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I'm looking at Resmon on Windows 8 Basic. I have chosed the "high performance" power plan, which I thought would keep my CPU at the highest levels possible.

When the machine is (mostly) idle, the CPU Frequency is at 95%+, and the CPU usage is under 10%.

When I put the system under heavy load, the CPU frequency starts jumping around between 10% and 110%. The CPU usage jumps around as an inverse of the CPU frequency (which makes sense).

Why would my CPU frequence DECREASE when the system is under load? Is this some kind of thermal management issue (the CPU is getting hot, so the system slows the CPU to allow heat to dissipate)?

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UPDATE: I will try to post a screenshot later (security policies getting in the way of me doing my job...). HWMonitor is reporting CPU temps in the 60-70 C range. Max is no higher than 70C.

UPDATE-2: The CPU is an i7-3770, according to HWMonitor

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migrated from serverfault.com Aug 20 '13 at 15:17

This question came from our site for professional system and network administrators.

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Try a program such as hwmonitor or speedfan to monitor the CPU temperature. if it goes beyond 80-100°C, that would be the potential cause. Although i had the problem on my laptop once, a failing battery made the CPU run at 33% sometimes and it was unable to go back to 100% without unplugging the battery and rebooting. –  Kwaio Aug 20 '13 at 15:22
    
Can you post a screenshot of the Resmon window? Also, can you state what model of CPU you have? –  Craig Watson Aug 20 '13 at 15:36
    
Your CPU as it heats up will decide if it can run at a higher frequency or not. You won't be able to prevent you CPU from doing this. –  Ramhound Aug 20 '13 at 15:47

1 Answer 1

This is due to the Intel Turbo Boost Technology. This enables the processor to disable/enable processor cores and change the frequency of the cores.

This technology enables to choose how to distribute the maximum thermal limit. So if the processor has only 1 core activated, you can get up to 3.9 GHz. But when there are all 4 cores activated you get only up to 3.4 GHz per core. The technology now chooses the best option for the current applications running.

So you said you were putting your system under heavy load, well here we need to distinguish between single-threaded and multi-threaded load:

  • Single-thread load (i.e. Gaming): Cores are disabled and all power given to one core and the frequency can be increased to improve the performance for the single thread.
  • Multi-Thread enabled load: More cores activated (parallel processing), but lower frequency per core.

So I think your system has in the idle situation not all cores activated and enables a higher possible frequency. Then your load is multi-threaded and the core frequency is lower but the whole processor is under load.

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