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I had been using Arch Linux 64 bit on a Gateway P6860FX for about two years, and recently switched to Ubuntu (also 64 bit). When I type on the keyboard, my left hand feels a lot more warmth than before, and the air coming out of the exhaust port is definitely hotter. (Odd, right now there's no extra heat at all...but anyway...) Only minutes ago did I discover there are ways to monitor the CPU temperature. I have no idea what it was for Arch, but on Ubuntu it's 60-something, rising to 88 when I run heavy number-crunching software for a few minutes.

There are good Q&As on this and Superuser on cleaning out dust, and ways to help the computer stay cool.

My question is: why would one linix distro run hotter than another? Is there some daemon running in one and not the other, or some device driver difference, or perhaps one but not the other sets the "run really hot" bit in the CPU's mode register, or what?

Can knowing this answer help me select the next distro to try? Given several candidate distros that are both 64 bit and meet various requirements, can we predict which ones are going to make this machine run hot?

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What does cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor show you on each system? –  Keith Mar 10 '11 at 7:53
    
A likely reason is that one but not the other sets the "run really hot" bit in the CPU's mode register. Or rather, the other instructs the CPU to slow down when it's not doing much. There are multiple methods for this, one of which is the CPU frequency scaling governor whose setting Keith suggests. –  Gilles Mar 10 '11 at 21:01
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3 Answers

up vote 6 down vote accepted

As geekosaur and Tshepang are saying: Assuming that both distributions are using the same kernel, remaining differences should boil down to default configuration settings.

It could be worth exploring a bit before switching distributions (changing settings is presumably quicker than installing a new OS), I suggest

  • Check System > Preferences > Appearance > Visual Effects - you may prefer "none" to put less load on the CPU and graphics.
  • Install and run PowerTOP, a Linux utility to help track down power consumption offenders. (It's available from the Ubuntu software center.)
  • There are a whole bunch of other settings that may affect power consumption, but PowerTOP will probably guide you to the ones that are most relevant.
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My visual effects are already off, as I prefer to hoard CPU and memory for science and image processing. Powertop looks interesting - it might help. –  DarenW Mar 10 '11 at 6:50
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Ubuntu also defaults to CPU-hungry eye candy (animated cursors and the like).

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and CPU-hungry == heat .... –  Johan Mar 10 '11 at 10:23
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Assuming that both are using the same upstream kernel, start by checking the differences between kernel configs for each. In Debian (and I suppose Ubuntu), this will be found in "/boot/config-2.6.32-5-686-bigmem". I would expect that a younger kernel is more likely to run cooler (latest and greatest mantra).

Are they both running a similar selection of packages? Note that Ubuntu will by default install a heck of a lot more stuff, and some of these would be long-running applications (e.g. daemons), which may ask more of the CPU attention than normal applications. Arch leans more on minimalism.

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Regarding packages: On the Arch system, I had a zillion manually compiled programs, huge science apps, while this fairly fresh Ubuntu setup has maybe 1/4 the stuff (so far). Nothing is stuff that would run all the time behind the scenes, besides normal networking, X11 etc. (AFIK!) –  DarenW Mar 10 '11 at 6:05
    
I see no /etc/*big* never mind that exact file name. Ubuntu changes many of the things in /etc relative to debian. –  DarenW Mar 10 '11 at 6:07
    
@dar I meant /boot/config.... –  Tshepang Mar 10 '11 at 6:33
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