0001 =============================
0002 Subsystem Trace Points: power
0003 =============================
0004
0005 The power tracing system captures events related to power transitions
0006 within the kernel. Broadly speaking there are three major subheadings:
0007
0008 - Power state switch which reports events related to suspend (S-states),
0009 cpuidle (C-states) and cpufreq (P-states)
0010 - System clock related changes
0011 - Power domains related changes and transitions
0012
0013 This document describes what each of the tracepoints is and why they
0014 might be useful.
0015
0016 Cf. include/trace/events/power.h for the events definitions.
0017
0018 1. Power state switch events
0019 ============================
0020
0021 1.1 Trace API
0022 -----------------
0023
0024 A 'cpu' event class gathers the CPU-related events: cpuidle and
0025 cpufreq.
0026 ::
0027
0028 cpu_idle "state=%lu cpu_id=%lu"
0029 cpu_frequency "state=%lu cpu_id=%lu"
0030 cpu_frequency_limits "min=%lu max=%lu cpu_id=%lu"
0031
0032 A suspend event is used to indicate the system going in and out of the
0033 suspend mode:
0034 ::
0035
0036 machine_suspend "state=%lu"
0037
0038
0039 Note: the value of '-1' or '4294967295' for state means an exit from the current state,
0040 i.e. trace_cpu_idle(4, smp_processor_id()) means that the system
0041 enters the idle state 4, while trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id())
0042 means that the system exits the previous idle state.
0043
0044 The event which has 'state=4294967295' in the trace is very important to the user
0045 space tools which are using it to detect the end of the current state, and so to
0046 correctly draw the states diagrams and to calculate accurate statistics etc.
0047
0048 2. Clocks events
0049 ================
0050 The clock events are used for clock enable/disable and for
0051 clock rate change.
0052 ::
0053
0054 clock_enable "%s state=%lu cpu_id=%lu"
0055 clock_disable "%s state=%lu cpu_id=%lu"
0056 clock_set_rate "%s state=%lu cpu_id=%lu"
0057
0058 The first parameter gives the clock name (e.g. "gpio1_iclk").
0059 The second parameter is '1' for enable, '0' for disable, the target
0060 clock rate for set_rate.
0061
0062 3. Power domains events
0063 =======================
0064 The power domain events are used for power domains transitions
0065 ::
0066
0067 power_domain_target "%s state=%lu cpu_id=%lu"
0068
0069 The first parameter gives the power domain name (e.g. "mpu_pwrdm").
0070 The second parameter is the power domain target state.
0071
0072 4. PM QoS events
0073 ================
0074 The PM QoS events are used for QoS add/update/remove request and for
0075 target/flags update.
0076 ::
0077
0078 pm_qos_update_target "action=%s prev_value=%d curr_value=%d"
0079 pm_qos_update_flags "action=%s prev_value=0x%x curr_value=0x%x"
0080
0081 The first parameter gives the QoS action name (e.g. "ADD_REQ").
0082 The second parameter is the previous QoS value.
0083 The third parameter is the current QoS value to update.
0084
0085 There are also events used for device PM QoS add/update/remove request.
0086 ::
0087
0088 dev_pm_qos_add_request "device=%s type=%s new_value=%d"
0089 dev_pm_qos_update_request "device=%s type=%s new_value=%d"
0090 dev_pm_qos_remove_request "device=%s type=%s new_value=%d"
0091
0092 The first parameter gives the device name which tries to add/update/remove
0093 QoS requests.
0094 The second parameter gives the request type (e.g. "DEV_PM_QOS_RESUME_LATENCY").
0095 The third parameter is value to be added/updated/removed.
0096
0097 And, there are events used for CPU latency QoS add/update/remove request.
0098 ::
0099
0100 pm_qos_add_request "value=%d"
0101 pm_qos_update_request "value=%d"
0102 pm_qos_remove_request "value=%d"
0103
0104 The parameter is the value to be added/updated/removed.
