Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 2 Subsystem Trace Points: power 3 4 The power tracing system captures events related to power transitions 5 within the kernel. Broadly speaking there are three major subheadings: 6 7 o Power state switch which reports events related to suspend (S-states), 8 cpuidle (C-states) and cpufreq (P-states) 9 o System clock related changes 10 o Power domains related changes and transitions 11 12 This document describes what each of the tracepoints is and why they 13 might be useful. 14 15 Cf. include/trace/events/power.h for the events definitions. 16 17 1. Power state switch events 18 ============================ 19 20 1.1 Trace API 21 ----------------- 22 23 A 'cpu' event class gathers the CPU-related events: cpuidle and 24 cpufreq. 25 26 cpu_idle "state=%lu cpu_id=%lu" 27 cpu_frequency "state=%lu cpu_id=%lu" 28 29 A suspend event is used to indicate the system going in and out of the 30 suspend mode: 31 32 machine_suspend "state=%lu" 33 34 35 Note: the value of '-1' or '4294967295' for state means an exit from the current state, 36 i.e. trace_cpu_idle(4, smp_processor_id()) means that the system 37 enters the idle state 4, while trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id()) 38 means that the system exits the previous idle state. 39 40 The event which has 'state=4294967295' in the trace is very important to the user 41 space tools which are using it to detect the end of the current state, and so to 42 correctly draw the states diagrams and to calculate accurate statistics etc. 43 44 2. Clocks events 45 ================ 46 The clock events are used for clock enable/disable and for 47 clock rate change. 48 49 clock_enable "%s state=%lu cpu_id=%lu" 50 clock_disable "%s state=%lu cpu_id=%lu" 51 clock_set_rate "%s state=%lu cpu_id=%lu" 52 53 The first parameter gives the clock name (e.g. "gpio1_iclk"). 54 The second parameter is '1' for enable, '0' for disable, the target 55 clock rate for set_rate. 56 57 3. Power domains events 58 ======================= 59 The power domain events are used for power domains transitions 60 61 power_domain_target "%s state=%lu cpu_id=%lu" 62 63 The first parameter gives the power domain name (e.g. "mpu_pwrdm"). 64 The second parameter is the power domain target state. 65 66 4. PM QoS events 67 ================ 68 The PM QoS events are used for QoS add/update/remove request and for 69 target/flags update. 70 71 pm_qos_add_request "pm_qos_class=%s value=%d" 72 pm_qos_update_request "pm_qos_class=%s value=%d" 73 pm_qos_remove_request "pm_qos_class=%s value=%d" 74 pm_qos_update_request_timeout "pm_qos_class=%s value=%d, timeout_us=%ld" 75 76 The first parameter gives the QoS class name (e.g. "CPU_DMA_LATENCY"). 77 The second parameter is value to be added/updated/removed. 78 The third parameter is timeout value in usec. 79 80 pm_qos_update_target "action=%s prev_value=%d curr_value=%d" 81 pm_qos_update_flags "action=%s prev_value=0x%x curr_value=0x%x" 82 83 The first parameter gives the QoS action name (e.g. "ADD_REQ"). 84 The second parameter is the previous QoS value. 85 The third parameter is the current QoS value to update. 86 87 And, there are also events used for device PM QoS add/update/remove request. 88 89 dev_pm_qos_add_request "device=%s type=%s new_value=%d" 90 dev_pm_qos_update_request "device=%s type=%s new_value=%d" 91 dev_pm_qos_remove_request "device=%s type=%s new_value=%d" 92 93 The first parameter gives the device name which tries to add/update/remove 94 QoS requests. 95 The second parameter gives the request type (e.g. "DEV_PM_QOS_RESUME_LATENCY"). 96 The third parameter is value to be added/updated/removed.