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Recent enough Intel processor use the Intel rapl driver for energy management.

This driver makes use of two power limit, the short term power limit, that allows higher power for short term thanks to inertia and the long term power limit, the average power, the processor dissipates when operating at Base Frequency with all cores active, also known as TDP.

The TDP is a number of Watts fixed by Intel to help manufacturers to dimension the heat dissipation system properly. However, some manufacturer set a lower number as default to the CPU.

This means the CPU you buy in a note(net)book is sometimes designed to do more than what it really does.

In general usage, this is still better to respect this setting by the manufacturer, this may be more optimal for battery management and avoid overheat as their cooling system is not built for the full TDP.

But in some cases, you have power plugged in (I use a 90W power supply instead of the original 45W), and you have additional cooling capabilities that makes some room for the temperature. In my case, I have an i7-3667U with a TDP of 17W (not that difficult to add something to take this out), but manufacturer set the long term limit to 10W.

Under Windows, there is the possibility to use Intel XTU to set these power limits to the wanted values. The operation remains safe as the processor has thermal security, and start thermal throttling at 75°C (T_Junction = 105 °C). Depending on the condition (additional cooling provided, air temperature, ...) it is possible to increase the long term power limit to reach around 70°C on long run (to keep a margin before the thermal throttling) with a power around Intel's TDP of 17W. The improvement in term of frequency is generally around 31-37.5%. Which can be interesting for some of the long operations I often have. This setting however do not persist after a reboot to a Linux operating system (where I do most of my work).

I however wasn't able to find similar settings under Linux. There is the possibility to play on the P-States, but I didn't found the way to increase this small 10W limit (I monitor the power consumed by the CPU).

So my question is: how can I modify (increase) the power limit of the rapl?

  • I found power_gov, I'll experiment a bit and gives the result: software.intel.com/en-us/articles/intel-power-governor – Togh Aug 16 '16 at 21:35
  • This tool is supposed to allow doing what I want but doesn't seem to do it. I had first to replace the rapl.c and .h from software.intel.com/en-us/articles/intel-power-gadget-20 to have support with Ivy Bridge, than to put the -lm at the end of the lines in the Makefile to be able to compile correctly. After that, the tool needs root privilege to run. It however displays as if the limits where 17 and 21 W, whereas the same tool doesn't show consumed power over 10W (shows 9 in fact). – Togh Aug 17 '16 at 9:56

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