On Tue, Mar 08, 2016 at 07:00:57PM +0100, Rafael J. Wysocki wrote: > On Tue, Mar 8, 2016 at 12:27 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > Seeing how frequency invariance is an arch feature, and cpufreq drivers > > are also typically arch specific, do we really need a flag at this > > level? > > The next frequency is selected by the governor and that's why. The > driver gets a frequency to set only. > > Now, the governor needs to work with different platforms, so it needs > to know how to deal with the given one. Ah, indeed. In any case, the availability of arch_sched_scale_freq() is a compile time thingy, so we can, at compile time, know what to use. > > In any case, I think the only difference between the two formula should > > be the addition of (1) for the platforms that do not already implement > > frequency invariance. > > OK > > So I'm reading this as a statement that linear is a better > approximation for frequency invariant utilization. Well, (1) is what the scheduler does with frequency invariance, except that allows a more flexible definition of 'current frequency' by asking for it every time we update the util stats. But if a platform doesn't need this, ie. it has a fixed frequency, or simply doesn't provide anything like this, assuming we run at the frequency we asked for is a reasonable assumption no? > This means that on platforms where the utilization is frequency > invariant we should use > > next_freq = a * x > > (where x is given by (2) above) and for platforms where the > utilization is not frequency invariant > > next_freq = a * x * current_freq / max_freq > > and all boils down to finding a. Right. > Now, it seems reasonable for a to be something like (1 + 1/n) * > max_freq, so for non-frequency invariant we get > > nex_freq = (1 + 1/n) * current_freq * x This seems like a big leap; where does: (1 + 1/n) * max_freq come from? And what is 'n'? -- 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
