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Documentation / trace / events-power.txt




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Based on kernel version 3.16. Page generated on 2014-08-06 21:41 EST.

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 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	2. Clocks events
45	================
46	The clock events are used for clock enable/disable and for
47	clock rate change.
48	
49	clock_enable		"%s state=%lu cpu_id=%lu"
50	clock_disable		"%s state=%lu cpu_id=%lu"
51	clock_set_rate		"%s state=%lu cpu_id=%lu"
52	
53	The first parameter gives the clock name (e.g. "gpio1_iclk").
54	The second parameter is '1' for enable, '0' for disable, the target
55	clock rate for set_rate.
56	
57	3. Power domains events
58	=======================
59	The power domain events are used for power domains transitions
60	
61	power_domain_target	"%s state=%lu cpu_id=%lu"
62	
63	The first parameter gives the power domain name (e.g. "mpu_pwrdm").
64	The second parameter is the power domain target state.
65	
66	4. PM QoS events
67	================
68	The PM QoS events are used for QoS add/update/remove request and for
69	target/flags update.
70	
71	pm_qos_add_request                 "pm_qos_class=%s value=%d"
72	pm_qos_update_request              "pm_qos_class=%s value=%d"
73	pm_qos_remove_request              "pm_qos_class=%s value=%d"
74	pm_qos_update_request_timeout      "pm_qos_class=%s value=%d, timeout_us=%ld"
75	
76	The first parameter gives the QoS class name (e.g. "CPU_DMA_LATENCY").
77	The second parameter is value to be added/updated/removed.
78	The third parameter is timeout value in usec.
79	
80	pm_qos_update_target               "action=%s prev_value=%d curr_value=%d"
81	pm_qos_update_flags                "action=%s prev_value=0x%x curr_value=0x%x"
82	
83	The first parameter gives the QoS action name (e.g. "ADD_REQ").
84	The second parameter is the previous QoS value.
85	The third parameter is the current QoS value to update.
86	
87	And, there are also events used for device PM QoS add/update/remove request.
88	
89	dev_pm_qos_add_request             "device=%s type=%s new_value=%d"
90	dev_pm_qos_update_request          "device=%s type=%s new_value=%d"
91	dev_pm_qos_remove_request          "device=%s type=%s new_value=%d"
92	
93	The first parameter gives the device name which tries to add/update/remove
94	QoS requests.
95	The second parameter gives the request type (e.g. "DEV_PM_QOS_RESUME_LATENCY").
96	The third parameter is value to be added/updated/removed.
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