> ... we probably never want to even try > to solve it in the scheduler, because why the hell should we care and add > complex logic for something like that? Today we take cores down to 100% idle, one at a time. This is useful, but isn't the best we can do. For we get zero "uncore" power savings. As long as at least one core is active anywhere in the system, all the uncores in all the packages in the system must remain active. What a scheduler-based solution could do is instead of taking, say, 1 of 64 cores down for 100% of the period, it could take all 64 cores down for 64th of the same period. This could get the hardware into the deeper "package C-states", for a measurable net power savings. At the same time, this system-wide throttling may mitigate some of the fairness/availability issues raised regarding taking cores 100% off-line. But doing this optimally will not be trivial. The hardware must stay in the deep-sleep-states long enough to make it worth the energy to enter and exit those states. The hardware will flush the caches, having a performance impact on all the cores. Device interrupts would prevent the cores from sleeping, so they'd need to be somehow delayed if we are to sleep long enough to make sleeping worth it etc. cheers, -Len Brown, Intel Open Source Technology Center -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
