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 #define RB_EVENT_HDR_SIZE 4
  82
  83 int alloc_cpu_buffers(void)
  84 {
  85         int i;
  86
  87         unsigned long buffer_size = oprofile_cpu_buffer_size;
  88         unsigned long byte_size = buffer_size * (sizeof(struct op_sample) +
  89                                                  RB_EVENT_HDR_SIZE);
  90
  91         op_ring_buffer_read = ring_buffer_alloc(byte_size, OP_BUFFER_FLAGS);
  92         if (!op_ring_buffer_read)
  93                 goto fail;
  94         op_ring_buffer_write = ring_buffer_alloc(byte_size, OP_BUFFER_FLAGS);
  95         if (!op_ring_buffer_write)
  96                 goto fail;
  97
  98         for_each_possible_cpu(i) {
  99                 struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
 100
 101                 b->last_task = NULL;
 102                 b->last_is_kernel = -1;
 103                 b->tracing = 0;
 104                 b->buffer_size = buffer_size;
 105                 b->sample_received = 0;
 106                 b->sample_lost_overflow = 0;
 107                 b->backtrace_aborted = 0;
 108                 b->sample_invalid_eip = 0;
 109                 b->cpu = i;
 110                 INIT_DELAYED_WORK(&b->work, wq_sync_buffer);
 111         }
 112         return 0;
 113
 114 fail:
 115         free_cpu_buffers();
 116         return -ENOMEM;
 117 }
 118
 119 void start_cpu_work(void)
 120 {
 121         int i;
 122
 123         work_enabled = 1;
 124
 125         for_each_online_cpu(i) {
 126                 struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
 127
 128                 /*
 129                  * Spread the work by 1 jiffy per cpu so they dont all
 130                  * fire at once.
 131                  */
 132                 schedule_delayed_work_on(i, &b->work, DEFAULT_TIMER_EXPIRE + i);
 133         }
 134 }
 135
 136 void end_cpu_work(void)
 137 {
 138         int i;
 139
 140         work_enabled = 0;
 141
 142         for_each_online_cpu(i) {
 143                 struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
 144
 145                 cancel_delayed_work(&b->work);
 146         }
 147
 148         flush_scheduled_work();
 149 }
 150
 151 /*
 152  * This function prepares the cpu buffer to write a sample.
 153  *
 154  * Struct op_entry is used during operations on the ring buffer while
 155  * struct op_sample contains the data that is stored in the ring
 156  * buffer. Struct entry can be uninitialized. The function reserves a
 157  * data array that is specified by size. Use
 158  * op_cpu_buffer_write_commit() after preparing the sample. In case of
 159  * errors a null pointer is returned, otherwise the pointer to the
 160  * sample.
 161  *
 162  */
 163 struct op_sample
 164 *op_cpu_buffer_write_reserve(struct op_entry *entry, unsigned long size)
 165 {
 166         entry->event = ring_buffer_lock_reserve
 167                 (op_ring_buffer_write, sizeof(struct op_sample) +
 168                  size * sizeof(entry->sample->data[0]));
 169         if (entry->event)
 170                 entry->sample = ring_buffer_event_data(entry->event);
 171         else
 172                 entry->sample = NULL;
 173
 174         if (!entry->sample)
 175                 return NULL;
 176
 177         entry->size = size;
 178         entry->data = entry->sample->data;
 179
 180         return entry->sample;
 181 }
 182
 183 int op_cpu_buffer_write_commit(struct op_entry *entry)
 184 {
 185         return ring_buffer_unlock_commit(op_ring_buffer_write, entry->event);
 186 }
 187
 188 struct op_sample *op_cpu_buffer_read_entry(struct op_entry *entry, int cpu)
 189 {
 190         struct ring_buffer_event *e;
 191         e = ring_buffer_consume(op_ring_buffer_read, cpu, NULL);
 192         if (e)
 193                 goto event;
 194         if (ring_buffer_swap_cpu(op_ring_buffer_read,
 195                                  op_ring_buffer_write,
 196                                  cpu))
 197                 return NULL;
 198         e = ring_buffer_consume(op_ring_buffer_read, cpu, NULL);
 199         if (e)
 200                 goto event;
 201         return NULL;
 202
 203 event:
 204         entry->event = e;
 205         entry->sample = ring_buffer_event_data(e);
 206         entry->size = (ring_buffer_event_length(e) - sizeof(struct op_sample))
 207                 / sizeof(entry->sample->data[0]);
 208         entry->data = entry->sample->data;
 209         return entry->sample;
 210 }
 211
 212 unsigned long op_cpu_buffer_entries(int cpu)
 213 {
 214         return ring_buffer_entries_cpu(op_ring_buffer_read, cpu)
 215                 + ring_buffer_entries_cpu(op_ring_buffer_write, cpu);
