 Messages in this thread Date Tue, 2 Oct 2018 14:25:35 +0200 From Peter Zijlstra <> Subject Re: [PATCH v7 03/14] PM: Introduce an Energy Model management framework
`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?`   Last update: 2018-10-02 14:27    [W:0.113 / U:1.076 seconds]
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