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![Lukasz Luba](/assets/img/avatar_default.png)
The milli-Watts precision causes rounding errors while calculating efficiency cost for each OPP. This is especially visible in the 'simple' Energy Model (EM), where the power for each OPP is provided from OPP framework. This can cause some OPPs to be marked inefficient, while using micro-Watts precision that might not happen. Update all EM users which access 'power' field and assume the value is in milli-Watts. Solve also an issue with potential overflow in calculation of energy estimation on 32bit machine. It's needed now since the power value (thus the 'cost' as well) are higher. Example calculation which shows the rounding error and impact: power = 'dyn-power-coeff' * volt_mV * volt_mV * freq_MHz power_a_uW = (100 * 600mW * 600mW * 500MHz) / 10^6 = 18000 power_a_mW = (100 * 600mW * 600mW * 500MHz) / 10^9 = 18 power_b_uW = (100 * 605mW * 605mW * 600MHz) / 10^6 = 21961 power_b_mW = (100 * 605mW * 605mW * 600MHz) / 10^9 = 21 max_freq = 2000MHz cost_a_mW = 18 * 2000MHz/500MHz = 72 cost_a_uW = 18000 * 2000MHz/500MHz = 72000 cost_b_mW = 21 * 2000MHz/600MHz = 70 // <- artificially better cost_b_uW = 21961 * 2000MHz/600MHz = 73203 The 'cost_b_mW' (which is based on old milli-Watts) is misleadingly better that the 'cost_b_uW' (this patch uses micro-Watts) and such would have impact on the 'inefficient OPPs' information in the Cpufreq framework. This patch set removes the rounding issue. Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
349 lines
12 KiB
C
349 lines
12 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_ENERGY_MODEL_H
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#define _LINUX_ENERGY_MODEL_H
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#include <linux/cpumask.h>
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#include <linux/device.h>
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#include <linux/jump_label.h>
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#include <linux/kobject.h>
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#include <linux/rcupdate.h>
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#include <linux/sched/cpufreq.h>
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#include <linux/sched/topology.h>
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#include <linux/types.h>
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/**
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* struct em_perf_state - Performance state of a performance domain
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* @frequency: The frequency in KHz, for consistency with CPUFreq
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* @power: The power consumed at this level (by 1 CPU or by a registered
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* device). It can be a total power: static and dynamic.
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* @cost: The cost coefficient associated with this level, used during
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* energy calculation. Equal to: power * max_frequency / frequency
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* @flags: see "em_perf_state flags" description below.
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*/
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struct em_perf_state {
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unsigned long frequency;
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unsigned long power;
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unsigned long cost;
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unsigned long flags;
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};
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/*
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* em_perf_state flags:
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*
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* EM_PERF_STATE_INEFFICIENT: The performance state is inefficient. There is
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* in this em_perf_domain, another performance state with a higher frequency
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* but a lower or equal power cost. Such inefficient states are ignored when
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* using em_pd_get_efficient_*() functions.
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*/
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#define EM_PERF_STATE_INEFFICIENT BIT(0)
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/**
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* struct em_perf_domain - Performance domain
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* @table: List of performance states, in ascending order
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* @nr_perf_states: Number of performance states
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* @flags: See "em_perf_domain flags"
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* @cpus: Cpumask covering the CPUs of the domain. It's here
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* for performance reasons to avoid potential cache
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* misses during energy calculations in the scheduler
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* and simplifies allocating/freeing that memory region.
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*
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* In case of CPU device, a "performance domain" represents a group of CPUs
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* whose performance is scaled together. All CPUs of a performance domain
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* must have the same micro-architecture. Performance domains often have
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* a 1-to-1 mapping with CPUFreq policies. In case of other devices the @cpus
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* field is unused.
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*/
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struct em_perf_domain {
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struct em_perf_state *table;
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int nr_perf_states;
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unsigned long flags;
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unsigned long cpus[];
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};
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/*
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* em_perf_domain flags:
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*
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* EM_PERF_DOMAIN_MICROWATTS: The power values are in micro-Watts or some
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* other scale.
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*
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* EM_PERF_DOMAIN_SKIP_INEFFICIENCIES: Skip inefficient states when estimating
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* energy consumption.
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*
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* EM_PERF_DOMAIN_ARTIFICIAL: The power values are artificial and might be
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* created by platform missing real power information
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*/
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#define EM_PERF_DOMAIN_MICROWATTS BIT(0)
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#define EM_PERF_DOMAIN_SKIP_INEFFICIENCIES BIT(1)
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#define EM_PERF_DOMAIN_ARTIFICIAL BIT(2)
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#define em_span_cpus(em) (to_cpumask((em)->cpus))
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#define em_is_artificial(em) ((em)->flags & EM_PERF_DOMAIN_ARTIFICIAL)
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#ifdef CONFIG_ENERGY_MODEL
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/*
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* The max power value in micro-Watts. The limit of 64 Watts is set as
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* a safety net to not overflow multiplications on 32bit platforms. The
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* 32bit value limit for total Perf Domain power implies a limit of
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* maximum CPUs in such domain to 64.
