kernel/events/ring_buffer.c

   1 /*
   2  * Performance events ring-buffer code:
   3  *
   4  *  Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
   5  *  Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
   6  *  Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
   7  *  Copyright  ©  2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
   8  *
   9  * For licensing details see kernel-base/COPYING
  10  */
  11
  12 #include <linux/perf_event.h>
  13 #include <linux/vmalloc.h>
  14 #include <linux/slab.h>
  15 #include <linux/circ_buf.h>
  16
  17 #include "internal.h"
  18
  19 static void perf_output_wakeup(struct perf_output_handle *handle)
  20 {
  21         atomic_set(&handle->rb->poll, POLL_IN);
  22
  23         handle->event->pending_wakeup = 1;
  24         irq_work_queue(&handle->event->pending);
  25 }
  26
  27 /*
  28  * We need to ensure a later event_id doesn't publish a head when a former
  29  * event isn't done writing. However since we need to deal with NMIs we
  30  * cannot fully serialize things.
  31  *
  32  * We only publish the head (and generate a wakeup) when the outer-most
  33  * event completes.
  34  */
  35 static void perf_output_get_handle(struct perf_output_handle *handle)
  36 {
  37         struct ring_buffer *rb = handle->rb;
  38
  39         preempt_disable();
  40         local_inc(&rb->nest);
  41         handle->wakeup = local_read(&rb->wakeup);
  42 }
  43
  44 static void perf_output_put_handle(struct perf_output_handle *handle)
  45 {
  46         struct ring_buffer *rb = handle->rb;
  47         unsigned long head;
  48
  49 again:
  50         head = local_read(&rb->head);
  51
  52         /*
  53          * IRQ/NMI can happen here, which means we can miss a head update.
  54          */
  55
  56         if (!local_dec_and_test(&rb->nest))
  57                 goto out;
  58
  59         /*
  60          * Since the mmap() consumer (userspace) can run on a different CPU:
  61          *
  62          *   kernel                             user
  63          *
  64          *   READ ->data_tail                   READ ->data_head
  65          *   smp_mb()   (A)                     smp_rmb()       (C)
  66          *   WRITE $data                        READ $data
  67          *   smp_wmb()  (B)                     smp_mb()        (D)
  68          *   STORE ->data_head                  WRITE ->data_tail
  69          *
  70          * Where A pairs with D, and B pairs with C.
  71          *
  72          * I don't think A needs to be a full barrier because we won't in fact
  73          * write data until we see the store from userspace. So we simply don't
  74          * issue the data WRITE until we observe it. Be conservative for now.
  75          *
  76          * OTOH, D needs to be a full barrier since it separates the data READ
  77          * from the tail WRITE.
  78          *
  79          * For B a WMB is sufficient since it separates two WRITEs, and for C
  80          * an RMB is sufficient since it separates two READs.
  81          *
  82          * See perf_output_begin().
  83          */
  84         smp_wmb();
  85         rb->user_page->data_head = head;
  86
  87         /*
  88          * Now check if we missed an update, rely on the (compiler)
  89          * barrier in atomic_dec_and_test() to re-read rb->head.
  90          */
  91         if (unlikely(head != local_read(&rb->head))) {
  92                 local_inc(&rb->nest);
  93                 goto again;
  94         }
  95
  96         if (handle->wakeup != local_read(&rb->wakeup))
  97                 perf_output_wakeup(handle);
  98
  99 out:
 100         preempt_enable();
 101 }
 102
 103 int perf_output_begin(struct perf_output_handle *handle,
 104                       struct perf_event *event, unsigned int size)
 105 {
 106         struct ring_buffer *rb;
 107         unsigned long tail, offset, head;
 108         int have_lost;
 109         struct perf_sample_data sample_data;
 110         struct {
 111                 struct perf_event_header header;
 112                 u64                      id;
 113                 u64                      lost;
 114         } lost_event;
 115
 116         rcu_read_lock();
 117         /*
 118          * For inherited events we send all the output towards the parent.
