| Jean Pihet | 4b95f13 | 2011-01-05 19:49:02 +0100 | [diff] [blame] | 1 | |
| 2 | Subsystem Trace Points: power |
| 3 | |
| 4 | The power tracing system captures events related to power transitions |
| 5 | within the kernel. Broadly speaking there are three major subheadings: |
| 6 | |
| 7 | o Power state switch which reports events related to suspend (S-states), |
| 8 | cpuidle (C-states) and cpufreq (P-states) |
| 9 | o System clock related changes |
| 10 | o Power domains related changes and transitions |
| 11 | |
| 12 | This document describes what each of the tracepoints is and why they |
| 13 | might be useful. |
| 14 | |
| 15 | Cf. include/trace/events/power.h for the events definitions. |
| 16 | |
| 17 | 1. Power state switch events |
| 18 | ============================ |
| 19 | |
| 20 | 1.1 New trace API |
| 21 | ----------------- |
| 22 | |
| 23 | A 'cpu' event class gathers the CPU-related events: cpuidle and |
| 24 | cpufreq. |
| 25 | |
| 26 | cpu_idle "state=%lu cpu_id=%lu" |
| 27 | cpu_frequency "state=%lu cpu_id=%lu" |
| 28 | |
| 29 | A suspend event is used to indicate the system going in and out of the |
| 30 | suspend mode: |
| 31 | |
| 32 | machine_suspend "state=%lu" |
| 33 | |
| 34 | |
| 35 | Note: the value of '-1' or '4294967295' for state means an exit from the current state, |
| 36 | i.e. trace_cpu_idle(4, smp_processor_id()) means that the system |
| 37 | enters the idle state 4, while trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id()) |
| 38 | means that the system exits the previous idle state. |
| 39 | |
| 40 | The event which has 'state=4294967295' in the trace is very important to the user |
| 41 | space tools which are using it to detect the end of the current state, and so to |
| 42 | correctly draw the states diagrams and to calculate accurate statistics etc. |
| 43 | |
| 44 | 1.2 DEPRECATED trace API |
| 45 | ------------------------ |
| 46 | |
| 47 | A new Kconfig option CONFIG_EVENT_POWER_TRACING_DEPRECATED with the default value of |
| 48 | 'y' has been created. This allows the legacy trace power API to be used conjointly |
| 49 | with the new trace API. |
| 50 | The Kconfig option, the old trace API (in include/trace/events/power.h) and the |
| 51 | old trace points will disappear in a future release (namely 2.6.41). |
| 52 | |
| 53 | power_start "type=%lu state=%lu cpu_id=%lu" |
| 54 | power_frequency "type=%lu state=%lu cpu_id=%lu" |
| 55 | power_end "cpu_id=%lu" |
| 56 | |
| 57 | The 'type' parameter takes one of those macros: |
| 58 | . POWER_NONE = 0, |
| 59 | . POWER_CSTATE = 1, /* C-State */ |
| 60 | . POWER_PSTATE = 2, /* Fequency change or DVFS */ |
| 61 | |
| 62 | The 'state' parameter is set depending on the type: |
| 63 | . Target C-state for type=POWER_CSTATE, |
| 64 | . Target frequency for type=POWER_PSTATE, |
| 65 | |
| 66 | power_end is used to indicate the exit of a state, corresponding to the latest |
| 67 | power_start event. |
| 68 | |
| 69 | 2. Clocks events |
| 70 | ================ |
| 71 | The clock events are used for clock enable/disable and for |
| 72 | clock rate change. |
| 73 | |
| 74 | clock_enable "%s state=%lu cpu_id=%lu" |
| 75 | clock_disable "%s state=%lu cpu_id=%lu" |
| 76 | clock_set_rate "%s state=%lu cpu_id=%lu" |
| 77 | |
| 78 | The first parameter gives the clock name (e.g. "gpio1_iclk"). |
| 79 | The second parameter is '1' for enable, '0' for disable, the target |
| 80 | clock rate for set_rate. |
| 81 | |
| 82 | 3. Power domains events |
| 83 | ======================= |
| 84 | The power domain events are used for power domains transitions |
| 85 | |
| 86 | power_domain_target "%s state=%lu cpu_id=%lu" |
| 87 | |
| 88 | The first parameter gives the power domain name (e.g. "mpu_pwrdm"). |
| 89 | The second parameter is the power domain target state. |
| 90 | |