drivers/oprofile/cpu_buffer.c

   1 /**
   2  * @file cpu_buffer.c
   3  *
   4  * @remark Copyright 2002-2009 OProfile authors
   5  * @remark Read the file COPYING
   6  *
   7  * @author John Levon <levon@movementarian.org>
   8  * @author Barry Kasindorf <barry.kasindorf@amd.com>
   9  * @author Robert Richter <robert.richter@amd.com>
  10  *
  11  * Each CPU has a local buffer that stores PC value/event
  12  * pairs. We also log context switches when we notice them.
  13  * Eventually each CPU's buffer is processed into the global
  14  * event buffer by sync_buffer().
  15  *
  16  * We use a local buffer for two reasons: an NMI or similar
  17  * interrupt cannot synchronise, and high sampling rates
  18  * would lead to catastrophic global synchronisation if
  19  * a global buffer was used.
  20  */
  21
  22 #include <linux/sched.h>
  23 #include <linux/oprofile.h>
  24 #include <linux/vmalloc.h>
  25 #include <linux/errno.h>
  26
  27 #include "event_buffer.h"
  28 #include "cpu_buffer.h"
  29 #include "buffer_sync.h"
  30 #include "oprof.h"
  31
  32 #define OP_BUFFER_FLAGS 0
  33
  34 /*
  35  * Read and write access is using spin locking. Thus, writing to the
  36  * buffer by NMI handler (x86) could occur also during critical
  37  * sections when reading the buffer. To avoid this, there are 2
  38  * buffers for independent read and write access. Read access is in
  39  * process context only, write access only in the NMI handler. If the
  40  * read buffer runs empty, both buffers are swapped atomically. There
  41  * is potentially a small window during swapping where the buffers are
  42  * disabled and samples could be lost.
  43  *
  44  * Using 2 buffers is a little bit overhead, but the solution is clear
  45  * and does not require changes in the ring buffer implementation. It
  46  * can be changed to a single buffer solution when the ring buffer
  47  * access is implemented as non-locking atomic code.
  48  */
  49 static struct ring_buffer *op_ring_buffer_read;
  50 static struct ring_buffer *op_ring_buffer_write;
  51 DEFINE_PER_CPU(struct oprofile_cpu_buffer, cpu_buffer);
  52
  53 static void wq_sync_buffer(struct work_struct *work);
  54
  55 #define DEFAULT_TIMER_EXPIRE (HZ / 10)
  56 static int work_enabled;
  57
  58 unsigned long oprofile_get_cpu_buffer_size(void)
  59 {
  60         return oprofile_cpu_buffer_size;
  61 }
  62
  63 void oprofile_cpu_buffer_inc_smpl_lost(void)
  64 {
  65         struct oprofile_cpu_buffer *cpu_buf
  66                 = &__get_cpu_var(cpu_buffer);
  67
  68         cpu_buf->sample_lost_overflow++;
  69 }
  70
  71 void free_cpu_buffers(void)
  72 {
  73         if (op_ring_buffer_read)
  74                 ring_buffer_free(op_ring_buffer_read);
  75         op_ring_buffer_read = NULL;
  76         if (op_ring_buffer_write)
  77                 ring_buffer_free(op_ring_buffer_write);
  78         op_ring_buffer_write = NULL;
  79 }
  80
  81 int alloc_cpu_buffers(void)
  82 {
  83         int i;
  84
  85         unsigned long buffer_size = oprofile_cpu_buffer_size;
  86
  87         op_ring_buffer_read = ring_buffer_alloc(buffer_size, OP_BUFFER_FLAGS);
  88         if (!op_ring_buffer_read)
  89                 goto fail;
  90         op_ring_buffer_write = ring_buffer_alloc(buffer_size, OP_BUFFER_FLAGS);
  91         if (!op_ring_buffer_write)
  92                 goto fail;
  93
  94         for_each_possible_cpu(i) {
  95                 struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
  96
  97                 b->last_task = NULL;
  98                 b->last_is_kernel = -1;
  99                 b->tracing = 0;
 100                 b->buffer_size = buffer_size;
 101                 b->sample_received = 0;
 102                 b->sample_lost_overflow = 0;
 103                 b->backtrace_aborted = 0;
 104                 b->sample_invalid_eip = 0;
 105                 b->cpu = i;
 106                 INIT_DELAYED_WORK(&b->work, wq_sync_buffer);
 107         }
 108         return 0;
 109
 110 fail:
 111         free_cpu_buffers();
 112         return -ENOMEM;
 113 }
 114
 115 void start_cpu_work(void)
 116 {
 117         int i;
 118
 119         work_enabled = 1;
 120
 121         for_each_online_cpu(i) {
 122                 struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
 123
 124                 /*
 125                  * Spread the work by 1 jiffy per cpu so they dont all
 126                  * fire at once.