 216 }
 217
 218 static int
 219 op_add_code(struct oprofile_cpu_buffer *cpu_buf, unsigned long backtrace,
 220             int is_kernel, struct task_struct *task)
 221 {
 222         struct op_entry entry;
 223         struct op_sample *sample;
 224         unsigned long flags;
 225         int size;
 226
 227         flags = 0;
 228
 229         if (backtrace)
 230                 flags |= TRACE_BEGIN;
 231
 232         /* notice a switch from user->kernel or vice versa */
 233         is_kernel = !!is_kernel;
 234         if (cpu_buf->last_is_kernel != is_kernel) {
 235                 cpu_buf->last_is_kernel = is_kernel;
 236                 flags |= KERNEL_CTX_SWITCH;
 237                 if (is_kernel)
 238                         flags |= IS_KERNEL;
 239         }
 240
 241         /* notice a task switch */
 242         if (cpu_buf->last_task != task) {
 243                 cpu_buf->last_task = task;
 244                 flags |= USER_CTX_SWITCH;
 245         }
 246
 247         if (!flags)
 248                 /* nothing to do */
 249                 return 0;
 250
 251         if (flags & USER_CTX_SWITCH)
 252                 size = 1;
 253         else
 254                 size = 0;
 255
 256         sample = op_cpu_buffer_write_reserve(&entry, size);
 257         if (!sample)
 258                 return -ENOMEM;
 259
 260         sample->eip = ESCAPE_CODE;
 261         sample->event = flags;
 262
 263         if (size)
 264                 op_cpu_buffer_add_data(&entry, (unsigned long)task);
 265
 266         op_cpu_buffer_write_commit(&entry);
 267
 268         return 0;
 269 }
 270
 271 static inline int
 272 op_add_sample(struct oprofile_cpu_buffer *cpu_buf,
 273               unsigned long pc, unsigned long event)
 274 {
 275         struct op_entry entry;
 276         struct op_sample *sample;
 277
 278         sample = op_cpu_buffer_write_reserve(&entry, 0);
 279         if (!sample)
 280                 return -ENOMEM;
 281
 282         sample->eip = pc;
 283         sample->event = event;
 284
 285         return op_cpu_buffer_write_commit(&entry);
 286 }
 287
 288 /*
 289  * This must be safe from any context.
 290  *
 291  * is_kernel is needed because on some architectures you cannot
 292  * tell if you are in kernel or user space simply by looking at
 293  * pc. We tag this in the buffer by generating kernel enter/exit
 294  * events whenever is_kernel changes
 295  */
 296 static int
 297 log_sample(struct oprofile_cpu_buffer *cpu_buf, unsigned long pc,
 298            unsigned long backtrace, int is_kernel, unsigned long event)
 299 {
 300         cpu_buf->sample_received++;
 301
 302         if (pc == ESCAPE_CODE) {
 303                 cpu_buf->sample_invalid_eip++;
 304                 return 0;
 305         }
 306
 307         if (op_add_code(cpu_buf, backtrace, is_kernel, current))
 308                 goto fail;
 309
 310         if (op_add_sample(cpu_buf, pc, event))
 311                 goto fail;
 312
 313         return 1;
 314
 315 fail:
 316         cpu_buf->sample_lost_overflow++;
 317         return 0;
 318 }
 319
 320 static inline void oprofile_begin_trace(struct oprofile_cpu_buffer *cpu_buf)
 321 {
 322         cpu_buf->tracing = 1;
 323 }
 324
 325 static inline void oprofile_end_trace(struct oprofile_cpu_buffer *cpu_buf)
 326 {
 327         cpu_buf->tracing = 0;
 328 }
 329
 330 static inline void
 331 __oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
 332                           unsigned long event, int is_kernel)
 333 {
 334         struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
 335         unsigned long backtrace = oprofile_backtrace_depth;
 336
 337         /*
 338          * if log_sample() fail we can't backtrace since we lost the
 339          * source of this event
 340          */
 341         if (!log_sample(cpu_buf, pc, backtrace, is_kernel, event))
 342                 /* failed */
 343                 return;
 344
 345         if (!backtrace)
 346                 return;
 347
 348         oprofile_begin_trace(cpu_buf);
 349         oprofile_ops.backtrace(regs, backtrace);
 350         oprofile_end_trace(cpu_buf);
 351 }
 352
 353 void oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
 354                              unsigned long event, int is_kernel)
 355 {
 356         __oprofile_add_ext_sample(pc, regs, event, is_kernel);
 357 }
 358
 359 void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
 360 {
 361         int is_kernel = !user_mode(regs);
 362         unsigned long pc = profile_pc(regs);
 363
 364         __oprofile_add_ext_sample(pc, regs, event, is_kernel);
 365 }
 366
 367 /*
 368  * Add samples with data to the ring buffer.
