`On Tuesday 02 Oct 2018 at 14:25:35 (+0200), Peter Zijlstra wrote:> On Wed, Sep 12, 2018 at 10:12:58AM +0100, Quentin Perret wrote:> > +/**> > + * em_pd_energy() - Estimates the energy consumed by the CPUs of a perf. domain> > + * @pd		: performance domain for which energy has to be estimated> > + * @max_util	: highest utilization among CPUs of the domain> > + * @sum_util	: sum of the utilization of all CPUs in the domain> > + *> > + * Return: the sum of the energy consumed by the CPUs of the domain assuming> > + * a capacity state satisfying the max utilization of the domain.> > + */> > +static inline unsigned long em_pd_energy(struct em_perf_domain *pd,> > +				unsigned long max_util, unsigned long sum_util)> > +{> > +	unsigned long freq, scale_cpu;> > +	struct em_cap_state *cs;> > +	int i, cpu;> > +> > +	/*> > +	 * In order to predict the capacity state, map the utilization of the> > +	 * most utilized CPU of the performance domain to a requested frequency,> > +	 * like schedutil.> > +	 */> > +	cpu = cpumask_first(to_cpumask(pd->cpus));> > +	scale_cpu = arch_scale_cpu_capacity(NULL, cpu);> > +	cs = &pd->table[pd->nr_cap_states - 1];> > +	freq = map_util_freq(max_util, cs->frequency, scale_cpu);> > +> > +	/*> > +	 * Find the lowest capacity state of the Energy Model above the> > +	 * requested frequency.> > +	 */> > +	for (i = 0; i < pd->nr_cap_states; i++) {> > +		cs = &pd->table[i];> > +		if (cs->frequency >= freq)> > +			break;> > +	}> > +> > +	/*> > +	 * The capacity of a CPU in the domain at that capacity state (cs)> > +	 * can be computed as:> > +	 *> > +	 *             cs->freq * scale_cpu> > +	 *   cs->cap = --------------------                          (1)> > +	 *                 cpu_max_freq> > +	 *> > +	 * So, the energy consumed by this CPU at that capacity state is:> > +	 *> > +	 *             cs->power * cpu_util> > +	 *   cpu_nrg = --------------------                          (2)> > +	 *                   cs->cap> > +	 *> > +	 * since 'cpu_util / cs->cap' represents its percentage of busy time.> > +	 *> > +	 *   NOTE: Although the result of this computation actually is in> > +	 *         units of power, it can be manipulated as an energy value> > +	 *         over a scheduling period, since it is assumed to be> > +	 *         constant during that interval.> > +	 *> > +	 * By injecting (1) in (2), 'cpu_nrg' can be re-expressed as a product> > +	 * of two terms:> > +	 *> > +	 *             cs->power * cpu_max_freq   cpu_util> > +	 *   cpu_nrg = ------------------------ * ---------          (3)> > +	 *                    cs->freq            scale_cpu> > +	 *> > +	 * The first term is static, and is stored in the em_cap_state struct> > +	 * as 'cs->cost'.> > +	 *> > +	 * Since all CPUs of the domain have the same micro-architecture, they> > +	 * share the same 'cs->cost', and the same CPU capacity. Hence, the> > +	 * total energy of the domain (which is the simple sum of the energy of> > +	 * all of its CPUs) can be factorized as:> > +	 *> > +	 *            cs->cost * \Sum cpu_util> > +	 *   pd_nrg = ------------------------                       (4)> > +	 *                  scale_cpu> > +	 */> > +	return cs->cost * sum_util / scale_cpu;> > +}> > Should we explicitly mention that this ignores idle costs?More doc shouldn't hurt so I can add a little something if you feel it'sneeded.Thanks,Quentin`