106 lines
3.6 KiB
ReStructuredText
106 lines
3.6 KiB
ReStructuredText
=============================
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Subsystem Trace Points: power
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=============================
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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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- 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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- System clock related changes
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- 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 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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::
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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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cpu_frequency_limits "min=%lu max=%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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::
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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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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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::
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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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::
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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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4. PM QoS events
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================
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The PM QoS events are used for QoS add/update/remove request and for
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target/flags update.
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::
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pm_qos_add_request "pm_qos_class=%s value=%d"
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pm_qos_update_request "pm_qos_class=%s value=%d"
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pm_qos_remove_request "pm_qos_class=%s value=%d"
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pm_qos_update_request_timeout "pm_qos_class=%s value=%d, timeout_us=%ld"
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The first parameter gives the QoS class name (e.g. "CPU_DMA_LATENCY").
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The second parameter is value to be added/updated/removed.
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The third parameter is timeout value in usec.
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::
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pm_qos_update_target "action=%s prev_value=%d curr_value=%d"
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pm_qos_update_flags "action=%s prev_value=0x%x curr_value=0x%x"
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The first parameter gives the QoS action name (e.g. "ADD_REQ").
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The second parameter is the previous QoS value.
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The third parameter is the current QoS value to update.
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And, there are also events used for device PM QoS add/update/remove request.
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::
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dev_pm_qos_add_request "device=%s type=%s new_value=%d"
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dev_pm_qos_update_request "device=%s type=%s new_value=%d"
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dev_pm_qos_remove_request "device=%s type=%s new_value=%d"
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The first parameter gives the device name which tries to add/update/remove
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QoS requests.
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The second parameter gives the request type (e.g. "DEV_PM_QOS_RESUME_LATENCY").
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The third parameter is value to be added/updated/removed.
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