Dear Powertop Team, I have noticed that powertop changes the frequency set by the userspace governor to the minimum available frequency. This is caused by abstract_cpu::wiggle that touches the {min,max}_freq. By doing so, it also narrows down the scaling_setspeed setting within the min-max-range, but it is not reset upon restoring max_freq. To illustrate what is happening behind the scenes: $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_{min,max,cur}_freq 1200000 2901000 2000000 $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_{governor,setspeed} userspace 2000000 $ echo 1200000 | sudo tee /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq 1200000 $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed 1200000 (Tested with Linux 4.4.0-21 Ubuntu) Attached is a patch that resets the setspeed value if it was set to a numeric value before the wiggle. Please note that I don't really understand what you are trying to achieve with the wiggle in the first place. It seems for instance that this doesn't do anything if max_freq == min_freq.

Best Regards, Thomas Ilsche

> > > > Please note that I don't really understand what you are trying to > > achieve with the wiggle in the first place. It seems for instance > > that this doesn't do anything if max_freq == min_freq. We need to force a perf event at the beginning of the sampling period. That's the only way the code can determine the starting frequency. There may be other/better ways to do this. Patches, input always welcome.

Hi Joe, seems the patch was already applied successfully: https://github.com/fenrus75/powertop/commit/1636ce2c01d9bba024f2840f114b6...

On 2016-07-26 19:27, Joe Konno wrote: > Hi Thomas, > > I cannot apply your diff to either the v2.8 tag or master. Could you > rebase it atop master and re-submit? Thanks! > > PS: I'll address the question about wiggle particulars separately. > To be perfectly honest I have some digging to do. ^_^ > > On Thu, 21 Jul 2016 12:13:17 +0200 > Thomas Ilsche <thomas.ilsche(a)tu-dresden.de&gt; wrote: > >> Dear Powertop Team, >> >> I have noticed that powertop changes the frequency set by the >> userspace governor to the minimum available frequency. >> >> This is caused by abstract_cpu::wiggle that touches the >> {min,max}_freq. By doing so, it also narrows down the >> scaling_setspeed setting within the min-max-range, but it is not >> reset upon restoring max_freq. To illustrate what is happening >> behind the scenes: >> >> $ >> cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_{min,max,cur}_freq >> 1200000 2901000 >> 2000000 >> $ >> cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_{governor,setspeed} >> userspace 2000000 >> $ echo 1200000 | sudo >> tee /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq 1200000 >> $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed >> 1200000 >> >> (Tested with Linux 4.4.0-21 Ubuntu) >> >> Attached is a patch that resets the setspeed value if it was set >> to a numeric value before the wiggle. >> >> Please note that I don't really understand what you are trying to >> achieve with the wiggle in the first place. It seems for instance >> that this doesn't do anything if max_freq == min_freq. >> >> Best Regards, >> Thomas Ilsche >> >