andies
Posts: 141
Joined: Mon Nov 11, 2013 8:12 pm
Location: Berlin

Load average versus CPU temp

Wed Apr 12, 2017 7:01 am

I have been using my RPi3 for a perl server called FHEM (just google it) and so I collected about 5500 data in a three minute interval from my Pi. I recorded CPU temp as well as load average and got the following pictures which shows a nice relation between the two.

I must remark that this RPi is idle most of the time, so it is only a few times getting above load 1. So, I do not know whether this relation holds in a different environment. Still, the equation reads

Code: Select all

CPU temp = 44°C + 10.2*load average 
Attachments
load-vs-temp Kopie.jpg
load-vs-temp Kopie.jpg (58.04 KiB) Viewed 615 times
raspberry B, Noir camera, Mac Book Air, iPhone, Bezzera

jahboater
Posts: 5632
Joined: Wed Feb 04, 2015 6:38 pm
Location: West Dorset

Re: Load average versus CPU temp

Wed Apr 12, 2017 7:24 am

Nice!

"Load average" is the run-queue length averaged over 1, 5, and 15 minutes.
So I a bit surprised the graph is at all linear - runnable jobs sitting in the queue use no resources and have no heating effect.

andies
Posts: 141
Joined: Mon Nov 11, 2013 8:12 pm
Location: Berlin

Re: Load average versus CPU temp

Wed Apr 12, 2017 7:37 am

True. On one hand the difference in CPU temp is still +- 5°C for a given load average (you see the very broad "line" filled with data). On the other hand if load is very low no ressources at all are used and if load starts climbing the processor picks up some work and hence some heat. This is my explanation.

The RPi sits next to a window with varying temperature (I suspect +- 10°C per day). So it would be better to plot it against load and the surrounding temperature. But I cannot do this at the moment, I have no recodings of the surrounding temp.
raspberry B, Noir camera, Mac Book Air, iPhone, Bezzera

Return to “Advanced users”