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- ====================
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- Energy Model of CPUs
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- ====================
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+ .. SPDX-License-Identifier: GPL-2.0
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+
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+ =======================
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+ Energy Model of devices
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+ =======================
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1. Overview
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-----------
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The Energy Model (EM) framework serves as an interface between drivers knowing
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- the power consumed by CPUs at various performance levels, and the kernel
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+ the power consumed by devices at various performance levels, and the kernel
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subsystems willing to use that information to make energy-aware decisions.
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- The source of the information about the power consumed by CPUs can vary greatly
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+ The source of the information about the power consumed by devices can vary greatly
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from one platform to another. These power costs can be estimated using
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devicetree data in some cases. In others, the firmware will know better.
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Alternatively, userspace might be best positioned. And so on. In order to avoid
@@ -25,7 +27,7 @@ framework, and interested clients reading the data from it::
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+---------------+ +-----------------+ +---------------+
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| Thermal (IPA) | | Scheduler (EAS) | | Other |
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+---------------+ +-----------------+ +---------------+
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- | | em_pd_energy() |
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+ | | em_cpu_energy() |
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| | em_cpu_get() |
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+---------+ | +---------+
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| | |
@@ -35,7 +37,7 @@ framework, and interested clients reading the data from it::
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| Framework |
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+---------------------+
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^ ^ ^
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- | | | em_register_perf_domain ()
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+ | | | em_dev_register_perf_domain ()
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+----------+ | +---------+
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| | |
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+---------------+ +---------------+ +--------------+
@@ -47,12 +49,12 @@ framework, and interested clients reading the data from it::
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| Device Tree | | Firmware | | ? |
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+--------------+ +---------------+ +--------------+
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- The EM framework manages power cost tables per 'performance domain' in the
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- system. A performance domain is a group of CPUs whose performance is scaled
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- together. Performance domains generally have a 1-to-1 mapping with CPUFreq
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- policies. All CPUs in a performance domain are required to have the same
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- micro-architecture. CPUs in different performance domains can have different
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- micro-architectures.
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+ In case of CPU devices the EM framework manages power cost tables per
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+ 'performance domain' in the system. A performance domain is a group of CPUs
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+ whose performance is scaled together. Performance domains generally have a
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+ 1-to-1 mapping with CPUFreq policies. All CPUs in a performance domain are
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+ required to have the same micro-architecture. CPUs in different performance
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+ domains can have different micro-architectures.
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2. Core APIs
@@ -70,28 +72,37 @@ CONFIG_ENERGY_MODEL must be enabled to use the EM framework.
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Drivers are expected to register performance domains into the EM framework by
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calling the following API::
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- int em_register_perf_domain(cpumask_t *span , unsigned int nr_states,
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- struct em_data_callback *cb);
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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 *cpus );
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- Drivers must specify the CPUs of the performance domains using the cpumask
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- argument, and provide a callback function returning <frequency, power> tuples
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- for each capacity state. The callback function provided by the driver is free
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+ Drivers must provide a callback function returning <frequency, power> tuples
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+ for each performance state. The callback function provided by the driver is free
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to fetch data from any relevant location (DT, firmware, ...), and by any mean
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- deemed necessary. See Section 3. for an example of driver implementing this
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+ deemed necessary. Only for CPU devices, drivers must specify the CPUs of the
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+ performance domains using cpumask. For other devices than CPUs the last
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+ argument must be set to NULL.
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+ See Section 3. for an example of driver implementing this
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callback, and kernel/power/energy_model.c for further documentation on this
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API.
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2.3 Accessing performance domains
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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+ There are two API functions which provide the access to the energy model:
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+ em_cpu_get() which takes CPU id as an argument and em_pd_get() with device
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+ pointer as an argument. It depends on the subsystem which interface it is
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+ going to use, but in case of CPU devices both functions return the same
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+ performance domain.