 127                  */
 128                 schedule_delayed_work_on(i, &b->work, DEFAULT_TIMER_EXPIRE + i);
 129         }
 130 }
 131
 132 void end_cpu_work(void)
 133 {
 134         int i;
 135
 136         work_enabled = 0;
 137
 138         for_each_online_cpu(i) {
 139                 struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
 140
 141                 cancel_delayed_work(&b->work);
 142         }
 143
 144         flush_scheduled_work();
 145 }
 146
 147 /*
 148  * This function prepares the cpu buffer to write a sample.
 149  *
 150  * Struct op_entry is used during operations on the ring buffer while
 151  * struct op_sample contains the data that is stored in the ring
 152  * buffer. Struct entry can be uninitialized. The function reserves a
 153  * data array that is specified by size. Use
 154  * op_cpu_buffer_write_commit() after preparing the sample. In case of
 155  * errors a null pointer is returned, otherwise the pointer to the
 156  * sample.
 157  *
 158  */
 159 struct op_sample
 160 *op_cpu_buffer_write_reserve(struct op_entry *entry, unsigned long size)
 161 {
 162         entry->event = ring_buffer_lock_reserve
 163                 (op_ring_buffer_write, sizeof(struct op_sample) +
 164                  size * sizeof(entry->sample->data[0]), &entry->irq_flags);
 165         if (entry->event)
 166                 entry->sample = ring_buffer_event_data(entry->event);
 167         else
 168                 entry->sample = NULL;
 169
 170         if (!entry->sample)
 171                 return NULL;
 172
 173         entry->size = size;
 174         entry->data = entry->sample->data;
 175
 176         return entry->sample;
 177 }
 178
 179 int op_cpu_buffer_write_commit(struct op_entry *entry)
 180 {
 181         return ring_buffer_unlock_commit(op_ring_buffer_write, entry->event,
 182                                          entry->irq_flags);
 183 }
 184
 185 struct op_sample *op_cpu_buffer_read_entry(struct op_entry *entry, int cpu)
 186 {
 187         struct ring_buffer_event *e;
 188         e = ring_buffer_consume(op_ring_buffer_read, cpu, NULL);
 189         if (e)
 190                 goto event;
 191         if (ring_buffer_swap_cpu(op_ring_buffer_read,
 192                                  op_ring_buffer_write,
 193                                  cpu))
 194                 return NULL;
 195         e = ring_buffer_consume(op_ring_buffer_read, cpu, NULL);
 196         if (e)
 197                 goto event;
 198         return NULL;
 199
 200 event:
 201         entry->event = e;
 202         entry->sample = ring_buffer_event_data(e);
 203         entry->size = (ring_buffer_event_length(e) - sizeof(struct op_sample))
 204                 / sizeof(entry->sample->data[0]);
 205         entry->data = entry->sample->data;
 206         return entry->sample;
 207 }
 208
 209 unsigned long op_cpu_buffer_entries(int cpu)
 210 {
 211         return ring_buffer_entries_cpu(op_ring_buffer_read, cpu)
 212                 + ring_buffer_entries_cpu(op_ring_buffer_write, cpu);
 213 }
 214
 215 static int
 216 op_add_code(struct oprofile_cpu_buffer *cpu_buf, unsigned long backtrace,
 217             int is_kernel, struct task_struct *task)
 218 {
 219         struct op_entry entry;
 220         struct op_sample *sample;
 221         unsigned long flags;
 222         int size;
 223
 224         flags = 0;
 225
 226         if (backtrace)
 227                 flags |= TRACE_BEGIN;
 228
 229         /* notice a switch from user->kernel or vice versa */
 230         is_kernel = !!is_kernel;
 231         if (cpu_buf->last_is_kernel != is_kernel) {
 232                 cpu_buf->last_is_kernel = is_kernel;
 233                 flags |= KERNEL_CTX_SWITCH;
 234                 if (is_kernel)
 235                         flags |= IS_KERNEL;
 236         }
 237
 238         /* notice a task switch */