 119          */
 120         if (event->parent)
 121                 event = event->parent;
 122
 123         rb = rcu_dereference(event->rb);
 124         if (unlikely(!rb))
 125                 goto out;
 126
 127         if (unlikely(!rb->nr_pages))
 128                 goto out;
 129
 130         handle->rb    = rb;
 131         handle->event = event;
 132
 133         have_lost = local_read(&rb->lost);
 134         if (unlikely(have_lost)) {
 135                 lost_event.header.size = sizeof(lost_event);
 136                 perf_event_header__init_id(&lost_event.header, &sample_data,
 137                                            event);
 138                 size += lost_event.header.size;
 139         }
 140
 141         perf_output_get_handle(handle);
 142
 143         do {
 144                 /*
 145                  * Userspace could choose to issue a mb() before updating the
 146                  * tail pointer. So that all reads will be completed before the
 147                  * write is issued.
 148                  *
 149                  * See perf_output_put_handle().
 150                  */
 151                 tail = ACCESS_ONCE(rb->user_page->data_tail);
 152                 smp_mb();
 153                 offset = head = local_read(&rb->head);
 154                 if (!rb->overwrite &&
 155                     unlikely(CIRC_SPACE(head, tail, perf_data_size(rb)) < size))
 156                         goto fail;
 157                 head += size;
 158         } while (local_cmpxchg(&rb->head, offset, head) != offset);
 159
 160         if (unlikely(head - local_read(&rb->wakeup) > rb->watermark))
 161                 local_add(rb->watermark, &rb->wakeup);
 162
 163         handle->page = offset >> (PAGE_SHIFT + page_order(rb));
 164         handle->page &= rb->nr_pages - 1;
 165         handle->size = offset & ((PAGE_SIZE << page_order(rb)) - 1);
 166         handle->addr = rb->data_pages[handle->page];
 167         handle->addr += handle->size;
 168         handle->size = (PAGE_SIZE << page_order(rb)) - handle->size;
 169
 170         if (unlikely(have_lost)) {
 171                 lost_event.header.type = PERF_RECORD_LOST;
 172                 lost_event.header.misc = 0;
 173                 lost_event.id          = event->id;
 174                 lost_event.lost        = local_xchg(&rb->lost, 0);
 175
 176                 perf_output_put(handle, lost_event);
 177                 perf_event__output_id_sample(event, handle, &sample_data);
 178         }
 179
 180         return 0;
 181
 182 fail:
 183         local_inc(&rb->lost);
 184         perf_output_put_handle(handle);
 185 out:
 186         rcu_read_unlock();
 187
 188         return -ENOSPC;
 189 }
 190
 191 unsigned int perf_output_copy(struct perf_output_handle *handle,
 192                       const void *buf, unsigned int len)
 193 {
 194         return __output_copy(handle, buf, len);
 195 }
 196
 197 unsigned int perf_output_skip(struct perf_output_handle *handle,
 198                               unsigned int len)
 199 {
 200         return __output_skip(handle, NULL, len);
 201 }
 202
 203 void perf_output_end(struct perf_output_handle *handle)
 204 {
 205         perf_output_put_handle(handle);
 206         rcu_read_unlock();
 207 }
 208
 209 static void
 210 ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
 211 {
 212         long max_size = perf_data_size(rb);
 213
 214         if (watermark)
 215                 rb->watermark = min(max_size, watermark);
 216
 217         if (!rb->watermark)
 218                 rb->watermark = max_size / 2;
 219
 220         if (flags & RING_BUFFER_WRITABLE)
 221                 rb->overwrite = 0;
 222         else
 223                 rb->overwrite = 1;
 224
 225         atomic_set(&rb->refcount, 1);
 226
 227         INIT_LIST_HEAD(&rb->event_list);
 228         spin_lock_init(&rb->event_lock);
 229 }
 230
 231 #ifndef CONFIG_PERF_USE_VMALLOC
 232
 233 /*
 234  * Back perf_mmap() with regular GFP_KERNEL-0 pages.
