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  * @author Barry Kasindorf <barry.kasindorf@amd.com>
   9  *
  10  * Each CPU has a local buffer that stores PC value/event
  11  * pairs. We also log context switches when we notice them.
  12  * Eventually each CPU's buffer is processed into the global
  13  * event buffer by sync_buffer().
  14  *
  15  * We use a local buffer for two reasons: an NMI or similar
  16  * interrupt cannot synchronise, and high sampling rates
  17  * would lead to catastrophic global synchronisation if
  18  * a global buffer was used.
  19  */
  20
  21 #include <linux/sched.h>
  22 #include <linux/oprofile.h>
  23 #include <linux/vmalloc.h>
  24 #include <linux/errno.h>
  25
  26 #include "event_buffer.h"
  27 #include "cpu_buffer.h"
  28 #include "buffer_sync.h"
  29 #include "oprof.h"
  30
  31 #define OP_BUFFER_FLAGS 0
  32
  33 /*
  34  * Read and write access is using spin locking. Thus, writing to the
  35  * buffer by NMI handler (x86) could occur also during critical
  36  * sections when reading the buffer. To avoid this, there are 2
  37  * buffers for independent read and write access. Read access is in
  38  * process context only, write access only in the NMI handler. If the
  39  * read buffer runs empty, both buffers are swapped atomically. There
  40  * is potentially a small window during swapping where the buffers are
  41  * disabled and samples could be lost.
  42  *
  43  * Using 2 buffers is a little bit overhead, but the solution is clear
  44  * and does not require changes in the ring buffer implementation. It
  45  * can be changed to a single buffer solution when the ring buffer
  46  * access is implemented as non-locking atomic code.
  47  */
  48 struct ring_buffer *op_ring_buffer_read;
  49 struct ring_buffer *op_ring_buffer_write;
  50 DEFINE_PER_CPU(struct oprofile_cpu_buffer, cpu_buffer);
  51
  52 static void wq_sync_buffer(struct work_struct *work);
  53
  54 #define DEFAULT_TIMER_EXPIRE (HZ / 10)
  55 static int work_enabled;
  56
  57 void free_cpu_buffers(void)
  58 {
  59         if (op_ring_buffer_read)
  60                 ring_buffer_free(op_ring_buffer_read);
  61         op_ring_buffer_read = NULL;
  62         if (op_ring_buffer_write)
  63                 ring_buffer_free(op_ring_buffer_write);
  64         op_ring_buffer_write = NULL;
  65 }
  66
  67 unsigned long oprofile_get_cpu_buffer_size(void)
  68 {
  69         return fs_cpu_buffer_size;
  70 }
  71
  72 void oprofile_cpu_buffer_inc_smpl_lost(void)
  73 {
  74         struct oprofile_cpu_buffer *cpu_buf
  75                 = &__get_cpu_var(cpu_buffer);
  76
  77         cpu_buf->sample_lost_overflow++;
  78 }
  79
  80 int alloc_cpu_buffers(void)
  81 {
  82         int i;
  83
  84         unsigned long buffer_size = fs_cpu_buffer_size;
  85
  86         op_ring_buffer_read = ring_buffer_alloc(buffer_size, OP_BUFFER_FLAGS);
  87         if (!op_ring_buffer_read)
  88                 goto fail;
  89         op_ring_buffer_write = ring_buffer_alloc(buffer_size, OP_BUFFER_FLAGS);
  90         if (!op_ring_buffer_write)
  91                 goto fail;
  92
  93         for_each_possible_cpu(i) {
  94                 struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
  95
  96                 b->last_task = NULL;
  97                 b->last_is_kernel = -1;
  98                 b->tracing = 0;
  99                 b->buffer_size = buffer_size;
 100                 b->tail_pos = 0;
 101                 b->head_pos = 0;
 102                 b->sample_received = 0;
 103                 b->sample_lost_overflow = 0;
 104                 b->backtrace_aborted = 0;
 105                 b->sample_invalid_eip = 0;
 106                 b->cpu = i;
 107                 INIT_DELAYED_WORK(&b->work, wq_sync_buffer);
 108         }
 109         return 0;
 110
 111 fail:
 112         free_cpu_buffers();
 113         return -ENOMEM;
 114 }
 115
 116 void start_cpu_work(void)
 117 {
 118         int i;
 119
 120         work_enabled = 1;
 121
 122         for_each_online_cpu(i) {
 123                 struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
 124
 125                 /*
 126                  * Spread the work by 1 jiffy per cpu so they dont all
 127                  * fire at once.
