2011-01-06 02:49:02 +08:00
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Subsystem Trace Points: power
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The power tracing system captures events related to power transitions
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within the kernel. Broadly speaking there are three major subheadings:
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o Power state switch which reports events related to suspend (S-states),
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cpuidle (C-states) and cpufreq (P-states)
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o System clock related changes
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o Power domains related changes and transitions
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This document describes what each of the tracepoints is and why they
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might be useful.
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Cf. include/trace/events/power.h for the events definitions.
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1. Power state switch events
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============================
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1.1 New trace API
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-----------------
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A 'cpu' event class gathers the CPU-related events: cpuidle and
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cpufreq.
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cpu_idle "state=%lu cpu_id=%lu"
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cpu_frequency "state=%lu cpu_id=%lu"
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A suspend event is used to indicate the system going in and out of the
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suspend mode:
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machine_suspend "state=%lu"
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Note: the value of '-1' or '4294967295' for state means an exit from the current state,
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i.e. trace_cpu_idle(4, smp_processor_id()) means that the system
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enters the idle state 4, while trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id())
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means that the system exits the previous idle state.
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The event which has 'state=4294967295' in the trace is very important to the user
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space tools which are using it to detect the end of the current state, and so to
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correctly draw the states diagrams and to calculate accurate statistics etc.
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1.2 DEPRECATED trace API
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------------------------
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A new Kconfig option CONFIG_EVENT_POWER_TRACING_DEPRECATED with the default value of
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'y' has been created. This allows the legacy trace power API to be used conjointly
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with the new trace API.
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The Kconfig option, the old trace API (in include/trace/events/power.h) and the
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old trace points will disappear in a future release (namely 2.6.41).
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power_start "type=%lu state=%lu cpu_id=%lu"
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power_frequency "type=%lu state=%lu cpu_id=%lu"
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power_end "cpu_id=%lu"
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The 'type' parameter takes one of those macros:
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. POWER_NONE = 0,
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. POWER_CSTATE = 1, /* C-State */
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2012-02-16 22:19:56 +08:00
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. POWER_PSTATE = 2, /* Frequency change or DVFS */
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2011-01-06 02:49:02 +08:00
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The 'state' parameter is set depending on the type:
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. Target C-state for type=POWER_CSTATE,
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. Target frequency for type=POWER_PSTATE,
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power_end is used to indicate the exit of a state, corresponding to the latest
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power_start event.
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2. Clocks events
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================
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The clock events are used for clock enable/disable and for
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clock rate change.
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clock_enable "%s state=%lu cpu_id=%lu"
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clock_disable "%s state=%lu cpu_id=%lu"
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clock_set_rate "%s state=%lu cpu_id=%lu"
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The first parameter gives the clock name (e.g. "gpio1_iclk").
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The second parameter is '1' for enable, '0' for disable, the target
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clock rate for set_rate.
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3. Power domains events
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=======================
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The power domain events are used for power domains transitions
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power_domain_target "%s state=%lu cpu_id=%lu"
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The first parameter gives the power domain name (e.g. "mpu_pwrdm").
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The second parameter is the power domain target state.
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