c93d3d2640ab884b2a4d43a4339afd2613cd149d
[linux-2.6.git] / drivers / oprofile / cpu_buffer.c
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(struct work_struct *work);
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 int alloc_cpu_buffers(void)
46 {
47         int i;
48  
49         unsigned long buffer_size = fs_cpu_buffer_size;
50  
51         for_each_online_cpu(i) {
52                 struct oprofile_cpu_buffer * b = &cpu_buffer[i];
53  
54                 b->buffer = vmalloc_node(sizeof(struct op_sample) * buffer_size,
55                         cpu_to_node(i));
56                 if (!b->buffer)
57                         goto fail;
58  
59                 b->last_task = NULL;
60                 b->last_is_kernel = -1;
61                 b->tracing = 0;
62                 b->buffer_size = buffer_size;
63                 b->tail_pos = 0;
64                 b->head_pos = 0;
65                 b->sample_received = 0;
66                 b->sample_lost_overflow = 0;
67                 b->backtrace_aborted = 0;
68                 b->sample_invalid_eip = 0;
69                 b->cpu = i;
70                 INIT_DELAYED_WORK(&b->work, wq_sync_buffer);
71         }
72         return 0;
73
74 fail:
75         free_cpu_buffers();
76         return -ENOMEM;
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 void end_cpu_work(void)
97 {
98         int i;
99
100         work_enabled = 0;
101
102         for_each_online_cpu(i) {
103                 struct oprofile_cpu_buffer * b = &cpu_buffer[i];
104
105                 cancel_delayed_work(&b->work);
106         }
107
108         flush_scheduled_work();
109 }
110
111 /* Resets the cpu buffer to a sane state. */
112 void cpu_buffer_reset(struct oprofile_cpu_buffer * cpu_buf)
113 {
114         /* reset these to invalid values; the next sample
115          * collected will populate the buffer with proper
116          * values to initialize the buffer
117          */
118         cpu_buf->last_is_kernel = -1;
119         cpu_buf->last_task = NULL;
120 }
121
122 /* compute number of available slots in cpu_buffer queue */
123 static unsigned long nr_available_slots(struct oprofile_cpu_buffer const * b)
124 {
125         unsigned long head = b->head_pos;
126         unsigned long tail = b->tail_pos;
127
128         if (tail > head)
129                 return (tail - head) - 1;
130
131         return tail + (b->buffer_size - head) - 1;
132 }
133
134 static void increment_head(struct oprofile_cpu_buffer * b)
135 {
136         unsigned long new_head = b->head_pos + 1;
137
138         /* Ensure anything written to the slot before we
139          * increment is visible */
140         wmb();
141
142         if (new_head < b->buffer_size)
143                 b->head_pos = new_head;
144         else
145                 b->head_pos = 0;
146 }
147
148 static inline void
149 add_sample(struct oprofile_cpu_buffer * cpu_buf,
150            unsigned long pc, unsigned long event)
151 {
152         struct op_sample * entry = &cpu_buf->buffer[cpu_buf->head_pos];
153         entry->eip = pc;
154         entry->event = event;
155         increment_head(cpu_buf);
156 }
157
158 static inline void
159 add_code(struct oprofile_cpu_buffer * buffer, unsigned long value)
160 {
161         add_sample(buffer, ESCAPE_CODE, value);
162 }
163
164 /* This must be safe from any context. It's safe writing here
165  * because of the head/tail separation of the writer and reader
166  * of the CPU buffer.
