1 Deterministic Automata Instrumentation
2 ======================================
3
4 The RV monitor file created by dot2k, with the name "$MODEL_NAME.c"
5 includes a section dedicated to instrumentation.
6
7 In the example of the wip.dot monitor created on [1], it will look like::
8
9 /*
10 * This is the instrumentation part of the monitor.
11 *
12 * This is the section where manual work is required. Here the kernel events
13 * are translated into model's event.
14 *
15 */
16 static void handle_preempt_disable(void *data, /* XXX: fill header */)
17 {
18 da_handle_event_wip(preempt_disable_wip);
19 }
20
21 static void handle_preempt_enable(void *data, /* XXX: fill header */)
22 {
23 da_handle_event_wip(preempt_enable_wip);
24 }
25
26 static void handle_sched_waking(void *data, /* XXX: fill header */)
27 {
28 da_handle_event_wip(sched_waking_wip);
29 }
30
31 static int enable_wip(void)
32 {
33 int retval;
34
35 retval = da_monitor_init_wip();
36 if (retval)
37 return retval;
38
39 rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_preempt_disable);
40 rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_preempt_enable);
41 rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_sched_waking);
42
43 return 0;
44 }
45
46 The comment at the top of the section explains the general idea: the
47 instrumentation section translates *kernel events* into the *model's
48 event*.
49
50 Tracing callback functions
51 --------------------------
52
53 The first three functions are the starting point of the callback *handler
54 functions* for each of the three events from the wip model. The developer
55 does not necessarily need to use them: they are just starting points.
56
57 Using the example of::
58
59 void handle_preempt_disable(void *data, /* XXX: fill header */)
60 {
61 da_handle_event_wip(preempt_disable_wip);
62 }
63
64 The preempt_disable event from the model connects directly to the
65 preemptirq:preempt_disable. The preemptirq:preempt_disable event
66 has the following signature, from include/trace/events/preemptirq.h::
67
68 TP_PROTO(unsigned long ip, unsigned long parent_ip)
69
70 Hence, the handle_preempt_disable() function will look like::
71
72 void handle_preempt_disable(void *data, unsigned long ip, unsigned long parent_ip)
73
74 In this case, the kernel event translates one to one with the automata
75 event, and indeed, no other change is required for this function.
76
77 The next handler function, handle_preempt_enable() has the same argument
78 list from the handle_preempt_disable(). The difference is that the
79 preempt_enable event will be used to synchronize the system to the model.
80
81 Initially, the *model* is placed in the initial state. However, the *system*
82 might or might not be in the initial state. The monitor cannot start
83 processing events until it knows that the system has reached the initial state.
84 Otherwise, the monitor and the system could be out-of-sync.
85
86 Looking at the automata definition, it is possible to see that the system
87 and the model are expected to return to the initial state after the
88 preempt_enable execution. Hence, it can be used to synchronize the
89 system and the model at the initialization of the monitoring section.
90
91 The start is informed via a special handle function, the
92 "da_handle_start_event_$(MONITOR_NAME)(event)", in this case::
93
94 da_handle_start_event_wip(preempt_enable_wip);
95
96 So, the callback function will look like::
97
98 void handle_preempt_enable(void *data, unsigned long ip, unsigned long parent_ip)
99 {
100 da_handle_start_event_wip(preempt_enable_wip);
101 }
102
103 Finally, the "handle_sched_waking()" will look like::
104
105 void handle_sched_waking(void *data, struct task_struct *task)
106 {
107 da_handle_event_wip(sched_waking_wip);
108 }
109
110 And the explanation is left for the reader as an exercise.
111
112 enable and disable functions
113 ----------------------------
114
115 dot2k automatically creates two special functions::
116
117 enable_$(MONITOR_NAME)()
118 disable_$(MONITOR_NAME)()
119
120 These functions are called when the monitor is enabled and disabled,
121 respectively.
122
123 They should be used to *attach* and *detach* the instrumentation to the running
124 system. The developer must add to the relative function all that is needed to
125 *attach* and *detach* its monitor to the system.
126
127 For the wip case, these functions were named::
128
129 enable_wip()
130 disable_wip()
131
132 But no change was required because: by default, these functions *attach* and
133 *detach* the tracepoints_to_attach, which was enough for this case.
134
135 Instrumentation helpers
136 -----------------------
137
138 To complete the instrumentation, the *handler functions* need to be attached to a
139 kernel event, at the monitoring enable phase.
140
141 The RV interface also facilitates this step. For example, the macro "rv_attach_trace_probe()"
142 is used to connect the wip model events to the relative kernel event. dot2k automatically
143 adds "rv_attach_trace_probe()" function call for each model event in the enable phase, as
144 a suggestion.
145
146 For example, from the wip sample model::
147
148 static int enable_wip(void)
149 {
150 int retval;
151
152 retval = da_monitor_init_wip();
153 if (retval)
154 return retval;
155
156 rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_preempt_enable);
157 rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_sched_waking);
158 rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_preempt_disable);
159
160 return 0;
161 }
162
163 The probes then need to be detached at the disable phase.
164
165 [1] The wip model is presented in::
166
167 Documentation/trace/rv/deterministic_automata.rst
168
169 The wip monitor is presented in::
170
171 Documentation/trace/rv/da_monitor_synthesis.rst
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