[Solved] Deactivate Cores

[Si3Ste]

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

[jdb]

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

Where N is in range 1 to 4.

[jamesh]

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!

[pluggy]

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.

[Si3Ste]

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

[jdb]

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.

[mkirk]

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]

Try replacing maxcpus=n with isolcpus=n. All CPUs get the same clock, but temperature under load should definitely reduce with <4 CPUs online.