 239         if (cpu_buf->last_task != task) {
 240                 cpu_buf->last_task = task;
 241                 flags |= USER_CTX_SWITCH;
 242         }
 243
 244         if (!flags)
 245                 /* nothing to do */
 246                 return 0;
 247
 248         if (flags & USER_CTX_SWITCH)
 249                 size = 1;
 250         else
 251                 size = 0;
 252
 253         sample = op_cpu_buffer_write_reserve(&entry, size);
 254         if (!sample)
 255                 return -ENOMEM;
 256
 257         sample->eip = ESCAPE_CODE;
 258         sample->event = flags;
 259
 260         if (size)
 261                 op_cpu_buffer_add_data(&entry, (unsigned long)task);
 262
 263         op_cpu_buffer_write_commit(&entry);
 264
 265         return 0;
 266 }
 267
 268 static inline int
 269 op_add_sample(struct oprofile_cpu_buffer *cpu_buf,
 270               unsigned long pc, unsigned long event)
 271 {
 272         struct op_entry entry;
 273         struct op_sample *sample;
 274
 275         sample = op_cpu_buffer_write_reserve(&entry, 0);
 276         if (!sample)
 277                 return -ENOMEM;
 278
 279         sample->eip = pc;
 280         sample->event = event;
 281
 282         return op_cpu_buffer_write_commit(&entry);
 283 }
 284
 285 /*
 286  * This must be safe from any context.
 287  *
 288  * is_kernel is needed because on some architectures you cannot
 289  * tell if you are in kernel or user space simply by looking at
 290  * pc. We tag this in the buffer by generating kernel enter/exit
 291  * events whenever is_kernel changes
 292  */
 293 static int
 294 log_sample(struct oprofile_cpu_buffer *cpu_buf, unsigned long pc,
 295            unsigned long backtrace, int is_kernel, unsigned long event)
 296 {
 297         cpu_buf->sample_received++;
 298
 299         if (pc == ESCAPE_CODE) {
 300                 cpu_buf->sample_invalid_eip++;
 301                 return 0;
 302         }
 303
 304         if (op_add_code(cpu_buf, backtrace, is_kernel, current))
 305                 goto fail;
 306
 307         if (op_add_sample(cpu_buf, pc, event))
 308                 goto fail;
 309
 310         return 1;
 311
 312 fail:
 313         cpu_buf->sample_lost_overflow++;
 314         return 0;
 315 }
 316
 317 static inline void oprofile_begin_trace(struct oprofile_cpu_buffer *cpu_buf)
 318 {
 319         cpu_buf->tracing = 1;
 320 }
 321
 322 static inline void oprofile_end_trace(struct oprofile_cpu_buffer *cpu_buf)
 323 {
 324         cpu_buf->tracing = 0;
 325 }
 326
 327 static inline void
 328 __oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
 329                           unsigned long event, int is_kernel)
 330 {
 331         struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
 332         unsigned long backtrace = oprofile_backtrace_depth;
 333
 334         /*
 335          * if log_sample() fail we can't backtrace since we lost the
 336          * source of this event
 337          */
 338         if (!log_sample(cpu_buf, pc, backtrace, is_kernel, event))
 339                 /* failed */
 340                 return;
 341
 342         if (!backtrace)
 343                 return;
 344
 345         oprofile_begin_trace(cpu_buf);
 346         oprofile_ops.backtrace(regs, backtrace);
 347         oprofile_end_trace(cpu_buf);
 348 }
 349
 350 void oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
 351                              unsigned long event, int is_kernel)
 352 {
 353         __oprofile_add_ext_sample(pc, regs, event, is_kernel);
 354 }
 355
 356 void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
 357 {
 358         int is_kernel = !user_mode(regs);
 359         unsigned long pc = profile_pc(regs);
 360
 361         __oprofile_add_ext_sample(pc, regs, event, is_kernel);
 362 }
 363
 364 /*
 365  * Add samples with data to the ring buffer.
