On Fri, Jun 06, 2014 at 12:50:36PM +0200, Peter Zijlstra wrote: > > Voltage is combined with frequency, roughly, voltage is proportional > > to freuquecy, so roughly, power is proportionaly to voltage^3. You > > P ~ V^2, last time I checked. > > > can't say which is more important, or there is no reason to raise > > voltage without raising frequency. > > Well, some chips have far fewer voltage steps than freq steps; or, > differently put, they have multiple freq steps for a single voltage > level. > > And since the power (Watts) is proportional to Voltage squared, its the > biggest term. > > If you have a distinct voltage level for each freq, it all doesn't > matter. >
Ok. I think we understand each other. But one more thing, I said P ~ V^3, because P ~ V^2*f and f ~ V, so P ~ V^3. Maybe some frequencies share the same voltage, but you can still safely assume V changes with f in general, and it will be more and more so, since we do need finer control over power consumption. > Sure, but realize that we must fully understand this governor and > integrate it in the scheduler if we're to attain the goal of IPC/watt > optimized scheduling behaviour. > Attain the goal of IPC/watt optimized? I don't see how it can be done like this. As I said, what is unknown for prediction is perf scaling *and* changing workload. So the challenge for pstate control is in both. But I see more chanllenge in the changing workload than in the performance scaling or the resulting IPC impact (if workload is fixed). Currently, all freq governors take CPU utilization (load%) as the indicator (target), which can server both: workload and perf scaling. As for IPC/watt optimized, I don't see how it can be practical. Too micro to be used for the general well-being? > So you (or rather Intel in general) will have to be very explicit on how > their stuff works and can no longer hide in some driver and do magic. > The same is true for all other vendors for that matter. > > If you (vendors, not Yuyang in specific) do not want to play (and be > explicit and expose how your hardware functions) then you simply will > not get power efficient scheduling full stop. > > There's no rocks to hide under, no magic veils to hide behind. You tell > _in_public_ or you get nothing. Better communication is good, especially for our increasingly iterated products because the changing products do incur noises and inconsistency in detail. -- 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/
