Arch Linux

Frosted

Member

Registered: 2014-04-18

Posts: 20

CPU Downclocking

Sort of to help others:

I've been overclocked for years at 4.7Ghz with EIST and all the rest disabled. In Windows my clock was never dynamic. 4.7 every day all day. I noticed that on this Arch install my CPU's clock was dynamic. I even went as far as reflashing the BIOS to try to correct this. Turns out this is something that came with one of the recent kernel updates. (yeah?) If you would like to increase your minimum clock, edit the percentage in the file /sys/devices/system/cpu/intel_pstate/min_perf_pct.

Now, I didn't notice this downclocking until I installed a monitor widget. So perhaps it's a bit of a waste to have my CPU run at full speed 24/7. I think I'll play with the interval times. I don't like how there's a bit of a delay between demand on CPU and when it actually increases the clock. So I'll work on that later. For now I upped the minimum clock to 50%.

https://www.kernel.org/doc/Documentatio … ernors.txt

Last edited by Frosted (2014-04-28 09:43:58)

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ewaller

Administrator

From: Pasadena, CA

Registered: 2009-07-13

Posts: 19,772

Re: CPU Downclocking

Running a processor at full speed under a light load is a waste of (high order) energy resulting only in converting that high order energy into low order energy (heat).
Heat takes life out of your processor, increases the heat load on the room (good in winter, bad in summer).  So much so that, during times where you don't need to heat the room by burning fossil fuels, you might even notice the difference on your power bill.  If you reduce the load by 20W and pay US$0.16/kWh, you save about $26/year on the power to the processor alone.  Heat load costs are harder to calculate on the back of an envelope.

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Gusar

Member

Registered: 2009-08-25

Posts: 3,605

Re: CPU Downclocking

The CPU's frequency is constantly changing in millisecond intervals. And the impact on performance is negligible. Don't look at desktop widgets and think you know what's going on with the CPU. Use proper tools, like powertop and turbostat. They'll tell you how often and what periods of time the processor spent in which state. An interesting hint - in C3-C7 states, where your CPU will be most of the time, the CPUs frequency is 0! Read this fore more info: https://plus.google.com/114657443111661 … Ln9T4ehywL

Disabling EIST is nonsense. You're heating up the CPU (decreasing its longevity) and increasing your power bill for no reason whatsoever.

Frosted

Member

Registered: 2014-04-18

Posts: 20

Re: CPU Downclocking

Since the kernel is doing this, if I enabled EIST, woundn't there then be two mechanisms adjusting the clock? I'm thinking I should stick to one.

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I have a knack for having a knack, but know nothing too well.

Gusar

Member

Registered: 2009-08-25

Posts: 3,605

Re: CPU Downclocking

The kernel governs EIST. It not two things doing their thing, it's one thing telling the other how to behave.

Frosted

Member

Registered: 2014-04-18

Posts: 20

Re: CPU Downclocking

Then how am I downclocking with EIST disabled? Same BIOS settings I had in other OS installations and the clock never moved.

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I have a knack for having a knack, but know nothing too well.

Gusar

Member

Registered: 2009-08-25

Posts: 3,605

Re: CPU Downclocking

The kernel overrides the bios?

Frosted

Member

Registered: 2014-04-18

Posts: 20

Re: CPU Downclocking

Yeah.

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I have a knack for having a knack, but know nothing too well.