 128                  */
 129                 schedule_delayed_work_on(i, &b->work, DEFAULT_TIMER_EXPIRE + i);
 130         }
 131 }
 132
 133 void end_cpu_work(void)
 134 {
 135         int i;
 136
 137         work_enabled = 0;
 138
 139         for_each_online_cpu(i) {
 140                 struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
 141
 142                 cancel_delayed_work(&b->work);
 143         }
 144
 145         flush_scheduled_work();
 146 }
 147
 148 static inline int
 149 add_sample(struct oprofile_cpu_buffer *cpu_buf,
 150            unsigned long pc, unsigned long event)
 151 {
 152         struct op_entry entry;
 153         int ret;
 154
 155         ret = cpu_buffer_write_entry(&entry);
 156         if (ret)
 157                 return ret;
 158
 159         entry.sample->eip = pc;
 160         entry.sample->event = event;
 161
 162         ret = cpu_buffer_write_commit(&entry);
 163         if (ret)
 164                 return ret;
 165
 166         return 0;
 167 }
 168
 169 static inline int
 170 add_code(struct oprofile_cpu_buffer *buffer, unsigned long value)
 171 {
 172         return add_sample(buffer, ESCAPE_CODE, value);
 173 }
 174
 175 /* This must be safe from any context. It's safe writing here
 176  * because of the head/tail separation of the writer and reader
 177  * of the CPU buffer.
 178  *
 179  * is_kernel is needed because on some architectures you cannot
 180  * tell if you are in kernel or user space simply by looking at
 181  * pc. We tag this in the buffer by generating kernel enter/exit
 182  * events whenever is_kernel changes
 183  */
 184 static int log_sample(struct oprofile_cpu_buffer *cpu_buf, unsigned long pc,
 185                       int is_kernel, unsigned long event)
 186 {
 187         struct task_struct *task;
 188
 189         cpu_buf->sample_received++;
 190
 191         if (pc == ESCAPE_CODE) {
 192                 cpu_buf->sample_invalid_eip++;
 193                 return 0;
 194         }
 195
 196         is_kernel = !!is_kernel;
 197
 198         task = current;
 199
 200         /* notice a switch from user->kernel or vice versa */
 201         if (cpu_buf->last_is_kernel != is_kernel) {
 202                 cpu_buf->last_is_kernel = is_kernel;
 203                 if (add_code(cpu_buf, is_kernel))
 204                         goto fail;
 205         }
 206
 207         /* notice a task switch */
 208         if (cpu_buf->last_task != task) {
 209                 cpu_buf->last_task = task;
 210                 if (add_code(cpu_buf, (unsigned long)task))
 211                         goto fail;
 212         }
 213
 214         if (add_sample(cpu_buf, pc, event))
 215                 goto fail;
 216
 217         return 1;
 218
 219 fail:
 220         cpu_buf->sample_lost_overflow++;
 221         return 0;
 222 }
 223
 224 static int oprofile_begin_trace(struct oprofile_cpu_buffer *cpu_buf)
 225 {
 226         add_code(cpu_buf, CPU_TRACE_BEGIN);
 227         cpu_buf->tracing = 1;
 228         return 1;
 229 }
 230
 231 static void oprofile_end_trace(struct oprofile_cpu_buffer *cpu_buf)
 232 {
 233         cpu_buf->tracing = 0;
 234 }
 235
 236 void oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
 237                                 unsigned long event, int is_kernel)
 238 {
 239         struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
 240
 241         if (!backtrace_depth) {
 242                 log_sample(cpu_buf, pc, is_kernel, event);
 243                 return;
 244         }
 245
 246         if (!oprofile_begin_trace(cpu_buf))
 247                 return;
 248
 249         /*
 250          * if log_sample() fail we can't backtrace since we lost the
 251          * source of this event
 252          */
 253         if (log_sample(cpu_buf, pc, is_kernel, event))
 254                 oprofile_ops.backtrace(regs, backtrace_depth);
 255         oprofile_end_trace(cpu_buf);
 256 }
 257
 258 void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
 259 {
 260         int is_kernel = !user_mode(regs);
