power saving

Xen list at xenhideout.nl
Mon Dec 11 17:31:59 UTC 2017


Colin Law schreef op 11-12-2017 17:26:

> Interesting. Do those savings still exist when the screen is asleep

I am almost a 100% certain but as I did not check I would have to 
uninstall the nvidia driver again which I rather would not.

> and the processor is not working hard?

Yes.

The CPU can idle at 800MHz but runs maximum 2600MHz.

The default profiler activated by the Linux kernel is apparently 
"performance" which never lowers the frequency.

The "cpufrequtils" package does nothing other than set the profiler at 
boot and provide utils to set and read it.

The "ondemand" profiler switches between 800 and 2600 in a few steps.
The "conservative" profiler does the same but slower.
The "powersave" profiler keeps it at 800.

I don't know why the default was (and is) performance.
But it disables what you could call Cool'n'Quiet.

Phoronix showed benchmarks between Nouveau and Nvidia, and showed Nvidia 
having lower power consumption, so I tried.

This is a Phenom II cpu and Nvidia GTX 950.

I have no clue why this was not installed by default on Kubuntu, because 
Debian 8 does have it (cpufrequtils).

The phoronix benchmarks showed a difference of about 8W I think so this 
does coincide.

I'm sorry I cannot check the "poweroff" state but I am pretty certain it 
is constant.

(( Nouveau cannot or does not by default set "performance states" and 
keeps the GPU running at the "boot" frequency (which is very low) but 
still consumes more power )).

This is Phoronix:

https://www.phoronix.com/scan.php?page=article&item=fedora_nouveau_power&num=2

The low point of the graph is DPMS "power off".

His test is on a laptop and notices a 5W difference in "power off" 
between Nouveau and nVidia.

Mine is a 90W discrete GPU, so for me the difference is larger.



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