blob: e9b1772a3a28cdfb7253faac3f2d24447946dd4a [file] [log] [blame]
Linus Torvalds1da177e2005-04-16 15:20:36 -07001/**
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
30struct oprofile_cpu_buffer cpu_buffer[NR_CPUS] __cacheline_aligned;
31
32static void wq_sync_buffer(void *);
33
34#define DEFAULT_TIMER_EXPIRE (HZ / 10)
35static int work_enabled;
36
37void 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
47int 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
73fail:
74 free_cpu_buffers();
75 return -ENOMEM;
76}
77
78
79void 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
97void 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. */
114void 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 */
126static 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
138static 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
155inline static void
156add_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
166inline static void
167add_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 */
182static 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
214static 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
227static void oprofile_end_trace(struct oprofile_cpu_buffer * cpu_buf)
228{
229 cpu_buf->tracing = 0;
230}
231
232
233void 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
255void 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
262void 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 */
295static 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}