 261         unsigned long pc = profile_pc(regs);
 262
 263         oprofile_add_ext_sample(pc, regs, event, is_kernel);
 264 }
 265
 266 #ifdef CONFIG_OPROFILE_IBS
 267
 268 #define MAX_IBS_SAMPLE_SIZE 14
 269
 270 void oprofile_add_ibs_sample(struct pt_regs * const regs,
 271                              unsigned int * const ibs_sample, int ibs_code)
 272 {
 273         int is_kernel = !user_mode(regs);
 274         struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
 275         struct task_struct *task;
 276         int fail = 0;
 277
 278         cpu_buf->sample_received++;
 279
 280         /* notice a switch from user->kernel or vice versa */
 281         if (cpu_buf->last_is_kernel != is_kernel) {
 282                 if (add_code(cpu_buf, is_kernel))
 283                         goto fail;
 284                 cpu_buf->last_is_kernel = is_kernel;
 285         }
 286
 287         /* notice a task switch */
 288         if (!is_kernel) {
 289                 task = current;
 290                 if (cpu_buf->last_task != task) {
 291                         if (add_code(cpu_buf, (unsigned long)task))
 292                                 goto fail;
 293                         cpu_buf->last_task = task;
 294                 }
 295         }
 296
 297         fail = fail || add_code(cpu_buf, ibs_code);
 298         fail = fail || add_sample(cpu_buf, ibs_sample[0], ibs_sample[1]);
 299         fail = fail || add_sample(cpu_buf, ibs_sample[2], ibs_sample[3]);
 300         fail = fail || add_sample(cpu_buf, ibs_sample[4], ibs_sample[5]);
 301
 302         if (ibs_code == IBS_OP_BEGIN) {
 303                 fail = fail || add_sample(cpu_buf, ibs_sample[6], ibs_sample[7]);
 304                 fail = fail || add_sample(cpu_buf, ibs_sample[8], ibs_sample[9]);
 305                 fail = fail || add_sample(cpu_buf, ibs_sample[10], ibs_sample[11]);
 306         }
 307
 308         if (fail)
 309                 goto fail;
 310
 311         if (backtrace_depth)
 312                 oprofile_ops.backtrace(regs, backtrace_depth);
 313
 314         return;
 315
 316 fail:
 317         cpu_buf->sample_lost_overflow++;
 318         return;
 319 }
 320
 321 #endif
 322
 323 void oprofile_add_pc(unsigned long pc, int is_kernel, unsigned long event)
 324 {
 325         struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
 326         log_sample(cpu_buf, pc, is_kernel, event);
 327 }
 328
 329 void oprofile_add_trace(unsigned long pc)
 330 {
 331         struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
 332
 333         if (!cpu_buf->tracing)
 334                 return;
 335
 336         /*
 337          * broken frame can give an eip with the same value as an
 338          * escape code, abort the trace if we get it
 339          */
 340         if (pc == ESCAPE_CODE)
 341                 goto fail;
 342
 343         if (add_sample(cpu_buf, pc, 0))
 344                 goto fail;
 345
 346         return;
 347 fail:
 348         cpu_buf->tracing = 0;
 349         cpu_buf->backtrace_aborted++;
 350         return;
 351 }
 352
 353 /*
 354  * This serves to avoid cpu buffer overflow, and makes sure
 355  * the task mortuary progresses
 356  *
 357  * By using schedule_delayed_work_on and then schedule_delayed_work
 358  * we guarantee this will stay on the correct cpu
 359  */
 360 static void wq_sync_buffer(struct work_struct *work)
 361 {
 362         struct oprofile_cpu_buffer *b =
 363                 container_of(work, struct oprofile_cpu_buffer, work.work);
 364         if (b->cpu != smp_processor_id()) {
 365                 printk(KERN_DEBUG "WQ on CPU%d, prefer CPU%d\n",
 366                        smp_processor_id(), b->cpu);
 367
 368                 if (!cpu_online(b->cpu)) {
 369                         cancel_delayed_work(&b->work);
 370                         return;
 371                 }
 372         }
 373         sync_buffer(b->cpu);
 374
 375         /* don't re-add the work if we're shutting down */
 376         if (work_enabled)
 377                 schedule_delayed_work(&b->work, DEFAULT_TIMER_EXPIRE);
 378 }