I have put some of this stuff on IRC, but for those who missed and to have
responses I can remember in one place... I have moved it here.
I have added the ability to select either Performance or Powersave as the
CPU governor to ubuntustudio-controls. This just works at this point.
Feel free to download and install or add this ppa:
https://launchpad.net/~ubuntustudio-dev/+archive/ubuntu/autobuild
to try it out. (I prefer to download the *.deb and dpkg -i it :)
The part I would like to do next is to have a second checkbox that turns
on persistance so this setting will survive reboot. cpufrequtils would
make this rather easy as it reads a file in /etc/defaults/ to see what
governor it should use for this system. Unfortunately, there is a second
init script, ondemand that waits for 60 seconds and forces the ondemand
governor at that point undoing whatever cpufrequtils does :P
So, my next thought is that we can leave cpufrequtils set to performance
at boot. Then ubuntustudio-controls can run:
update-rc.d ondemand disable
To set the next boot to performance, and:
update-rc.d ondemand enable
to set the next boot to ondemand/powersave
This article:
http://www.phoronix.com/scan.php?page=article&item=linux-47-schedutil&num=1
Seems to suggest intel p-state governors may have problems (at least in
4.7, we use 4.4).
Also, it seems that powersave != powersave.
At least on my machine, powersave does not do what the docs say (run at
lowest available frequency). My 32 bit system does this, my 64bit system
does not. So the ubuntu default of use ondemand if available or powersave
otherwise makes sense. If ondemand is available, powersave is bad, but if
ondemand is not available powersave is the only other possibility and does
ramp up speed.
More research on power use with performance vs ondemand. It appears that
on a system that has an effective idle state, performance uses less power
because it enters idle state much faster than ondemand. See:
http://www.phoronix.com/scan.php?page=news_item&px=MTM3NDQ
Despite what:
https://wiki.archlinux.org/index.php/CPU_frequency_scaling
says, performance on my pstate machine does not "provide dynamic scaling"
(thankfully). This will be something to watch though as the first article
I pointed to seems to indicate kernal 4.7 has bad performance governor
stats. This may be because I have "Boost" turned off in BIOS. Turning
Boost on may cause speed changes to cope with heat.
I have also noticed that having one core at a different speed than the
other cores actually generates more heat (more heat means more power
used). That is setting the governor to userspace and manually setting all
cores to full speed runs cooler than lowering the speed of one of those
cores. So there will be some loss using ondemand but if the speed on that
one core is low enough, that may make up for this.
So it appears that -settings can add cpufrequtils to /etc/default/ with a
setting to performance. This will at least speed up boot speed.
-controls should be able to set performance or ondemand/powersave in the
same way as /etc/init.d/ondemand does (try ondemand but fall back to
powersave)
As I find time in the next few weeks I will do more work on -controls and
-settings.
--
Len Ovens
www.ovenwerks.net
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