From what I understand Intel Turbo Boost "accelerates processor [...], automatically allowing processor cores to run faster than the rated operating frequency if they’re operating below power, current, and temperature specification limits." (Source: Intel)

BUT there is multiple things I don't get:

My cpu is a Intel Xeon E5-1660 v4 @ 3.20GHz. Which mean 3.20GHz is my max clock speed. Which I have on every cores if I disable Turbo Boost either in the BIOS or by using sh$wrmsr -p0 0x1a0 0x4000850089 at runtime.

IF I enable Turbo Boost, ALL of the 8 cores will be constant at 3.40GHz even when not stressed. Which is over the 3.20GHz limit.

AND HERE is the first thing I don't understand: When I look at temperature all cores are around 45 C However here (The thermal guide of this cpu) page 25 it says that my TDP should be around 95 C. So why Turbo boost doesn't boost over 3.40GHz, maybe because of power/current limit but how can I check that?

The other thing I don't understand is: When I disable all cores but 2 in the BIOS the Hz of the two last cores on are at 3.8Ghz and 3.6Ghz (3.8Ghz is the max clock I should get with Turbo Boost if you believe what it is said here). BUT when I enable every cores in the BIOS and disable it at runtime with sh$echo 0 > /sys/devices/system/cpu/cpuX/online (with X=2->7) the Hz of the two last cores are still 3.4GHz and doesn't change... So my guess is the way I disable at run time is not acknowledge by Turbo Boost. Why ?

To check my clock speed I use: sh$watch -n 1 "cat /proc/cpuinfo |grep \"cpu MHz\""

To check my cpu temperature I use: sh$watch -n 1 sensors

Others things related: Cpu driver is pstate and the governors for every cpu is performance. And when I monitor the clock speed or cpu temperature I do not forget to stress the cpu.

PS: The title might be not really appropriate... But i can't find a better one...


As far as I am aware, as you increase the number of cores being boosted, the max frequency drops, to account for the increased heat running more than one core creates. So while 1 core will happily run at 3.8ghz, Turbo Boost won't allow all cores to run at this speed.

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