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1da177e4 LT |
1 | /** |
2 | * @file cpu_buffer.c | |
3 | * | |
4 | * @remark Copyright 2002 OProfile authors | |
5 | * @remark Read the file COPYING | |
6 | * | |
7 | * @author John Levon <levon@movementarian.org> | |
8 | * | |
9 | * Each CPU has a local buffer that stores PC value/event | |
10 | * pairs. We also log context switches when we notice them. | |
11 | * Eventually each CPU's buffer is processed into the global | |
12 | * event buffer by sync_buffer(). | |
13 | * | |
14 | * We use a local buffer for two reasons: an NMI or similar | |
15 | * interrupt cannot synchronise, and high sampling rates | |
16 | * would lead to catastrophic global synchronisation if | |
17 | * a global buffer was used. | |
18 | */ | |
19 | ||
20 | #include <linux/sched.h> | |
21 | #include <linux/oprofile.h> | |
22 | #include <linux/vmalloc.h> | |
23 | #include <linux/errno.h> | |
24 | ||
25 | #include "event_buffer.h" | |
26 | #include "cpu_buffer.h" | |
27 | #include "buffer_sync.h" | |
28 | #include "oprof.h" | |
29 | ||
30 | struct oprofile_cpu_buffer cpu_buffer[NR_CPUS] __cacheline_aligned; | |
31 | ||
32 | static void wq_sync_buffer(void *); | |
33 | ||
34 | #define DEFAULT_TIMER_EXPIRE (HZ / 10) | |
35 | static int work_enabled; | |
36 | ||
37 | void free_cpu_buffers(void) | |
38 | { | |
39 | int i; | |
40 | ||
41 | for_each_online_cpu(i) { | |
42 | vfree(cpu_buffer[i].buffer); | |
43 | } | |
44 | } | |
45 | ||
46 | ||
47 | int alloc_cpu_buffers(void) | |
48 | { | |
49 | int i; | |
50 | ||
51 | unsigned long buffer_size = fs_cpu_buffer_size; | |
52 | ||
53 | for_each_online_cpu(i) { | |
54 | struct oprofile_cpu_buffer * b = &cpu_buffer[i]; | |
55 | ||
56 | b->buffer = vmalloc(sizeof(struct op_sample) * buffer_size); | |
57 | if (!b->buffer) | |
58 | goto fail; | |
59 | ||
60 | b->last_task = NULL; | |
61 | b->last_is_kernel = -1; | |
62 | b->tracing = 0; | |
63 | b->buffer_size = buffer_size; | |
64 | b->tail_pos = 0; | |
65 | b->head_pos = 0; | |
66 | b->sample_received = 0; | |
67 | b->sample_lost_overflow = 0; | |
68 | b->cpu = i; | |
69 | INIT_WORK(&b->work, wq_sync_buffer, b); | |
70 | } | |
71 | return 0; | |
72 | ||
73 | fail: | |
74 | free_cpu_buffers(); | |
75 | return -ENOMEM; | |
76 | } | |
77 | ||
78 | ||
79 | void start_cpu_work(void) | |
80 | { | |
81 | int i; | |
82 | ||
83 | work_enabled = 1; | |
84 | ||
85 | for_each_online_cpu(i) { | |
86 | struct oprofile_cpu_buffer * b = &cpu_buffer[i]; | |
87 | ||
88 | /* | |
89 | * Spread the work by 1 jiffy per cpu so they dont all | |
90 | * fire at once. | |
91 | */ | |
92 | schedule_delayed_work_on(i, &b->work, DEFAULT_TIMER_EXPIRE + i); | |
93 | } | |
94 | } | |
95 | ||
96 | ||
97 | void end_cpu_work(void) | |
98 | { | |
99 | int i; | |
100 | ||
101 | work_enabled = 0; | |
102 | ||
103 | for_each_online_cpu(i) { | |
104 | struct oprofile_cpu_buffer * b = &cpu_buffer[i]; | |
105 | ||
106 | cancel_delayed_work(&b->work); | |
107 | } | |
108 | ||
109 | flush_scheduled_work(); | |
110 | } | |
111 | ||
112 | ||