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+
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Subsystems interested in the energy model of a CPU can retrieve it using the
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em_cpu_get() API. The energy model tables are allocated once upon creation of
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the performance domains, and kept in memory untouched.
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The energy consumed by a performance domain can be estimated using the
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- em_pd_energy() API. The estimation is performed assuming that the schedutil
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- CPUfreq governor is in use.
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+ em_cpu_energy() API. The estimation is performed assuming that the schedutil
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+ CPUfreq governor is in use in case of CPU device. Currently this calculation is
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+ not provided for other type of devices.
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More details about the above APIs can be found in include/linux/energy_model.h.
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@@ -106,42 +117,46 @@ EM framework::
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-> drivers/cpufreq/foo_cpufreq.c
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- 01 static int est_power(unsigned long *mW, unsigned long *KHz, int cpu)
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- 02 {
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- 03 long freq, power;
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- 04
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- 05 /* Use the 'foo' protocol to ceil the frequency */
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- 06 freq = foo_get_freq_ceil(cpu, *KHz);
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- 07 if (freq < 0);
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- 08 return freq;
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- 09
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- 10 /* Estimate the power cost for the CPU at the relevant freq. */
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- 11 power = foo_estimate_power(cpu, freq);
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- 12 if (power < 0);
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- 13 return power;
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- 14
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- 15 /* Return the values to the EM framework */
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- 16 *mW = power;
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- 17 *KHz = freq;
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- 18
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- 19 return 0;
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- 20 }
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- 21
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- 22 static int foo_cpufreq_init(struct cpufreq_policy *policy)
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- 23 {
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- 24 struct em_data_callback em_cb = EM_DATA_CB(est_power);
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- 25 int nr_opp, ret;
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- 26
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- 27 /* Do the actual CPUFreq init work ... */
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- 28 ret = do_foo_cpufreq_init(policy);
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- 29 if (ret)
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- 30 return ret;
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- 31
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- 32 /* Find the number of OPPs for this policy */
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- 33 nr_opp = foo_get_nr_opp(policy);
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- 34
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- 35 /* And register the new performance domain */
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- 36 em_register_perf_domain(policy->cpus, nr_opp, &em_cb);
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- 37
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- 38 return 0;
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- 39 }
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+ 01 static int est_power(unsigned long *mW, unsigned long *KHz,
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+ 02 struct device *dev)
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+ 03 {
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+ 04 long freq, power;
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+ 05
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+ 06 /* Use the 'foo' protocol to ceil the frequency */
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+ 07 freq = foo_get_freq_ceil(dev, *KHz);
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+ 08 if (freq < 0);
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+ 09 return freq;
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+ 10
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+ 11 /* Estimate the power cost for the dev at the relevant freq. */
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+ 12 power = foo_estimate_power(dev, freq);
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+ 13 if (power < 0);
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+ 14 return power;
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+ 15
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+ 16 /* Return the values to the EM framework */
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+ 17 *mW = power;
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+ 18 *KHz = freq;
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+ 19
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+ 20 return 0;
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+ 21 }
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+ 22
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+ 23 static int foo_cpufreq_init(struct cpufreq_policy *policy)
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+ 24 {
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+ 25 struct em_data_callback em_cb = EM_DATA_CB(est_power);
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+ 26 struct device *cpu_dev;
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+ 27 int nr_opp, ret;
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+ 28
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+ 29 cpu_dev = get_cpu_device(cpumask_first(policy->cpus));
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+ 30
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+ 31 /* Do the actual CPUFreq init work ... */
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+ 32 ret = do_foo_cpufreq_init(policy);
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+ 33 if (ret)
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+ 34 return ret;
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+ 35
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+ 36 /* Find the number of OPPs for this policy */
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+ 37 nr_opp = foo_get_nr_opp(policy);
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+ 38
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+ 39 /* And register the new performance domain */
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+ 40 em_dev_register_perf_domain(cpu_dev, nr_opp, &em_cb, policy->cpus);
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+ 41
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+ 42 return 0;
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+ 43 }
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