From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>,
        Juri Lelli <juri.lelli@arm.com>, mturquette <mturquette@baylibre.com>,
        Linux PM list <linux-pm@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Steve Muckle <steve.muckle@linaro.org>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>
Subject: Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler utilization data
Date: Thu, 10 Mar 2016 23:28:29 +0100
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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.GB6375@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.