Ubuntu – Is the Intel Turbo Boost Mode not running at maximum speed

cpuintelturbo-boost

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?

Best Answer

  • 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.