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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 Trace API
- -----------------
- A 'cpu' event class gathers the CPU-related events: cpuidle and
- cpufreq.
- 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.
- 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.
- 4. PM QoS events
- ================
- The PM QoS events are used for QoS add/update/remove request and for
- target/flags update.
- pm_qos_add_request "pm_qos_class=%s value=%d"
- pm_qos_update_request "pm_qos_class=%s value=%d"
- pm_qos_remove_request "pm_qos_class=%s value=%d"
- pm_qos_update_request_timeout "pm_qos_class=%s value=%d, timeout_us=%ld"
- The first parameter gives the QoS class name (e.g. "CPU_DMA_LATENCY").
- The second parameter is value to be added/updated/removed.
- The third parameter is timeout value in usec.
- pm_qos_update_target "action=%s prev_value=%d curr_value=%d"
- pm_qos_update_flags "action=%s prev_value=0x%x curr_value=0x%x"
- The first parameter gives the QoS action name (e.g. "ADD_REQ").
- The second parameter is the previous QoS value.
- The third parameter is the current QoS value to update.
- And, there are also events used for device PM QoS add/update/remove request.
- dev_pm_qos_add_request "device=%s type=%s new_value=%d"
- dev_pm_qos_update_request "device=%s type=%s new_value=%d"
- dev_pm_qos_remove_request "device=%s type=%s new_value=%d"
- The first parameter gives the device name which tries to add/update/remove
- QoS requests.
- The second parameter gives the request type (e.g. "DEV_PM_QOS_RESUME_LATENCY").
- The third parameter is value to be added/updated/removed.
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