3499.xxx and 3500.xxx, and very rarely 34xx.xxx.

After carefully comparing the pstree output with wdiff, I have not seen any different processes running before and after it happens.

user258532
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  • CPU should auto-adjust its frequency. Can you post any evidence at all to your observation. – mikewhatever Apr 15 '17 at 14:12
  • Which CPU frequency scaling driver and which governor are you using? Do: cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_driver and cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor – Doug Smythies Apr 15 '17 at 14:36
  • see edits above – user258532 Apr 15 '17 at 15:02
  • And so, after a re-boot it is working properly, right? – Doug Smythies Apr 15 '17 at 15:15
  • Yes... scratching head... – user258532 Apr 15 '17 at 16:41
  • I can only guess that the governor was somehow performance before. – Doug Smythies Apr 15 '17 at 18:24
  • Now it's happening again, after using Firefox, Thunderbird and some terminal windows. Again stuck at 3.5 GHz even when, according to {htop}, the cores are largely idle. Are there some hidden processes? – user258532 Apr 15 '17 at 20:25
  • Check if the governor changed. – Doug Smythies Apr 15 '17 at 20:38
  • It's always intel_pstate, and the setting is always powersave. I checked that. – user258532 Apr 16 '17 at 13:15
  • Then the suggested next step would be to acquire a trace to help figure out what is going on. There a cool new script to help with trace data, but it is only in the kernel 4.11 source tree so far. We can move to chat to continue, or wait for input from someone else. – Doug Smythies Apr 16 '17 at 14:24
  • I wrote a little script to watch that issue. I've pasted it in the original question. I suspect that CPU freq is stuck at the maximum after ´rdiff-backup´ had to clean up an interrupted backup increment, which is very CPU intensive and also uses lots of RAM. – user258532 Apr 17 '17 at 12:41
  • Some more research: Disabling "Pre-released updates (zesty-proposed)" does not solve the problem either. Neither does a fresh install. Sometimes, the laptop lasts > 4 hours with a "sane" CPU frequency, at other times, it gets stuck at 3.5 GHz just after five minutes. – user258532 Apr 23 '17 at 10:03

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