| energy-model.rst (d704aa0d44ade12660d4d7220b2a8d785b7b4247) | energy-model.rst (08374410a5ea3ff2fa9a87edd7d7ab15375b1c31) |
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| 1.. SPDX-License-Identifier: GPL-2.0 2 3======================= 4Energy Model of devices 5======================= 6 71. Overview 8----------- --- 70 unchanged lines hidden (view full) --- 79^^^^^^^^^^^^^^^^^^ 80 81CONFIG_ENERGY_MODEL must be enabled to use the EM framework. 82 83 842.2 Registration of performance domains 85^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 86 | 1.. SPDX-License-Identifier: GPL-2.0 2 3======================= 4Energy Model of devices 5======================= 6 71. Overview 8----------- --- 70 unchanged lines hidden (view full) --- 79^^^^^^^^^^^^^^^^^^ 80 81CONFIG_ENERGY_MODEL must be enabled to use the EM framework. 82 83 842.2 Registration of performance domains 85^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 86 |
| 87Registration of 'advanced' EM 88~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 89 90The 'advanced' EM gets it's name due to the fact that the driver is allowed 91to provide more precised power model. It's not limited to some implemented math 92formula in the framework (like it's in 'simple' EM case). It can better reflect 93the real power measurements performed for each performance state. Thus, this 94registration method should be preferred in case considering EM static power 95(leakage) is important. 96 |
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| 87Drivers are expected to register performance domains into the EM framework by 88calling the following API:: 89 90 int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states, 91 struct em_data_callback *cb, cpumask_t *cpus, bool milliwatts); 92 93Drivers must provide a callback function returning <frequency, power> tuples 94for each performance state. The callback function provided by the driver is free 95to fetch data from any relevant location (DT, firmware, ...), and by any mean 96deemed necessary. Only for CPU devices, drivers must specify the CPUs of the 97performance domains using cpumask. For other devices than CPUs the last 98argument must be set to NULL. 99The last argument 'milliwatts' is important to set with correct value. Kernel 100subsystems which use EM might rely on this flag to check if all EM devices use 101the same scale. If there are different scales, these subsystems might decide 102to: return warning/error, stop working or panic. 103See Section 3. for an example of driver implementing this 104callback, or Section 2.4 for further documentation on this API 105 | 97Drivers are expected to register performance domains into the EM framework by 98calling the following API:: 99 100 int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states, 101 struct em_data_callback *cb, cpumask_t *cpus, bool milliwatts); 102 103Drivers must provide a callback function returning <frequency, power> tuples 104for each performance state. The callback function provided by the driver is free 105to fetch data from any relevant location (DT, firmware, ...), and by any mean 106deemed necessary. Only for CPU devices, drivers must specify the CPUs of the 107performance domains using cpumask. For other devices than CPUs the last 108argument must be set to NULL. 109The last argument 'milliwatts' is important to set with correct value. Kernel 110subsystems which use EM might rely on this flag to check if all EM devices use 111the same scale. If there are different scales, these subsystems might decide 112to: return warning/error, stop working or panic. 113See Section 3. for an example of driver implementing this 114callback, or Section 2.4 for further documentation on this API 115 |
| 116Registration of 'simple' EM 117~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
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| 106 | 118 |
| 119The 'simple' EM is registered using the framework helper function 120cpufreq_register_em_with_opp(). It implements a power model which is tight to 121math formula:: 122 123 Power = C * V^2 * f 124 125The EM which is registered using this method might not reflect correctly the 126physics of a real device, e.g. when static power (leakage) is important. 127 128 |
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| 1072.3 Accessing performance domains 108^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 109 110There are two API functions which provide the access to the energy model: 111em_cpu_get() which takes CPU id as an argument and em_pd_get() with device 112pointer as an argument. It depends on the subsystem which interface it is 113going to use, but in case of CPU devices both functions return the same 114performance domain. --- 78 unchanged lines hidden --- | 1292.3 Accessing performance domains 130^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 131 132There are two API functions which provide the access to the energy model: 133em_cpu_get() which takes CPU id as an argument and em_pd_get() with device 134pointer as an argument. It depends on the subsystem which interface it is 135going to use, but in case of CPU devices both functions return the same 136performance domain. --- 78 unchanged lines hidden --- |