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*/
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#define EM_MAX_POWER (64000000) /* 64 Watts */
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/*
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* To avoid possible energy estimation overflow on 32bit machines add
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* limits to number of CPUs in the Perf. Domain.
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* We are safe on 64bit machine, thus some big number.
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*/
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#ifdef CONFIG_64BIT
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#define EM_MAX_NUM_CPUS 4096
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#else
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#define EM_MAX_NUM_CPUS 16
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#endif
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/*
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* To avoid an overflow on 32bit machines while calculating the energy
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* use a different order in the operation. First divide by the 'cpu_scale'
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* which would reduce big value stored in the 'cost' field, then multiply by
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* the 'sum_util'. This would allow to handle existing platforms, which have
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* e.g. power ~1.3 Watt at max freq, so the 'cost' value > 1mln micro-Watts.
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* In such scenario, where there are 4 CPUs in the Perf. Domain the 'sum_util'
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* could be 4096, then multiplication: 'cost' * 'sum_util' would overflow.
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* This reordering of operations has some limitations, we lose small
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* precision in the estimation (comparing to 64bit platform w/o reordering).
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*
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* We are safe on 64bit machine.
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*/
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#ifdef CONFIG_64BIT
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#define em_estimate_energy(cost, sum_util, scale_cpu) \
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(((cost) * (sum_util)) / (scale_cpu))
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#else
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#define em_estimate_energy(cost, sum_util, scale_cpu) \
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(((cost) / (scale_cpu)) * (sum_util))
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#endif
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struct em_data_callback {
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/**
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* active_power() - Provide power at the next performance state of
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* a device
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* @dev : Device for which we do this operation (can be a CPU)
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* @power : Active power at the performance state
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* (modified)
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* @freq : Frequency at the performance state in kHz
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* (modified)
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*
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* active_power() must find the lowest performance state of 'dev' above
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* 'freq' and update 'power' and 'freq' to the matching active power
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* and frequency.
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*
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* In case of CPUs, the power is the one of a single CPU in the domain,
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* expressed in micro-Watts or an abstract scale. It is expected to
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* fit in the [0, EM_MAX_POWER] range.
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*
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* Return 0 on success.
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*/
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int (*active_power)(struct device *dev, unsigned long *power,
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unsigned long *freq);
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/**
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* get_cost() - Provide the cost at the given performance state of
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* a device
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* @dev : Device for which we do this operation (can be a CPU)
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* @freq : Frequency at the performance state in kHz
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* @cost : The cost value for the performance state
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* (modified)
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*
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* In case of CPUs, the cost is the one of a single CPU in the domain.
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* It is expected to fit in the [0, EM_MAX_POWER] range due to internal
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* usage in EAS calculation.
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*
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* Return 0 on success, or appropriate error value in case of failure.
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*/
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int (*get_cost)(struct device *dev, unsigned long freq,
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unsigned long *cost);
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};
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#define EM_SET_ACTIVE_POWER_CB(em_cb, cb) ((em_cb).active_power = cb)
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#define EM_ADV_DATA_CB(_active_power_cb, _cost_cb) \
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{ .active_power = _active_power_cb, \
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.get_cost = _cost_cb }
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#define EM_DATA_CB(_active_power_cb) \
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EM_ADV_DATA_CB(_active_power_cb, NULL)
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struct em_perf_domain *em_cpu_get(int cpu);
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struct em_perf_domain *em_pd_get(struct device *dev);
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int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
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struct em_data_callback *cb, cpumask_t *span,
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bool microwatts);
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void em_dev_unregister_perf_domain(struct device *dev);
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/**
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* em_pd_get_efficient_state() - Get an efficient performance state from the EM
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* @pd : Performance domain for which we want an efficient frequency
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* @freq : Frequency to map with the EM
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*
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* It is called from the scheduler code quite frequently and as a consequence
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* doesn't implement any check.
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*
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* Return: An efficient performance state, high enough to meet @freq
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* requirement.
