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CPU usage at 100% for several hours
Is it ok to have 100% CPU usage constantly

I wonder which case is more harmful: high percentage of usage (>90%) vs high temperature (> 70 or 80 celcius degree), both for several hours?

I only know high temperature is bad, but I am not sure about high percentage of CPU usage.

If one can choose between "higher usage and lower temperature" vs "lower usage and higher temperature", by for example scaling CPU frequency and using command cpulimit in Ubuntu, what is the recommendation for choice?

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High percentage of CPU usage should not be harmful, since CPUs does not have any moving parts, that degrade after some amount of usage.

Theoretically it could, but I've yet to see a failed CPU because of high usage. (You can even safely use them 24/7/365.)

Heat is another problem which will reduce CPU life. (Another one is overclocking.) It correlates with usage and the more heat is produced, the shorter the lifetime.

But again, appropriate cooling that keeps temperatures in the „middle region” of the specification range will enable continuous usage.

In my opinion it boils down to this: if you can keep the temperature low, the percentage of the usage does not matter.

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  • Thanks! (1) How do I know if I am overclocking? I have several options for CPU frequencies from low to high, but I don't know if the high one is overclock or not. (2) What is the middle region for CPU temperature?
    – Tim
    Commented Jun 4, 2012 at 11:30
  • You should know the exact CPU model you have in your machine. Every manufacturer publishes a specification page for your processor that contains this information. (eg. ark.intel.com) Usually Tcase specifies the maximum case temperature. As for the overclocking, you can compare the resulting CPU frequency with that on the box.
    – lgarzo
    Commented Jun 4, 2012 at 11:42
  • My CPU is Intel® Core™2 Duo CPU P8800 @ 2.66GHz × 2. (1) cpufreq on Ubuntu only provides up to 2.67 GHz to scale to, so I wonder how overclocking can be done? (2) I cannot find my CPU at ark.intel.com/products/family/26547/…. Also there is no temperature range for each CPU there. So I wonder how to find it?
    – Tim
    Commented Jun 4, 2012 at 11:58
  • 1) You do not seem to overclock your CPU, it is usually done in your BIOS. 2) This is your product page: ark.intel.com/products/40380/… 2.b) In this case the Tjunction is specified, find details about it eg. here: techpowerup.com/forums/showthread.php?t=45840
    – lgarzo
    Commented Jun 4, 2012 at 12:34
  • Thanks! About temperature: (1) What does Tjunction mean? Is a part of CPU or close to CPU? (2) I use Psensor to monitor temperatures, but it gives so many items, from temp1, temp2, fan1, temp1, temp2, ..., temp11. I wonder which one is for Tjunction? (3) What is the recommended working temperature range for CPU to last long?
    – Tim
    Commented Jun 4, 2012 at 12:43
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If one can choose between "higher usage and lower temperature" vs "lower usage and higher temperature", by for example scaling CPU frequency and using command cpulimit in Ubuntu, what is the recommendation for choice?

You can't. Higher usage means higher temperature. Lower usage means lower temperature.

  • Underclocking your CPU frequency with cpufreq will only affect the percentage of CPU usage without lowering the temperature.

    The percentage is an absolutely meaningless value. With the exact same workload, your percentage might go up or down when under- or overclocking your CPU. But it's still the same workload, so any potential harm (and I'm not sure there is any) caused by usage will be exactly the same.

  • Likewise, cpulimit limits the CPU usage, thus keeping percentage and temperature low.

I only know high temperature is bad, but I am not sure about high percentage of CPU usage.

How hot is bad depends on each individual CPU. Your specific CPU will automatically shut down at 105ºC to prevent damage (source).

Nevertheless, 80ºC is a little hot. Even at 100% load, you should be able to stay below that temperature with appropriate cooling.

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  • thanks! (1) My experiences tell me that reducing frequency does lower temperature. Limiting cpu usage, while increasing frequency, will achieve lower usage and higher temperature. (2) What is the recommended working temperature range for CPU to last long?
    – Tim
    Commented Jun 4, 2012 at 12:49
  • (3) After fresh start of Ubuntu 12.04, my CPU temp is around 45~50 celcius degree. Is that normally cool or hot?
    – Tim
    Commented Jun 4, 2012 at 12:57
  • (1) You're talking about percentages, not actual usage. (2) I can't find the exact values for your CPU, but the lower the better. As a rule of thumb, you should not pass 50ºC when idle, 70ºC under load. (3) Still OK.
    – Dennis
    Commented Jun 4, 2012 at 13:00
  • About (1), percentage I said is the percentage of usage. For example, 100% usage at a low frequency and 50% usage at a doubled frequence, which one has more usage? How is the usage calculuated?
    – Tim
    Commented Jun 4, 2012 at 13:06
  • As I said in my answer, the percentage of usage is irrelevant. IF you have $5,- in your pocket and you spend $5,- of it on ice cream, you spent 100% of your money. If you had had $10,- in your pocket, you would have spent only 50% of it. But that doesn't make the ice cream any cheaper.
    – Dennis
    Commented Jun 4, 2012 at 13:12
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If we look at this question from an abstract point of view, then strickly speaking high temperature is more harmful, because CPUs do have temperature limits, but they don't have utilization limits. As far as the manufacturer is concerned they are made to be used 100% 24h/day. There is no spec specifying how long they will last at continuous 100% usage, but there is a max temperature spec.

Note: It's not really possible to answer this question properly if you don't specify values for "high load" and "high temperature", so I have to keep the answer in the abstract realm.

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