Intel RAPL's effect on individual cores

[Mustafa_K_]

Hello,

What I understand you can set power limit to whole package using RAPL. Is there any explanation how this is achieved? Each core is assigned to same p-state ? Is there a description out there?

Thank you

[Bernard]

Are you looking for the internal implementation?

[Mustafa_K_]

Not necessarily the internal implementation but I couldn't find how each core contributes to overall power consumption of the package. So what I am looking is an algorithm or scheme that explains how each core's power limit is determined to achieve overall power consumption limit.

Thank you,

[Patrick_F_Intel1]

Hello Mustafa,

The Intel SDM vol 3 talks around this topic. See http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-system-programming-manual-325384.pdf section 14 for the RAPL (Running Average Power Limit) interface and MSRs. All the cores are 1 power plane and the GT graphics unit is on another power plane. You can limit the power used by the cores and the GPU.  And you can set a preference for which has priority when both the CPU & GPU want to run. From a crude test I ran trying to load up the CPU & GPU, the CPU gets the frequency reduced to stay within the overall package thermal limits.

There is a nice presentation at hotchips.org on Haswell which talks about power management. See http://www.hotchips.org/wp-content/uploads/hc_archives/hc25/HC25.80-Processors2-epub/HC25.27.820-Haswell-Hammarlund-Intel.pdf.

From the above presentation, it looks like haswell can set independent voltages for each core (and probably independent frequencies for each core). And the ring/LLC has its own voltage and the GPU has its own voltage. So there are many variables which can impact power usage.

Pat

[Bernard]

@Mustafa

Please read also this paper about the power management of Sandy Bridge : http://www.hotchips.org/wp-content/uploads/hc_archives/hc23/HC23.19.9-Desktop-CPUs/HC23.19.921.SandyBridge_Power_10-Rotem-Intel.pdf

[Mustafa_K_]

Thank you all,

Mustafa