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diff --git a/Documentation/trace/events-power.rst b/Documentation/trace/events-power.rst new file mode 100644 index 000000000..f45bf11fa --- /dev/null +++ b/Documentation/trace/events-power.rst @@ -0,0 +1,104 @@ +============================= +Subsystem Trace Points: power +============================= + +The power tracing system captures events related to power transitions +within the kernel. Broadly speaking there are three major subheadings: + + - Power state switch which reports events related to suspend (S-states), + cpuidle (C-states) and cpufreq (P-states) + - System clock related changes + - 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" + cpu_frequency_limits "min=%lu max=%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_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. + +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. + +And, there are events used for CPU latency QoS add/update/remove request. +:: + + pm_qos_add_request "value=%d" + pm_qos_update_request "value=%d" + pm_qos_remove_request "value=%d" + +The parameter is the value to be added/updated/removed. |