On Thursday, March 10, 2016 11:56:14 AM Peter Zijlstra wrote: > On Thu, Mar 10, 2016 at 11:30:08AM +0100, Peter Zijlstra wrote: > > On Thu, Mar 10, 2016 at 05:23:54PM +0700, Vincent Guittot wrote: > > > > > > No, since its a compile time thing, we can simply do: > > > > > > > > #ifdef arch_scale_freq_capacity > > > > next_freq = (1 + 1/n) * max_freq * (util / max) > > > > #else > > > > next_freq = (1 + 1/n) * current_freq * (util_raw / max) > > > > #endif > > > > > > selecting formula at compilation is clearly better. I wrongly thought that > > > it can't be accepted as a solution. > > > > Well, its bound to get more 'interesting' since I forse implementations > > not always actually doing the invariant thing. > > > > Take for example the thing I send: > > > > lkml.kernel.org/r/20160303162829.gb6...@twins.programming.kicks-ass.net > > > > it both shows why you cannot talk about current_freq but also that the > > above needs a little more help (for the !X86_FEATURE_APERFMPERF case). > > > > But the !arch_scale_freq_capacity case should indeed be that simple. > > Maybe something like: > > #ifdef arch_scale_freq_capacity > #ifndef arch_scale_freq_invariant > #define arch_scale_freq_invariant() (true) > #endif > #else /* arch_scale_freq_capacity */ > #define arch_scale_freq_invariant() (false) > #endif > > if (arch_scale_freq_invariant()) > > And have archs that have conditional arch_scale_freq_capacity() > implementation provide a arch_scale_freq_invariant implementation.
Yeah, looks workable to me.
