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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
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Are you looking for the internal implementation?
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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,
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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
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@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
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Thank you all,
Mustafa

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