Re: [RFC PATCH v4 09/12] sched/fair: Introduce an energy estimation helper function

[Quentin Perret <quentin.perret@arm.com>]

On Monday 09 Jul 2018 at 14:01:38 (+0200), Peter Zijlstra wrote:
> On Fri, Jul 06, 2018 at 06:04:44PM +0100, Quentin Perret wrote:
> > 'max_util' is basically the util we use to request an OPP. 'sum_util' is
> > how long the CPUs will be running.
> 
> A indeed. But yes bit of a mess, but it wants doing I think.

OK, understood.

> Perhaps a little something like the below... The alternative is two
> separate but closely related functions, not sure which is better.
> 
> 
> enum schedutil_type {
> 	frequency_util,
> 	energy_util,
> };

Hmm, this should work ... Should we also try to avoid the code
duplication in scale_rt_capacity() ? This doesn't want dependencies on
schedutil I assume so a little bit of extra work is required.

What about moving schedutil_freq_util() to sched.h and give it a more
generic name (total_cpu_util() ?) with no dependencies on
CONFIG_CPU_FREQ_GOV_SCHEDUTIL ? Also, 'energy_util' would have to be
renamed I guess (busy_time_util ?).

Then scale_rt_capacity() can be turned into something like (totally
untested):

static unsigned long scale_rt_capacity(int cpu)
{
	unsigned long util = total_cpu_util(cpu, 0, busy_time_util);

	return arch_scale_cpu_capacity(NULL, cpu) - util;
}

Thoughts ?

Thanks,
Quentin