167  *
168  * is_kernel is needed because on some architectures you cannot
169  * tell if you are in kernel or user space simply by looking at
170  * pc. We tag this in the buffer by generating kernel enter/exit
171  * events whenever is_kernel changes
172  */
173 static int log_sample(struct oprofile_cpu_buffer * cpu_buf, unsigned long pc,
174                       int is_kernel, unsigned long event)
175 {
176         struct task_struct * task;
177
178         cpu_buf->sample_received++;
179
180         if (pc == ESCAPE_CODE) {
181                 cpu_buf->sample_invalid_eip++;
182                 return 0;
183         }
184
185         if (nr_available_slots(cpu_buf) < 3) {
186                 cpu_buf->sample_lost_overflow++;
187                 return 0;
188         }
189
190         is_kernel = !!is_kernel;
191
192         task = current;
193
194         /* notice a switch from user->kernel or vice versa */
195         if (cpu_buf->last_is_kernel != is_kernel) {
196                 cpu_buf->last_is_kernel = is_kernel;
197                 add_code(cpu_buf, is_kernel);
198         }
199
200         /* notice a task switch */
201         if (cpu_buf->last_task != task) {
202                 cpu_buf->last_task = task;
203                 add_code(cpu_buf, (unsigned long)task);
204         }
205  
206         add_sample(cpu_buf, pc, event);
207         return 1;
208 }
209
210 static int oprofile_begin_trace(struct oprofile_cpu_buffer * cpu_buf)
211 {
212         if (nr_available_slots(cpu_buf) < 4) {
213                 cpu_buf->sample_lost_overflow++;
214                 return 0;
215         }
216
217         add_code(cpu_buf, CPU_TRACE_BEGIN);
218         cpu_buf->tracing = 1;
219         return 1;
220 }
221
222 static void oprofile_end_trace(struct oprofile_cpu_buffer * cpu_buf)
223 {
224         cpu_buf->tracing = 0;
225 }
226
227 void oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
228                                 unsigned long event, int is_kernel)
229 {
230         struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()];
231
232         if (!backtrace_depth) {
233                 log_sample(cpu_buf, pc, is_kernel, event);
234                 return;
235         }
236
237         if (!oprofile_begin_trace(cpu_buf))
238                 return;
239
240         /* if log_sample() fail we can't backtrace since we lost the source
241          * of this event */
242         if (log_sample(cpu_buf, pc, is_kernel, event))
243                 oprofile_ops.backtrace(regs, backtrace_depth);
244         oprofile_end_trace(cpu_buf);
245 }
246
247 void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
248 {
249         int is_kernel = !user_mode(regs);
250         unsigned long pc = profile_pc(regs);
251
252         oprofile_add_ext_sample(pc, regs, event, is_kernel);
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 void oprofile_add_trace(unsigned long pc)
262 {
263         struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()];
264
265         if (!cpu_buf->tracing)
266                 return;
267
268         if (nr_available_slots(cpu_buf) < 1) {
269                 cpu_buf->tracing = 0;
270                 cpu_buf->sample_lost_overflow++;
271                 return;
272         }
273
274         /* broken frame can give an eip with the same value as an escape code,
275          * abort the trace if we get it */
276         if (pc == ESCAPE_CODE) {
277                 cpu_buf->tracing = 0;
278                 cpu_buf->backtrace_aborted++;
279                 return;
280         }
281
282         add_sample(cpu_buf, pc, 0);
283 }
284
285 /*
286  * This serves to avoid cpu buffer overflow, and makes sure
287  * the task mortuary progresses
288  *
289  * By using schedule_delayed_work_on and then schedule_delayed_work
290  * we guarantee this will stay on the correct cpu
291  */
292 static void wq_sync_buffer(struct work_struct *work)
293 {
294         struct oprofile_cpu_buffer * b =
295                 container_of(work, struct oprofile_cpu_buffer, work.work);
296         if (b->cpu != smp_processor_id()) {
297                 printk("WQ on CPU%d, prefer CPU%d\n",
298                        smp_processor_id(), b->cpu);
299         }
300         sync_buffer(b->cpu);
301
302         /* don't re-add the work if we're shutting down */
303         if (work_enabled)
304                 schedule_delayed_work(&b->work, DEFAULT_TIMER_EXPIRE);
305 }