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*/
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static inline
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struct em_perf_state *em_pd_get_efficient_state(struct em_perf_domain *pd,
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unsigned long freq)
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{
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struct em_perf_state *ps;
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int i;
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for (i = 0; i < pd->nr_perf_states; i++) {
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ps = &pd->table[i];
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if (ps->frequency >= freq) {
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if (pd->flags & EM_PERF_DOMAIN_SKIP_INEFFICIENCIES &&
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ps->flags & EM_PERF_STATE_INEFFICIENT)
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continue;
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break;
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}
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}
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return ps;
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}
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/**
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* em_cpu_energy() - Estimates the energy consumed by the CPUs of a
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* performance domain
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* @pd : performance domain for which energy has to be estimated
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* @max_util : highest utilization among CPUs of the domain
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* @sum_util : sum of the utilization of all CPUs in the domain
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* @allowed_cpu_cap : maximum allowed CPU capacity for the @pd, which
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* might reflect reduced frequency (due to thermal)
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*
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* This function must be used only for CPU devices. There is no validation,
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* i.e. if the EM is a CPU type and has cpumask allocated. It is called from
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* the scheduler code quite frequently and that is why there is not checks.
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*
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* Return: the sum of the energy consumed by the CPUs of the domain assuming
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* a capacity state satisfying the max utilization of the domain.
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*/
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static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
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unsigned long max_util, unsigned long sum_util,
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unsigned long allowed_cpu_cap)
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{
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unsigned long freq, scale_cpu;
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struct em_perf_state *ps;
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int cpu;
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if (!sum_util)
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return 0;
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/*
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* In order to predict the performance state, map the utilization of
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* the most utilized CPU of the performance domain to a requested
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* frequency, like schedutil. Take also into account that the real
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* frequency might be set lower (due to thermal capping). Thus, clamp
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* max utilization to the allowed CPU capacity before calculating
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* effective frequency.
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*/
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cpu = cpumask_first(to_cpumask(pd->cpus));
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scale_cpu = arch_scale_cpu_capacity(cpu);
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ps = &pd->table[pd->nr_perf_states - 1];
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max_util = map_util_perf(max_util);
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max_util = min(max_util, allowed_cpu_cap);
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freq = map_util_freq(max_util, ps->frequency, scale_cpu);
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/*
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* Find the lowest performance state of the Energy Model above the
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* requested frequency.
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*/
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ps = em_pd_get_efficient_state(pd, freq);
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/*
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* The capacity of a CPU in the domain at the performance state (ps)
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* can be computed as:
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*
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* ps->freq * scale_cpu
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* ps->cap = -------------------- (1)
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* cpu_max_freq
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*
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* So, ignoring the costs of idle states (which are not available in
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* the EM), the energy consumed by this CPU at that performance state
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* is estimated as:
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*
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* ps->power * cpu_util
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* cpu_nrg = -------------------- (2)
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* ps->cap
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*
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* since 'cpu_util / ps->cap' represents its percentage of busy time.
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*
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* NOTE: Although the result of this computation actually is in
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* units of power, it can be manipulated as an energy value
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* over a scheduling period, since it is assumed to be
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* constant during that interval.
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*
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* By injecting (1) in (2), 'cpu_nrg' can be re-expressed as a product
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* of two terms:
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*
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* ps->power * cpu_max_freq cpu_util
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* cpu_nrg = ------------------------ * --------- (3)
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* ps->freq scale_cpu
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*
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* The first term is static, and is stored in the em_perf_state struct
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* as 'ps->cost'.
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*
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* Since all CPUs of the domain have the same micro-architecture, they
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* share the same 'ps->cost', and the same CPU capacity. Hence, the
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* total energy of the domain (which is the simple sum of the energy of
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* all of its CPUs) can be factorized as:
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*
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* ps->cost * \Sum cpu_util
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* pd_nrg = ------------------------ (4)
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* scale_cpu
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*/
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return em_estimate_energy(ps->cost, sum_util, scale_cpu);
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}
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/**
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* em_pd_nr_perf_states() - Get the number of performance states of a perf.
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* domain
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* @pd : performance domain for which this must be done
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*
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* Return: the number of performance states in the performance domain table
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*/
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static inline int em_pd_nr_perf_states(struct em_perf_domain *pd)
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{
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return pd->nr_perf_states;
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}
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#else
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struct em_data_callback {};
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#define EM_ADV_DATA_CB(_active_power_cb, _cost_cb) { }
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#define EM_DATA_CB(_active_power_cb) { }
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#define EM_SET_ACTIVE_POWER_CB(em_cb, cb) do { } while (0)
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static inline
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int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
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struct em_data_callback *cb, cpumask_t *span,
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bool microwatts)
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{
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return -EINVAL;
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}
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static inline void em_dev_unregister_perf_domain(struct device *dev)
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{
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}
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static inline struct em_perf_domain *em_cpu_get(int cpu)
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{
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return NULL;
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}
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static inline struct em_perf_domain *em_pd_get(struct device *dev)
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{
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return NULL;
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}
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static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
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unsigned long max_util, unsigned long sum_util,
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unsigned long allowed_cpu_cap)
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{
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return 0;
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}
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static inline int em_pd_nr_perf_states(struct em_perf_domain *pd)
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{
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return 0;
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}
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#endif
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#endif
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