| 1 | ============================= |
| 2 | Subsystem Trace Points: power |
| 3 | ============================= |
| 4 | |
| 5 | The power tracing system captures events related to power transitions |
| 6 | within 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 | |
| 13 | This document describes what each of the tracepoints is and why they |
| 14 | might be useful. |
| 15 | |
| 16 | Cf. include/trace/events/power.h for the events definitions. |
| 17 | |
| 18 | 1. Power state switch events |
| 19 | ============================ |
| 20 | |
| 21 | 1.1 Trace API |
| 22 | ----------------- |
| 23 | |
| 24 | A 'cpu' event class gathers the CPU-related events: cpuidle and |
| 25 | cpufreq. |
| 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 | |
| 32 | A suspend event is used to indicate the system going in and out of the |
| 33 | suspend mode: |
| 34 | :: |
| 35 | |
| 36 | machine_suspend "state=%lu" |
| 37 | |
| 38 | |
| 39 | Note: the value of '-1' or '4294967295' for state means an exit from the current state, |
| 40 | i.e. trace_cpu_idle(4, smp_processor_id()) means that the system |
| 41 | enters the idle state 4, while trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id()) |
| 42 | means that the system exits the previous idle state. |
| 43 | |
| 44 | The event which has 'state=4294967295' in the trace is very important to the user |
| 45 | space tools which are using it to detect the end of the current state, and so to |
| 46 | correctly draw the states diagrams and to calculate accurate statistics etc. |
| 47 | |
| 48 | 2. Clocks events |
| 49 | ================ |
| 50 | The clock events are used for clock enable/disable and for |
| 51 | clock 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 | |
| 58 | The first parameter gives the clock name (e.g. "gpio1_iclk"). |
| 59 | The second parameter is '1' for enable, '0' for disable, the target |
| 60 | clock rate for set_rate. |
| 61 | |
| 62 | 3. Power domains events |
| 63 | ======================= |
| 64 | The power domain events are used for power domains transitions |
| 65 | :: |
| 66 | |
| 67 | power_domain_target "%s state=%lu cpu_id=%lu" |
| 68 | |
| 69 | The first parameter gives the power domain name (e.g. "mpu_pwrdm"). |
| 70 | The second parameter is the power domain target state. |
| 71 | |
| 72 | 4. PM QoS events |
| 73 | ================ |
| 74 | The PM QoS events are used for QoS add/update/remove request and for |
| 75 | target/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 | |
| 81 | The first parameter gives the QoS action name (e.g. "ADD_REQ"). |
| 82 | The second parameter is the previous QoS value. |
| 83 | The third parameter is the current QoS value to update. |
| 84 | |
| 85 | There 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 | |
| 92 | The first parameter gives the device name which tries to add/update/remove |
| 93 | QoS requests. |
| 94 | The second parameter gives the request type (e.g. "DEV_PM_QOS_RESUME_LATENCY"). |
| 95 | The third parameter is value to be added/updated/removed. |
| 96 | |
| 97 | And, 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 | |
| 104 | The parameter is the value to be added/updated/removed. |