 366  *
 367  * Use oprofile_add_data(&entry, val) to add data and
 368  * oprofile_write_commit(&entry) to commit the sample.
 369  */
 370 void
 371 oprofile_write_reserve(struct op_entry *entry, struct pt_regs * const regs,
 372                        unsigned long pc, int code, int size)
 373 {
 374         struct op_sample *sample;
 375         int is_kernel = !user_mode(regs);
 376         struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
 377
 378         cpu_buf->sample_received++;
 379
 380         /* no backtraces for samples with data */
 381         if (op_add_code(cpu_buf, 0, is_kernel, current))
 382                 goto fail;
 383
 384         sample = op_cpu_buffer_write_reserve(entry, size + 2);
 385         if (!sample)
 386                 goto fail;
 387         sample->eip = ESCAPE_CODE;
 388         sample->event = 0;              /* no flags */
 389
 390         op_cpu_buffer_add_data(entry, code);
 391         op_cpu_buffer_add_data(entry, pc);
 392
 393         return;
 394
 395 fail:
 396         entry->event = NULL;
 397         cpu_buf->sample_lost_overflow++;
 398 }
 399
 400 int oprofile_add_data(struct op_entry *entry, unsigned long val)
 401 {
 402         if (!entry->event)
 403                 return 0;
 404         return op_cpu_buffer_add_data(entry, val);
 405 }
 406
 407 int oprofile_write_commit(struct op_entry *entry)
 408 {
 409         if (!entry->event)
 410                 return -EINVAL;
 411         return op_cpu_buffer_write_commit(entry);
 412 }
 413
 414 void oprofile_add_pc(unsigned long pc, int is_kernel, unsigned long event)
 415 {
 416         struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
 417         log_sample(cpu_buf, pc, 0, is_kernel, event);
 418 }
 419
 420 void oprofile_add_trace(unsigned long pc)
 421 {
 422         struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
 423
 424         if (!cpu_buf->tracing)
 425                 return;
 426
 427         /*
 428          * broken frame can give an eip with the same value as an
 429          * escape code, abort the trace if we get it
 430          */
 431         if (pc == ESCAPE_CODE)
 432                 goto fail;
 433
 434         if (op_add_sample(cpu_buf, pc, 0))
 435                 goto fail;
 436
 437         return;
 438 fail:
 439         cpu_buf->tracing = 0;
 440         cpu_buf->backtrace_aborted++;
 441         return;
 442 }
 443
 444 /*
 445  * This serves to avoid cpu buffer overflow, and makes sure
 446  * the task mortuary progresses
 447  *
 448  * By using schedule_delayed_work_on and then schedule_delayed_work
 449  * we guarantee this will stay on the correct cpu
 450  */
 451 static void wq_sync_buffer(struct work_struct *work)
 452 {
 453         struct oprofile_cpu_buffer *b =
 454                 container_of(work, struct oprofile_cpu_buffer, work.work);
 455         if (b->cpu != smp_processor_id()) {
 456                 printk(KERN_DEBUG "WQ on CPU%d, prefer CPU%d\n",
 457                        smp_processor_id(), b->cpu);
 458
 459                 if (!cpu_online(b->cpu)) {
 460                         cancel_delayed_work(&b->work);
 461                         return;
 462                 }
 463         }
 464         sync_buffer(b->cpu);
 465
 466         /* don't re-add the work if we're shutting down */
 467         if (work_enabled)
 468                 schedule_delayed_work(&b->work, DEFAULT_TIMER_EXPIRE);
 469 }