1 2 Subsystem Trace Points: power 3 4The power tracing system captures events related to power transitions 5within 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 12This document describes what each of the tracepoints is and why they 13might be useful. 14 15Cf. include/trace/events/power.h for the events definitions. 16 171. Power state switch events 18============================ 19 201.1 Trace API 21----------------- 22 23A 'cpu' event class gathers the CPU-related events: cpuidle and 24cpufreq. 25 26cpu_idle "state=%lu cpu_id=%lu" 27cpu_frequency "state=%lu cpu_id=%lu" 28cpu_frequency_limits "min=%lu max=%lu cpu_id=%lu" 29 30A suspend event is used to indicate the system going in and out of the 31suspend mode: 32 33machine_suspend "state=%lu" 34 35 36Note: the value of '-1' or '4294967295' for state means an exit from the current state, 37i.e. trace_cpu_idle(4, smp_processor_id()) means that the system 38enters the idle state 4, while trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id()) 39means that the system exits the previous idle state. 40 41The event which has 'state=4294967295' in the trace is very important to the user 42space tools which are using it to detect the end of the current state, and so to 43correctly draw the states diagrams and to calculate accurate statistics etc. 44 452. Clocks events 46================ 47The clock events are used for clock enable/disable and for 48clock rate change. 49 50clock_enable "%s state=%lu cpu_id=%lu" 51clock_disable "%s state=%lu cpu_id=%lu" 52clock_set_rate "%s state=%lu cpu_id=%lu" 53 54The first parameter gives the clock name (e.g. "gpio1_iclk"). 55The second parameter is '1' for enable, '0' for disable, the target 56clock rate for set_rate. 57 583. Power domains events 59======================= 60The power domain events are used for power domains transitions 61 62power_domain_target "%s state=%lu cpu_id=%lu" 63 64The first parameter gives the power domain name (e.g. "mpu_pwrdm"). 65The second parameter is the power domain target state. 66 674. PM QoS events 68================ 69The PM QoS events are used for QoS add/update/remove request and for 70target/flags update. 71 72pm_qos_add_request "pm_qos_class=%s value=%d" 73pm_qos_update_request "pm_qos_class=%s value=%d" 74pm_qos_remove_request "pm_qos_class=%s value=%d" 75pm_qos_update_request_timeout "pm_qos_class=%s value=%d, timeout_us=%ld" 76 77The first parameter gives the QoS class name (e.g. "CPU_DMA_LATENCY"). 78The second parameter is value to be added/updated/removed. 79The third parameter is timeout value in usec. 80 81pm_qos_update_target "action=%s prev_value=%d curr_value=%d" 82pm_qos_update_flags "action=%s prev_value=0x%x curr_value=0x%x" 83 84The first parameter gives the QoS action name (e.g. "ADD_REQ"). 85The second parameter is the previous QoS value. 86The third parameter is the current QoS value to update. 87 88And, there are also events used for device PM QoS add/update/remove request. 89 90dev_pm_qos_add_request "device=%s type=%s new_value=%d" 91dev_pm_qos_update_request "device=%s type=%s new_value=%d" 92dev_pm_qos_remove_request "device=%s type=%s new_value=%d" 93 94The first parameter gives the device name which tries to add/update/remove 95QoS requests. 96The second parameter gives the request type (e.g. "DEV_PM_QOS_RESUME_LATENCY"). 97The third parameter is value to be added/updated/removed. 98