a83c3db7d18fb81a1cd58347ea22ce12a8f9b29c
[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->cpu = i;
68                 INIT_DELAYED_WORK(&b->work, wq_sync_buffer);
69         }
70         return 0;
71
72 fail:
73         free_cpu_buffers();
74         return -ENOMEM;
75 }
76
77 void start_cpu_work(void)
78 {
79         int i;
80
81         work_enabled = 1;
82
83         for_each_online_cpu(i) {
84                 struct oprofile_cpu_buffer * b = &cpu_buffer[i];
85
86                 /*
87                  * Spread the work by 1 jiffy per cpu so they dont all
88                  * fire at once.
89                  */
90                 schedule_delayed_work_on(i, &b->work, DEFAULT_TIMER_EXPIRE + i);
91         }
92 }
93
94 void end_cpu_work(void)
95 {
96         int i;
97
98         work_enabled = 0;
99
100         for_each_online_cpu(i) {
101                 struct oprofile_cpu_buffer * b = &cpu_buffer[i];
102
103                 cancel_delayed_work(&b->work);
104         }
105
106         flush_scheduled_work();
107 }
108
109 /* Resets the cpu buffer to a sane state. */
110 void cpu_buffer_reset(struct oprofile_cpu_buffer * cpu_buf)
111 {
112         /* reset these to invalid values; the next sample
113          * collected will populate the buffer with proper
114          * values to initialize the buffer
115          */
116         cpu_buf->last_is_kernel = -1;
117         cpu_buf->last_task = NULL;
118 }
119
120 /* compute number of available slots in cpu_buffer queue */
121 static unsigned long nr_available_slots(struct oprofile_cpu_buffer const * b)
122 {
123         unsigned long head = b->head_pos;
124         unsigned long tail = b->tail_pos;
125
126         if (tail > head)
127                 return (tail - head) - 1;
128
129         return tail + (b->buffer_size - head) - 1;
130 }
131
132 static void increment_head(struct oprofile_cpu_buffer * b)
133 {
134         unsigned long new_head = b->head_pos + 1;
135
136         /* Ensure anything written to the slot before we
137          * increment is visible */
138         wmb();
139
140         if (new_head < b->buffer_size)
141                 b->head_pos = new_head;
142         else
143                 b->head_pos = 0;
144 }
145
146 static inline void
147 add_sample(struct oprofile_cpu_buffer * cpu_buf,
148            unsigned long pc, unsigned long event)
149 {
150         struct op_sample * entry = &cpu_buf->buffer[cpu_buf->head_pos];
151         entry->eip = pc;
152         entry->event = event;
153         increment_head(cpu_buf);
154 }
155
156 static inline void
157 add_code(struct oprofile_cpu_buffer * buffer, unsigned long value)
158 {
159         add_sample(buffer, ESCAPE_CODE, value);
160 }
161
162 /* This must be safe from any context. It's safe writing here
163  * because of the head/tail separation of the writer and reader
164  * of the CPU buffer.
165  *
166  * is_kernel is needed because on some architectures you cannot
167  * tell if you are in kernel or user space simply by looking at
168  * pc. We tag this in the buffer by generating kernel enter/exit
169  * events whenever is_kernel changes
170  */
171 static int log_sample(struct oprofile_cpu_buffer * cpu_buf, unsigned long pc,
172                       int is_kernel, unsigned long event)
173 {
174         struct task_struct * task;
175
176         cpu_buf->sample_received++;
177
178         if (nr_available_slots(cpu_buf) < 3) {
179                 cpu_buf->sample_lost_overflow++;
180                 return 0;
181         }
182
183         is_kernel = !!is_kernel;
184
185         task = current;
186
187         /* notice a switch from user->kernel or vice versa */
188         if (cpu_buf->last_is_kernel != is_kernel) {
189                 cpu_buf->last_is_kernel = is_kernel;
190                 add_code(cpu_buf, is_kernel);
191         }
192
193         /* notice a task switch */
194         if (cpu_buf->last_task != task) {
195                 cpu_buf->last_task = task;
196                 add_code(cpu_buf, (unsigned long)task);
197         }
198  
199         add_sample(cpu_buf, pc, event);
200         return 1;
201 }
202
203 static int oprofile_begin_trace(struct oprofile_cpu_buffer * cpu_buf)
204 {
205         if (nr_available_slots(cpu_buf) < 4) {
206                 cpu_buf->sample_lost_overflow++;
207                 return 0;
208         }
209
210         add_code(cpu_buf, CPU_TRACE_BEGIN);
211         cpu_buf->tracing = 1;
212         return 1;
213 }
214
215 static void oprofile_end_trace(struct oprofile_cpu_buffer * cpu_buf)
216 {
217         cpu_buf->tracing = 0;
218 }
219
220 void oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
221                                 unsigned long event, int is_kernel)
222 {
223         struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()];
224
225         if (!backtrace_depth) {
226                 log_sample(cpu_buf, pc, is_kernel, event);
227                 return;
228         }
229
230         if (!oprofile_begin_trace(cpu_buf))
231                 return;
232
233         /* if log_sample() fail we can't backtrace since we lost the source
234          * of this event */
235         if (log_sample(cpu_buf, pc, is_kernel, event))
236                 oprofile_ops.backtrace(regs, backtrace_depth);
237         oprofile_end_trace(cpu_buf);
238 }
239
240 void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
241 {
242         int is_kernel = !user_mode(regs);
243         unsigned long pc = profile_pc(regs);
244
245         oprofile_add_ext_sample(pc, regs, event, is_kernel);
246 }
247
248 void oprofile_add_pc(unsigned long pc, int is_kernel, unsigned long event)
249 {
250         struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()];
251         log_sample(cpu_buf, pc, is_kernel, event);
252 }
253
254 void oprofile_add_trace(unsigned long pc)
255 {
256         struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()];
257
258         if (!cpu_buf->tracing)
259                 return;
260
261         if (nr_available_slots(cpu_buf) < 1) {
262                 cpu_buf->tracing = 0;
263                 cpu_buf->sample_lost_overflow++;
264                 return;
265         }
266
267         /* broken frame can give an eip with the same value as an escape code,
268          * abort the trace if we get it */
269         if (pc == ESCAPE_CODE) {
270                 cpu_buf->tracing = 0;
271                 cpu_buf->backtrace_aborted++;
272                 return;
273         }
274
275         add_sample(cpu_buf, pc, 0);
276 }
277
278 /*
279  * This serves to avoid cpu buffer overflow, and makes sure
280  * the task mortuary progresses
281  *
282  * By using schedule_delayed_work_on and then schedule_delayed_work
283  * we guarantee this will stay on the correct cpu
284  */
285 static void wq_sync_buffer(struct work_struct *work)
286 {
287         struct oprofile_cpu_buffer * b =
288                 container_of(work, struct oprofile_cpu_buffer, work.work);
289         if (b->cpu != smp_processor_id()) {
290                 printk("WQ on CPU%d, prefer CPU%d\n",
291                        smp_processor_id(), b->cpu);
292         }
293         sync_buffer(b->cpu);
294
295         /* don't re-add the work if we're shutting down */
296         if (work_enabled)
297                 schedule_delayed_work(&b->work, DEFAULT_TIMER_EXPIRE);
298 }