Arch Linux

McFlow

Member

Registered: 2010-04-17

Posts: 58

Ondemand Governor steadily changing frequency

Hello,
I installed cpufrequtils and set the governor to ondemand. The up_threshold is set to 95%. If I change window focus, open a new window or change workspace the xfce-cpufreq-plugin shows that the frequency goes up to max for a short moment. This happens quite often. I don't think it's healthy for the cpu to have the frequency changed so often.
top lists no process that uses more than 4% cpu. My cpu is a AMD II X3 435.
Even when I am unpacking a hughe archive it changes very frequently.

watch grep \"cpu MHz\" /proc/cpuinfo

Shows some changes as well. But not as fast as the panel applet. Still I think it's not healthy for the cpu. But I'm not sure if it has influence on the lifetime.
I can reproduce that on my laptops Intel i3-330m.
Both systems are up to date and run archlinux 64 bit with xfce.
I'm not sure if it's just a display bug. I did not find any reports so far.

I wonder if this just is done to shorten calculations time so that the cpu can go to "sleep mode" as fast as possible?

demian

Member

From: Frankfurt, Germany

Registered: 2009-05-06

Posts: 709

Re: Ondemand Governor steadily changing frequency

That behaviour is intended and very efficient.

The ondemand governor jumps the processor to full performance once demand reaches a certain threshold. It then drops back to lower performance states when the work is exhausted. This allows a return to idle in as short a timeframe as possible. The reason to prefer ondemand over performance is that very short bursty workloads will prevent the CPU from entering deep C states anyway, but do not generally benefit from being run at the higher CPU speeds. Not raising the processor clock for this workload can save some energy.

Source: http://www.codon.org.uk/~mjg59/power/go … tices.html

Regards,
demian

Last edited by demian (2010-05-09 20:37:14)

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DonVla

Member

From: Bonn, Germany

Registered: 2007-06-07

Posts: 997

Re: Ondemand Governor steadily changing frequency

Try the "conservative" governor.
The CPU takes no harm from this frequency changes. It is designed for this.

PS: BTW, a good measure for unexpected activity of the CPU is the temperature.
If the temp remains high for longer time while the CPU switches the frequency often, this can be an indicator for something broken.
If the temp remains constant, that's ok (I guess ).

Last edited by DonVla (2010-05-09 20:40:19)

Wintervenom

Member

Registered: 2008-08-20

Posts: 1,011

Re: Ondemand Governor steadily changing frequency

According to the kernel/CPUFreq documentation, the conservative governor is best for AMD CPUs:

If you have a desktop machine then you should really be considering the 'ondemand' governor instead, however if you are using a laptop, PDA or even an AMD64 based computer (due to the unacceptable step-by-step latency issues between the minimum and maximum frequency transitions in the CPU) you will probably want to use this governor.

McFlow

Member

Registered: 2010-04-17

Posts: 58

Re: Ondemand Governor steadily changing frequency

Okay, thanks a lot.
So no need to worry about my CPU.

Thanks for the information!

ominide

Member

Registered: 2009-10-11

Posts: 15

Re: Ondemand Governor steadily changing frequency

Also consider the fact that the CPU time unit reference for perspective is in the order of nanoseconds.  Sorry for jumping in late but thats the other thing about govenours. And system load, also correct me if I'm wrong but top doesn't delinate as to per core its total system so that 4% per process on your X3 could be 12% of one core, not huge but the over head of starting a new process / window (assuming new process) is pretty significant to the kernel.