Locked computer gets very hot despite no CPU-intensive tasks running

I'm using Ubuntu 15.10 on my HP ProBook 6470b laptop. When I lock it and walk away from my desk it often gets very hot, very quickly.

Here's a screenshot of Psensor graph which shows the problem, the temperature started to raise just after I locked the device.

Answer: Yeah, it was compiz. No, I don't yet know how to fix it

I was trying to find the root cause of this, but I'm running out of the ideas. More details about my setup:

• This is my work computer, it runs in Windows-based corporate environment.
• The computer is usually docked into station, but the problem also appears when its undocked.
• The computer starts to cool down when I unlock it, without any additional actions.
• No external devices (except Logitech mouse) are connected.
• I'm using Compiz with Unity, pretty much default setup (I enabled some compiz plugins though, I love them).

So far I tried:

• Installed a few power-monitoring and controlling tools, like cpufrequtils and tlp. I'm using powersave CPU governor.
• Compiled libstdc++ with patch for GCC Bug 68921 since it was suggested that if fixes the issue I'm having
• Turned off VBlank sync and enabled forced full screen redraw for compiz, as suggested in another report of (probably) the same bug

None of that helped.

Next, I started a tiny command logging CPU usage every 3 seconds, to identify the processes responsible for the problem: while true; do date >> logfile.txt; ps -eo pcpu,pid,comm | sort -k 1 -r | head -10 >> logfile.txt; echo -e '\n-----------------------\n' >> logfile.txt; sleep 3; done

Do not use ps for this. Use top: top -b >> logfile.txt

When I came back to my desk and heard the laptop's fans running at full speed, I checked the logfile immiediately - it turned out, that... nothing actually eats the whole CPU. The most CPU-intensive application was indeed compiz, but it used 3.2% of the CPU at most. during the whole time, there was no indication of any process going mad. Here's a sample log frame:

 3.1  2732 compiz
 2.1  3510 chrome
 1.8  1141 Xorg
 1.4  3566 chrome
 1.4 24014 evolution
 0.9  3733 chrome
 0.9 21418 firefox
 0.8  3489 psensor
 0.4  4164 abiword
 0.3 20256 chrome

Do you have any idea what I could do next to fix the issue, or at least find the cause?

Solution 1:

I noticed some heat issues with Ubuntu as well, that is to say I really noticed the heat after picking up a very hot idle laptop.

Ultimately for me the solution was as simple as a can of well applied air duster to make sure the cooling system could function more efficiently.