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Beginner
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RAPL - Per Core Power Measurement / Capping

Hi,

I'm trying to use RAPL to measure and powercap individual cores.
However, it seems that my experiments only achieve measurement / capping of all cores.

I have tried two ways to control the power on a per-core basis. My first attempt was to use the sysfs interface at "/sys/class/powercap/intel-rapl". Unfortunately, it only distinguishes between core ("intel-rapl:0:0"), uncore ("intel-rapl:0:1") and dram ("intel-rapl:0:2") for each package and does not subdivide into separate cores.
My second attempt was then to manually write a proper value into the MSR of each core ("/dev/cpu/$core/msr"), but this doesn't seem to work either.

I'm working with an Intel Xeon CPU E3-1275 v5 (Skylake, Family 6, Model 94).
Is there any way to measure and / or powercap individual cores with RAPL?

Thank you!

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Beginner
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Hi Dave,

When I followed your first approach and tried to cap the power by edit /sys/devices/virtual/powercap/intel-rapl/intel-rapl:0/constraint_0_power_limit_uw, the error message showed up: "constraint_1_power_limit_uw" E667: Fsync failed" even by using the root privilege. Do you have any ideas how to capping for all cores?

Thanks,

Kevin

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Beginner
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Kevin - Are you able to read the sysfs files, in the first place? I suspect there might be a BIOS/Kernel lock.

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Beginner
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Hello Srujan S, can you guide me how to unlock the RAPL limits? In my system, the BIOS has locked the RAPL package and DRAM limits. I can change the PP0 and PP1 limits but not Pkg and DRAM. I am using a Haswell m/c with Ubuntu 14.04 OS. Any help will be highly appreciated. than you.

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New Contributor I
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Anmol Panda wrote:

Hello Srujan S, can you guide me how to unlock the RAPL limits? In my system, the BIOS has locked the RAPL package and DRAM limits. I can change the PP0 and PP1 limits but not Pkg and DRAM. I am using a Haswell m/c with Ubuntu 14.04 OS. Any help will be highly appreciated. than you.

I had a similar problem with one of the machines. If the 63-bit of the RAPL_PKG_POWER_LIMIT has been set at boot by the BIOS, you cannot change it thereafter. I was told the only solution is to update to a BIOS version that has the 63-bit disabled.

Hope this helps.

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Highlighted
New Contributor I
52 Views

Anmol Panda wrote:

Hello Srujan S, can you guide me how to unlock the RAPL limits? In my system, the BIOS has locked the RAPL package and DRAM limits. I can change the PP0 and PP1 limits but not Pkg and DRAM. I am using a Haswell m/c with Ubuntu 14.04 OS. Any help will be highly appreciated. than you.

I had a similar problem with one of the machines. If the 63-bit of the RAPL_PKG_POWER_LIMIT has been set at boot by the BIOS, you cannot change it thereafter. I was told the only solution is to update to a BIOS version that has the 63-bit disabled.

Hope this helps.

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