 369  *
 370  * Use oprofile_add_data(&entry, val) to add data and
 371  * oprofile_write_commit(&entry) to commit the sample.
 372  */
 373 void
 374 oprofile_write_reserve(struct op_entry *entry, struct pt_regs * const regs,
 375                        unsigned long pc, int code, int size)
 376 {
 377         struct op_sample *sample;
 378         int is_kernel = !user_mode(regs);
 379         struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
 380
 381         cpu_buf->sample_received++;
 382
 383         /* no backtraces for samples with data */
 384         if (op_add_code(cpu_buf, 0, is_kernel, current))
 385                 goto fail;
 386
 387         sample = op_cpu_buffer_write_reserve(entry, size + 2);
 388         if (!sample)
 389                 goto fail;
 390         sample->eip = ESCAPE_CODE;
 391         sample->event = 0;              /* no flags */
 392
 393         op_cpu_buffer_add_data(entry, code);
 394         op_cpu_buffer_add_data(entry, pc);
 395
 396         return;
 397
 398 fail:
 399         entry->event = NULL;
 400         cpu_buf->sample_lost_overflow++;
 401 }
 402
 403 int oprofile_add_data(struct op_entry *entry, unsigned long val)
 404 {
 405         if (!entry->event)
 406                 return 0;
 407         return op_cpu_buffer_add_data(entry, val);
 408 }
 409
 410 int oprofile_write_commit(struct op_entry *entry)
 411 {
 412         if (!entry->event)
 413                 return -EINVAL;
 414         return op_cpu_buffer_write_commit(entry);
 415 }
 416
 417 void oprofile_add_pc(unsigned long pc, int is_kernel, unsigned long event)
 418 {
 419         struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
 420         log_sample(cpu_buf, pc, 0, is_kernel, event);
 421 }
 422
 423 void oprofile_add_trace(unsigned long pc)
 424 {
 425         struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
 426
 427         if (!cpu_buf->tracing)
 428                 return;
 429
 430         /*
 431          * broken frame can give an eip with the same value as an
 432          * escape code, abort the trace if we get it
 433          */
 434         if (pc == ESCAPE_CODE)
 435                 goto fail;
 436
 437         if (op_add_sample(cpu_buf, pc, 0))
 438                 goto fail;
 439
 440         return;
 441 fail:
 442         cpu_buf->tracing = 0;
 443         cpu_buf->backtrace_aborted++;
 444         return;
 445 }
 446
 447 /*
 448  * This serves to avoid cpu buffer overflow, and makes sure
 449  * the task mortuary progresses
 450  *
 451  * By using schedule_delayed_work_on and then schedule_delayed_work
 452  * we guarantee this will stay on the correct cpu
 453  */
 454 static void wq_sync_buffer(struct work_struct *work)
 455 {
 456         struct oprofile_cpu_buffer *b =
 457                 container_of(work, struct oprofile_cpu_buffer, work.work);
 458         if (b->cpu != smp_processor_id()) {
 459                 printk(KERN_DEBUG "WQ on CPU%d, prefer CPU%d\n",
 460                        smp_processor_id(), b->cpu);
 461
 462                 if (!cpu_online(b->cpu)) {
 463                         cancel_delayed_work(&b->work);
 464                         return;
 465                 }
 466         }
 467         sync_buffer(b->cpu);
 468
 469         /* don't re-add the work if we're shutting down */
 470         if (work_enabled)
 471                 schedule_delayed_work(&b->work, DEFAULT_TIMER_EXPIRE);
 472 }