Si3Ste
Posts: 3
Joined: Mon Feb 09, 2015 4:00 pm

[Solved] Deactivate Cores

Mon Feb 09, 2015 4:02 pm

Hi all,

I own some Raspberry 2 since last end of Week and I believe that 4 cores are too much for me :)

Is there is way to deactivate/park some of the cores ( for me 2 is enough ) ? It will reduce power consumption and heat.


Regards

Si3Ste
Last edited by Si3Ste on Fri Feb 13, 2015 3:52 pm, edited 1 time in total.

jdb
Raspberry Pi Engineer & Forum Moderator
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Re: Deactivate Cores

Mon Feb 09, 2015 4:39 pm

Edit /boot/cmdline.txt and add maxcpus=N

Where N is in range 1 to 4.
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jamesh
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Re: Deactivate Cores

Mon Feb 09, 2015 4:40 pm

I would be interested to know how much that reduces current draw. I suspect not a lot, but waiting for someone to work out the figures!
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pluggy
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Re: Deactivate Cores

Mon Feb 09, 2015 4:47 pm

http://raspi.tv/2015/raspberry-pi2-powe ... easurement

This suggests 40mA per fully loaded core, But getting it to fully use all the cores is tricky. Disabling 2 of the cores would make little or no difference in the real world I reckon.
Don't judge Linux by the Pi.......
I must not tread on too many sacred cows......

Si3Ste
Posts: 3
Joined: Mon Feb 09, 2015 4:00 pm

Re: Deactivate Cores

Fri Feb 13, 2015 2:14 pm

Well, tried, it works but don't seems to change manything. not even 2-3 degree less on my tests

jdb
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Raspberry Pi Engineer & Forum Moderator
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Re: Deactivate Cores

Fri Feb 13, 2015 3:39 pm

The cores are being clock-gated when not in use (either not being used by Linux, or no active tasks running), therefore you will still have static leakage dissipation. Essentially the maxcpus=N directive limits the maximum power consumption by proxy, with negligible effect on idle power consumption.
Rockets are loud.
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mkirk
Posts: 64
Joined: Tue Mar 06, 2018 4:21 pm

Re: [Solved] Deactivate Cores

Tue Aug 20, 2019 9:25 pm

Questions:
1) For maxcpus=4, if one CPU core is at 100% load and running at max clock, e.g. 1.2 GHz.
Are the other 3 cores (idle) also clocked at 1.2GHz? Or do these idle cores run at min clock , e.g. 600 MHz?

2) Does an idle core running at max clock use same power as a core with 100% load?

I am guessing yes, since my testing with stress and sysbench for 2 cores gives similar results (temperatures) as 1 and 4 cores.

jdb
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
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Re: [Solved] Deactivate Cores

Wed Aug 21, 2019 4:02 pm

Try replacing maxcpus=n with isolcpus=n. All CPUs get the same clock, but temperature under load should definitely reduce with <4 CPUs online.
Rockets are loud.
https://astro-pi.org

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