Need some information of Core i7, Shutting down cores in Linux and C states

idata — Sat, 05 Dec 2009 10:35:24 GMT

I am doing some experiments with the i7 and Linux 2.6.30. This question has to with Core i7 and linux.

I enable the C6 state in the bios and have a wattmeter that says that the wattage at idle is around 186 watts when all cores are Active. I can independently see them being much of the time in C6 state via a software.

I shut down the cores using echo "0" > /sys/devices/system/cpu/cpuX/online where X is the core i want to shut down.

But then the wattage shoots upto 196 Watts, which i am inferring implies that the shut down core now goes into a C1 sleep state rather than C6 state. Is this a problem with linux or with the processor?

A related problem: Why does some USB devices prevent i7 processor to get into C6 states? I have a wattsup-pro device and whenever i start reading data from it, the processor mysteriously only runs in C0-C1 state, but usually when the reading is off it runs nicely in C6 state.

I want to zero onto the reason why this happen. I couldn't find any i7 dedicated developer forums so i am posting it here. Any information or direction to someone who knows this will be most appreciated.

Thanks for reading.

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Need some information of Core i7, Shutting down cores in Linux and C states