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1=============================2Subsystem Trace Points: power3=============================4 5The power tracing system captures events related to power transitions6within the kernel. Broadly speaking there are three major subheadings:7 8 - Power state switch which reports events related to suspend (S-states),9 cpuidle (C-states) and cpufreq (P-states)10 - System clock related changes11 - Power domains related changes and transitions12 13This document describes what each of the tracepoints is and why they14might be useful.15 16Cf. include/trace/events/power.h for the events definitions.17 181. Power state switch events19============================20 211.1 Trace API22-----------------23 24A 'cpu' event class gathers the CPU-related events: cpuidle and25cpufreq.26::27 28 cpu_idle "state=%lu cpu_id=%lu"29 cpu_frequency "state=%lu cpu_id=%lu"30 cpu_frequency_limits "min=%lu max=%lu cpu_id=%lu"31 32A suspend event is used to indicate the system going in and out of the33suspend mode:34::35 36 machine_suspend "state=%lu"37 38 39Note: the value of '-1' or '4294967295' for state means an exit from the current state,40i.e. trace_cpu_idle(4, smp_processor_id()) means that the system41enters the idle state 4, while trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id())42means that the system exits the previous idle state.43 44The event which has 'state=4294967295' in the trace is very important to the user45space tools which are using it to detect the end of the current state, and so to46correctly draw the states diagrams and to calculate accurate statistics etc.47 482. Clocks events49================50The clock events are used for clock enable/disable and for51clock rate change.52::53 54 clock_enable "%s state=%lu cpu_id=%lu"55 clock_disable "%s state=%lu cpu_id=%lu"56 clock_set_rate "%s state=%lu cpu_id=%lu"57 58The first parameter gives the clock name (e.g. "gpio1_iclk").59The second parameter is '1' for enable, '0' for disable, the target60clock rate for set_rate.61 623. Power domains events63=======================64The power domain events are used for power domains transitions65::66 67 power_domain_target "%s state=%lu cpu_id=%lu"68 69The first parameter gives the power domain name (e.g. "mpu_pwrdm").70The second parameter is the power domain target state.71 724. PM QoS events73================74The PM QoS events are used for QoS add/update/remove request and for75target/flags update.76::77 78 pm_qos_update_target "action=%s prev_value=%d curr_value=%d"79 pm_qos_update_flags "action=%s prev_value=0x%x curr_value=0x%x"80 81The first parameter gives the QoS action name (e.g. "ADD_REQ").82The second parameter is the previous QoS value.83The third parameter is the current QoS value to update.84 85There are also events used for device PM QoS add/update/remove request.86::87 88 dev_pm_qos_add_request "device=%s type=%s new_value=%d"89 dev_pm_qos_update_request "device=%s type=%s new_value=%d"90 dev_pm_qos_remove_request "device=%s type=%s new_value=%d"91 92The first parameter gives the device name which tries to add/update/remove93QoS requests.94The second parameter gives the request type (e.g. "DEV_PM_QOS_RESUME_LATENCY").95The third parameter is value to be added/updated/removed.96 97And, there are events used for CPU latency QoS add/update/remove request.98::99 100 pm_qos_add_request "value=%d"101 pm_qos_update_request "value=%d"102 pm_qos_remove_request "value=%d"103 104The parameter is the value to be added/updated/removed.105