 235  */
 236
 237 struct page *
 238 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
 239 {
 240         if (pgoff > rb->nr_pages)
 241                 return NULL;
 242
 243         if (pgoff == 0)
 244                 return virt_to_page(rb->user_page);
 245
 246         return virt_to_page(rb->data_pages[pgoff - 1]);
 247 }
 248
 249 static void *perf_mmap_alloc_page(int cpu)
 250 {
 251         struct page *page;
 252         int node;
 253
 254         node = (cpu == -1) ? cpu : cpu_to_node(cpu);
 255         page = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0);
 256         if (!page)
 257                 return NULL;
 258
 259         return page_address(page);
 260 }
 261
 262 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
 263 {
 264         struct ring_buffer *rb;
 265         unsigned long size;
 266         int i;
 267
 268         size = sizeof(struct ring_buffer);
 269         size += nr_pages * sizeof(void *);
 270
 271         rb = kzalloc(size, GFP_KERNEL);
 272         if (!rb)
 273                 goto fail;
 274
 275         rb->user_page = perf_mmap_alloc_page(cpu);
 276         if (!rb->user_page)
 277                 goto fail_user_page;
 278
 279         for (i = 0; i < nr_pages; i++) {
 280                 rb->data_pages[i] = perf_mmap_alloc_page(cpu);
 281                 if (!rb->data_pages[i])
 282                         goto fail_data_pages;
 283         }
 284
 285         rb->nr_pages = nr_pages;
 286
 287         ring_buffer_init(rb, watermark, flags);
 288
 289         return rb;
 290
 291 fail_data_pages:
 292         for (i--; i >= 0; i--)
 293                 free_page((unsigned long)rb->data_pages[i]);
 294
 295         free_page((unsigned long)rb->user_page);
 296
 297 fail_user_page:
 298         kfree(rb);
 299
 300 fail:
 301         return NULL;
 302 }
 303
 304 static void perf_mmap_free_page(unsigned long addr)
 305 {
 306         struct page *page = virt_to_page((void *)addr);
 307
 308         page->mapping = NULL;
 309         __free_page(page);
 310 }
 311
 312 void rb_free(struct ring_buffer *rb)
 313 {
 314         int i;
 315
 316         perf_mmap_free_page((unsigned long)rb->user_page);
 317         for (i = 0; i < rb->nr_pages; i++)
 318                 perf_mmap_free_page((unsigned long)rb->data_pages[i]);
 319         kfree(rb);
 320 }
 321
 322 #else
 323 static int data_page_nr(struct ring_buffer *rb)
 324 {
 325         return rb->nr_pages << page_order(rb);
 326 }
 327
 328 struct page *
 329 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
 330 {
 331         /* The '>' counts in the user page. */
 332         if (pgoff > data_page_nr(rb))
 333                 return NULL;
 334
 335         return vmalloc_to_page((void *)rb->user_page + pgoff * PAGE_SIZE);
 336 }
 337
 338 static void perf_mmap_unmark_page(void *addr)
 339 {
 340         struct page *page = vmalloc_to_page(addr);
 341
 342         page->mapping = NULL;
 343 }
 344
 345 static void rb_free_work(struct work_struct *work)
 346 {
 347         struct ring_buffer *rb;
 348         void *base;
 349         int i, nr;
 350
 351         rb = container_of(work, struct ring_buffer, work);
 352         nr = data_page_nr(rb);
 353
 354         base = rb->user_page;
 355         /* The '<=' counts in the user page. */
 356         for (i = 0; i <= nr; i++)
 357                 perf_mmap_unmark_page(base + (i * PAGE_SIZE));
 358
 359         vfree(base);
 360         kfree(rb);
 361 }
 362
 363 void rb_free(struct ring_buffer *rb)
 364 {
 365         schedule_work(&rb->work);
 366 }
 367
 368 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
 369 {
 370         struct ring_buffer *rb;
 371         unsigned long size;
 372         void *all_buf;
 373
 374         size = sizeof(struct ring_buffer);
 375         size += sizeof(void *);
 376
 377         rb = kzalloc(size, GFP_KERNEL);
 378         if (!rb)
 379                 goto fail;
 380
 381         INIT_WORK(&rb->work, rb_free_work);
 382
 383         all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE);
 384         if (!all_buf)
 385                 goto fail_all_buf;
 386
 387         rb->user_page = all_buf;
 388         rb->data_pages[0] = all_buf + PAGE_SIZE;
 389         rb->page_order = ilog2(nr_pages);
 390         rb->nr_pages = !!nr_pages;
 391
 392         ring_buffer_init(rb, watermark, flags);
 393
 394         return rb;
 395
 396 fail_all_buf:
 397         kfree(rb);
 398
 399 fail:
 400         return NULL;
 401 }
 402
 403 #endif