On 12 Nov 2013, at 16:48, Arjan van de Ven <ar...@linux.intel.com> wrote: > On 11/11/2013 10:18 AM, Catalin Marinas wrote: >> The ordering is based on the actual C-state, so a simple way is to wake >> up the CPU in the shallowest C-state. With asymmetric configurations >> (big.LITTLE) we have different costs for the same C-state, so this would >> come in handy. > > btw I was considering something else; in practice CPUs will be in the deepest > state.. > ... at which point I was going to go with some other metrics of what is best > from a platform level
I agree, other metrics are needed. The problem is that we currently only have (relatively, guessed from the target residency) the cost of transition from a C-state to a P-state (for the latter, not sure which). But we don’t know what the power (saving) on that C-state is nor the one at a P-state (and vendors reluctant to provide such information). So the best the scheduler can do is optimise the wake-up cost and blindly assume that deeper C-state on a CPU is more efficient than lower P-states on two other CPUs (or the other way around). If we find a good use for such metrics in the scheduler, I think the vendors would be more open to providing at least some relative (rather than absolute) numbers. Catalin-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