113 | /* Resets the cpu buffer to a sane state. */ | |
114 | void cpu_buffer_reset(struct oprofile_cpu_buffer * cpu_buf) | |
115 | { | |
116 | /* reset these to invalid values; the next sample | |
117 | * collected will populate the buffer with proper | |
118 | * values to initialize the buffer | |
119 | */ | |
120 | cpu_buf->last_is_kernel = -1; | |
121 | cpu_buf->last_task = NULL; | |
122 | } | |
123 | ||
124 | ||
125 | /* compute number of available slots in cpu_buffer queue */ | |
126 | static unsigned long nr_available_slots(struct oprofile_cpu_buffer const * b) | |
127 | { | |
128 | unsigned long head = b->head_pos; | |
129 | unsigned long tail = b->tail_pos; | |
130 | ||
131 | if (tail > head) | |
132 | return (tail - head) - 1; | |
133 | ||
134 | return tail + (b->buffer_size - head) - 1; | |
135 | } | |
136 | ||
137 | ||
138 | static void increment_head(struct oprofile_cpu_buffer * b) | |
139 | { | |
140 | unsigned long new_head = b->head_pos + 1; | |
141 | ||
142 | /* Ensure anything written to the slot before we | |
143 | * increment is visible */ | |
144 | wmb(); | |
145 | ||
146 | if (new_head < b->buffer_size) | |
147 | b->head_pos = new_head; | |
148 | else | |
149 | b->head_pos = 0; | |
150 | } | |
151 | ||
152 | ||
153 | ||
154 | ||
155 | inline static void | |
156 | add_sample(struct oprofile_cpu_buffer * cpu_buf, | |
157 | unsigned long pc, unsigned long event) | |
158 | { | |
159 | struct op_sample * entry = &cpu_buf->buffer[cpu_buf->head_pos]; | |
160 | entry->eip = pc; | |
161 | entry->event = event; | |
162 | increment_head(cpu_buf); | |
163 | } | |
164 | ||
165 | ||
166 | inline static void | |
167 | add_code(struct oprofile_cpu_buffer * buffer, unsigned long value) | |
168 | { | |
169 | add_sample(buffer, ESCAPE_CODE, value); | |
170 | } | |
171 | ||
172 | ||
173 | /* This must be safe from any context. It's safe writing here | |
174 | * because of the head/tail separation of the writer and reader | |
175 | * of the CPU buffer. | |
176 | * | |
177 | * is_kernel is needed because on some architectures you cannot | |
178 | * tell if you are in kernel or user space simply by looking at | |
179 | * pc. We tag this in the buffer by generating kernel enter/exit | |
180 | * events whenever is_kernel changes | |
181 | */ | |
182 | static int log_sample(struct oprofile_cpu_buffer * cpu_buf, unsigned long pc, | |
183 | int is_kernel, unsigned long event) | |
184 | { | |
185 | struct task_struct * task; | |
186 | ||
187 | cpu_buf->sample_received++; | |
188 | ||
189 | if (nr_available_slots(cpu_buf) < 3) { | |
190 | cpu_buf->sample_lost_overflow++; | |
191 | return 0; | |
192 | } | |
193 | ||
194 | is_kernel = !!is_kernel; | |
195 | ||
196 | task = current; | |
197 | ||
198 | /* notice a switch from user->kernel or vice versa */ | |
199 | if (cpu_buf->last_is_kernel != is_kernel) { | |
200 | cpu_buf->last_is_kernel = is_kernel; | |
201 | add_code(cpu_buf, is_kernel); | |
202 | } | |
203 | ||
204 | /* notice a task switch */ | |
205 | if (cpu_buf->last_task != task) { | |
206 | cpu_buf->last_task = task; | |
207 | add_code(cpu_buf, (unsigned long)task); | |
