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- Subsystem Trace Points: power
-The power tracing system captures events related to power transitions
-within the kernel. Broadly speaking there are three major subheadings:
- o Power state switch which reports events related to suspend (S-states),
- cpuidle (C-states) and cpufreq (P-states)
- o System clock related changes
- o Power domains related changes and transitions
-This document describes what each of the tracepoints is and why they
-might be useful.
-Cf. include/trace/events/power.h for the events definitions.
-1. Power state switch events
-1.1 New trace API
-A 'cpu' event class gathers the CPU-related events: cpuidle and
-cpu_idle "state=%lu cpu_id=%lu"
-cpu_frequency "state=%lu cpu_id=%lu"
-A suspend event is used to indicate the system going in and out of the
-suspend mode:
-machine_suspend "state=%lu"
-Note: the value of '-1' or '4294967295' for state means an exit from the current state,
-i.e. trace_cpu_idle(4, smp_processor_id()) means that the system
-enters the idle state 4, while trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id())
-means that the system exits the previous idle state.
-The event which has 'state=4294967295' in the trace is very important to the user
-space tools which are using it to detect the end of the current state, and so to
-correctly draw the states diagrams and to calculate accurate statistics etc.
-A new Kconfig option CONFIG_EVENT_POWER_TRACING_DEPRECATED with the default value of
-'y' has been created. This allows the legacy trace power API to be used conjointly
-with the new trace API.
-The Kconfig option, the old trace API (in include/trace/events/power.h) and the
-old trace points will disappear in a future release (namely 2.6.41).
-power_start "type=%lu state=%lu cpu_id=%lu"
-power_frequency "type=%lu state=%lu cpu_id=%lu"
-power_end "cpu_id=%lu"
-The 'type' parameter takes one of those macros:
- . POWER_NONE = 0,
- . POWER_CSTATE = 1, /* C-State */
- . POWER_PSTATE = 2, /* Frequency change or DVFS */
-The 'state' parameter is set depending on the type:
- . Target C-state for type=POWER_CSTATE,
- . Target frequency for type=POWER_PSTATE,
-power_end is used to indicate the exit of a state, corresponding to the latest
-power_start event.
-2. Clocks events
-The clock events are used for clock enable/disable and for
-clock rate change.
-clock_enable "%s state=%lu cpu_id=%lu"
-clock_disable "%s state=%lu cpu_id=%lu"
-clock_set_rate "%s state=%lu cpu_id=%lu"
-The first parameter gives the clock name (e.g. "gpio1_iclk").
-The second parameter is '1' for enable, '0' for disable, the target
-clock rate for set_rate.
-3. Power domains events
-The power domain events are used for power domains transitions
-power_domain_target "%s state=%lu cpu_id=%lu"
-The first parameter gives the power domain name (e.g. "mpu_pwrdm").
-The second parameter is the power domain target state.