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