208 | } | |
209 | ||
210 | add_sample(cpu_buf, pc, event); | |
211 | return 1; | |
212 | } | |
213 | ||
214 | static int oprofile_begin_trace(struct oprofile_cpu_buffer * cpu_buf) | |
215 | { | |
216 | if (nr_available_slots(cpu_buf) < 4) { | |
217 | cpu_buf->sample_lost_overflow++; | |
218 | return 0; | |
219 | } | |
220 | ||
221 | add_code(cpu_buf, CPU_TRACE_BEGIN); | |
222 | cpu_buf->tracing = 1; | |
223 | return 1; | |
224 | } | |
225 | ||
226 | ||
227 | static void oprofile_end_trace(struct oprofile_cpu_buffer * cpu_buf) | |
228 | { | |
229 | cpu_buf->tracing = 0; | |
230 | } | |
231 | ||
232 | ||
233 | void oprofile_add_sample(struct pt_regs * const regs, unsigned long event) | |
234 | { | |
235 | struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()]; | |
236 | unsigned long pc = profile_pc(regs); | |
237 | int is_kernel = !user_mode(regs); | |
238 | ||
239 | if (!backtrace_depth) { | |
240 | log_sample(cpu_buf, pc, is_kernel, event); | |
241 | return; | |
242 | } | |
243 | ||
244 | if (!oprofile_begin_trace(cpu_buf)) | |
245 | return; | |
246 | ||
247 | /* if log_sample() fail we can't backtrace since we lost the source | |
248 | * of this event */ | |
249 | if (log_sample(cpu_buf, pc, is_kernel, event)) | |
250 | oprofile_ops.backtrace(regs, backtrace_depth); | |
251 | oprofile_end_trace(cpu_buf); | |
252 | } | |
253 | ||
254 | ||
255 | void oprofile_add_pc(unsigned long pc, int is_kernel, unsigned long event) | |
256 | { | |
257 | struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()]; | |
258 | log_sample(cpu_buf, pc, is_kernel, event); | |
259 | } | |
260 | ||
261 | ||
262 | void oprofile_add_trace(unsigned long pc) | |
263 | { | |
264 | struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()]; | |
265 | ||
266 | if (!cpu_buf->tracing) | |
267 | return; | |
268 | ||
269 | if (nr_available_slots(cpu_buf) < 1) { | |
270 | cpu_buf->tracing = 0; | |
271 | cpu_buf->sample_lost_overflow++; | |
272 | return; | |
273 | } | |
274 | ||
275 | /* broken frame can give an eip with the same value as an escape code, | |
276 | * abort the trace if we get it */ | |
277 | if (pc == ESCAPE_CODE) { | |
278 | cpu_buf->tracing = 0; | |
279 | cpu_buf->backtrace_aborted++; | |
280 | return; | |
281 | } | |
282 | ||
283 | add_sample(cpu_buf, pc, 0); | |
284 | } | |
285 | ||
286 | ||
287 | ||
288 | /* | |
289 | * This serves to avoid cpu buffer overflow, and makes sure | |
290 | * the task mortuary progresses | |
291 | * | |
292 | * By using schedule_delayed_work_on and then schedule_delayed_work | |
293 | * we guarantee this will stay on the correct cpu | |
294 | */ | |
295 | static void wq_sync_buffer(void * data) | |
296 | { | |
297 | struct oprofile_cpu_buffer * b = data; | |
298 | if (b->cpu != smp_processor_id()) { | |
299 | printk("WQ on CPU%d, prefer CPU%d\n", | |
300 | smp_processor_id(), b->cpu); | |
301 | } | |
302 | sync_buffer(b->cpu); | |
303 | ||
304 | /* don't re-add the work if we're shutting down */ | |
305 | if (work_enabled) | |
306 | schedule_delayed_work(&b->work, DEFAULT_TIMER_EXPIRE); | |
307 | } |