events-power.rst

  1=============================
  2Subsystem Trace Points: power
  3=============================
  4
  5The power tracing system captures events related to power transitions
  6within 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 changes
 11  - Power domains related changes and transitions
 12
 13This document describes what each of the tracepoints is and why they
 14might be useful.
 15
 16Cf. include/trace/events/power.h for the events definitions.
 17
 181. Power state switch events
 19============================
 20
 211.1 Trace API
 22-----------------
 23
 24A 'cpu' event class gathers the CPU-related events: cpuidle and
 25cpufreq.
 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 the
 33suspend 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 system
 41enters 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 user
 45space tools which are using it to detect the end of the current state, and so to
 46correctly draw the states diagrams and to calculate accurate statistics etc.
 47
 482. Clocks events
 49================
 50The clock events are used for clock enable/disable and for
 51clock 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 target
 60clock rate for set_rate.
 61
 623. Power domains events
 63=======================
 64The power domain events are used for power domains transitions
 65::
 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 events
 73================
 74The PM QoS events are used for QoS add/update/remove request and for
 75target/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/remove
 93QoS 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.