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I tested CPU frequencies with either the Intel tool i7z and turbostat from the linux-tools package (sudo modprobe msr, sudo turbostat) and what I find as maximum frequencies for two different processors is lower as what Intel states as maximum turbo frequency.

I tested with MrBayes MPI on 4 cores with governors ondemand and performance and the 'turbo' option using indicator-cpufreq.

  1. i5-3210M - Intel specifications max. freq.: 2,5GHz - 3,1GHz Turbo

    max. measured: 2,89GHz

  2. i5-3470 - Intel specifications: 3,2GHz - 3,6GHz Turbo

    max. measured:3,39GHz

I also tried for i in {1..4}; do burnK7 & done in tty1 and turbostat in tty2 and got the same results.

Why are the max. Turbo CPU frequency I can measure running Ubuntu lower than the ones Intel states? Where are the "missing" 0,21GHz?

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Are you in a situation where turbo is needed? Something like burnK7. It's old but should stress out a single core and cause it to enter turbo. –  Oli Jun 7 '13 at 9:39
    
Possible duplicated: askubuntu.com/questions/37618/is-turbo-boost-working –  Leo Jun 7 '13 at 9:43
    
This is not a question doubting Turbo Boost in general but asking why Turbo Boost is not running at maximum possible speed. –  joschi Jun 7 '13 at 9:50
    
Added test information to the question. –  joschi Jun 7 '13 at 9:50
    
You can try to start the tty1, do a sudo service lightdm stop to stop graphical processes that would be running in the CPU and run this while :; do :; done while in tty2 you execute the sudo turbostat or i7z monitors. –  Leo Jun 7 '13 at 13:13

2 Answers 2

up vote 3 down vote accepted

Actually as you are running all 4 cores, the maximum frequency won't be achieved as specified. Intel specifies maximum turbo frequency for a single running core.

There are different maximum frequencies achieved for 1 active core and for 4 active cores (to prevent going over TDP) http://www.cpu-world.com/CPUs/Core_i5/Intel-Core%20i5-3210M%20(BGA)%20Mobile%20processor.html

e.g. thus you are getting around 2.9 ghz rather than 3.1

if you look in i7z there is a line specifying //// max multiplier achieved with 1/2/3/4 core. You cannot go above those multipliers if more than some number of cores are active.

also, inactive core need to be in C3 or higher states to allow the active core(s) to get into higher turbo levels.

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Didn't knwo that there was a difference in max. Turbo core frequencies when more than one is used. Thanks for the information. –  joschi Jun 8 '13 at 11:19

Your BIOS sets these values so you will have to check with your motherboard vendor. In my case, I can configure it to whatever I want since I have a motherboard meant for overclocking and an unlocked CPU.

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I only have a switch for enable/disable Turbo Boost in the BIOS. And it's enabled, of course. –  joschi Jun 7 '13 at 14:46

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