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 #include <linux/poll.h> 17 18 #include "internal.h" 19 20 static void perf_output_wakeup(struct perf_output_handle *handle) 21 { 22 atomic_set(&handle->rb->poll, POLLIN); 23 24 handle->event->pending_wakeup = 1; 25 irq_work_queue(&handle->event->pending); 26 } 27 28 /* 29 * We need to ensure a later event_id doesn't publish a head when a former 30 * event isn't done writing. However since we need to deal with NMIs we 31 * cannot fully serialize things. 32 * 33 * We only publish the head (and generate a wakeup) when the outer-most 34 * event completes. 35 */ 36 static void perf_output_get_handle(struct perf_output_handle *handle) 37 { 38 struct ring_buffer *rb = handle->rb; 39 40 preempt_disable(); 41 local_inc(&rb->nest); 42 handle->wakeup = local_read(&rb->wakeup); 43 } 44 45 static void perf_output_put_handle(struct perf_output_handle *handle) 46 { 47 struct ring_buffer *rb = handle->rb; 48 unsigned long head; 49 50 again: 51 head = local_read(&rb->head); 52 53 /* 54 * IRQ/NMI can happen here, which means we can miss a head update. 55 */ 56 57 if (!local_dec_and_test(&rb->nest)) 58 goto out; 59 60 /* 61 * Since the mmap() consumer (userspace) can run on a different CPU: 62 * 63 * kernel user 64 * 65 * if (LOAD ->data_tail) { LOAD ->data_head 66 * (A) smp_rmb() (C) 67 * STORE $data LOAD $data 68 * smp_wmb() (B) smp_mb() (D) 69 * STORE ->data_head STORE ->data_tail 70 * } 71 * 72 * Where A pairs with D, and B pairs with C. 73 * 74 * In our case (A) is a control dependency that separates the load of 75 * the ->data_tail and the stores of $data. In case ->data_tail 76 * indicates there is no room in the buffer to store $data we do not. 77 * 78 * D needs to be a full barrier since it separates the data READ 79 * from the tail WRITE. 80 * 81 * For B a WMB is sufficient since it separates two WRITEs, and for C 82 * an RMB is sufficient since it separates two READs. 83 * 84 * See perf_output_begin(). 85 */ 86 smp_wmb(); /* B, matches C */ 87 rb->user_page->data_head = head; 88 89 /* 90 * Now check if we missed an update -- rely on previous implied 91 * compiler barriers to force a re-read. 92 */ 93 if (unlikely(head != local_read(&rb->head))) { 94 local_inc(&rb->nest); 95 goto again; 96 } 97 98 if (handle->wakeup != local_read(&rb->wakeup)) 99 perf_output_wakeup(handle); 100 101 out: 102 preempt_enable(); 103 } 104 105 int perf_output_begin(struct perf_output_handle *handle, 106 struct perf_event *event, unsigned int size) 107 { 108 struct ring_buffer *rb; 109 unsigned long tail, offset, head; 110 int have_lost, page_shift; 111 struct { 112 struct perf_event_header header; 113 u64 id; 114 u64 lost; 115 } lost_event; 116 117 rcu_read_lock(); 118 /* 119 * For inherited events we send all the output towards the parent. 120 */ 121 if (event->parent) 122 event = event->parent; 123 124 rb = rcu_dereference(event->rb); 125 if (unlikely(!rb)) 126 goto out; 127 128 if (unlikely(!rb->nr_pages)) 129 goto out; 130 131 handle->rb = rb; 132 handle->event = event; 133 134 have_lost = local_read(&rb->lost); 135 if (unlikely(have_lost)) { 136 size += sizeof(lost_event); 137 if (event->attr.sample_id_all) 138 size += event->id_header_size; 139 } 140 141 perf_output_get_handle(handle); 142 143 do { 144 tail = ACCESS_ONCE(rb->user_page->data_tail); 145 offset = head = local_read(&rb->head); 146 if (!rb->overwrite && 147 unlikely(CIRC_SPACE(head, tail, perf_data_size(rb)) < size)) 148 goto fail; 149 150 /* 151 * The above forms a control dependency barrier separating the 152 * @tail load above from the data stores below. Since the @tail 153 * load is required to compute the branch to fail below. 154 * 155 * A, matches D; the full memory barrier userspace SHOULD issue 156 * after reading the data and before storing the new tail 157 * position. 158 * 159 * See perf_output_put_handle(). 160 */ 161 162 head += size; 163 } while (local_cmpxchg(&rb->head, offset, head) != offset); 164 165 /* 166 * We rely on the implied barrier() by local_cmpxchg() to ensure 167 * none of the data stores below can be lifted up by the compiler. 168 */ 169 170 if (unlikely(head - local_read(&rb->wakeup) > rb->watermark)) 171 local_add(rb->watermark, &rb->wakeup); 172 173 page_shift = PAGE_SHIFT + page_order(rb); 174 175 handle->page = (offset >> page_shift) & (rb->nr_pages - 1); 176 offset &= (1UL << page_shift) - 1; 177 handle->addr = rb->data_pages[handle->page] + offset; 178 handle->size = (1UL << page_shift) - offset; 179 180 if (unlikely(have_lost)) { 181 struct perf_sample_data sample_data; 182 183 lost_event.header.size = sizeof(lost_event); 184 lost_event.header.type = PERF_RECORD_LOST; 185 lost_event.header.misc = 0; 186 lost_event.id = event->id; 187 lost_event.lost = local_xchg(&rb->lost, 0); 188 189 perf_event_header__init_id(&lost_event.header, 190 &sample_data, event); 191 perf_output_put(handle, lost_event); 192 perf_event__output_id_sample(event, handle, &sample_data); 193 } 194 195 return 0; 196 197 fail: 198 local_inc(&rb->lost); 199 perf_output_put_handle(handle); 200 out: 201 rcu_read_unlock(); 202 203 return -ENOSPC; 204 } 205 206 unsigned int perf_output_copy(struct perf_output_handle *handle, 207 const void *buf, unsigned int len) 208 { 209 return __output_copy(handle, buf, len); 210 } 211 212 unsigned int perf_output_skip(struct perf_output_handle *handle, 213 unsigned int len) 214 { 215 return __output_skip(handle, NULL, len); 216 } 217 218 void perf_output_end(struct perf_output_handle *handle) 219 { 220 perf_output_put_handle(handle); 221 rcu_read_unlock(); 222 } 223 224 static void 225 ring_buffer_init(struct ring_buffer *rb, long watermark, int flags) 226 { 227 long max_size = perf_data_size(rb); 228 229 if (watermark) 230 rb->watermark = min(max_size, watermark); 231 232 if (!rb->watermark) 233 rb->watermark = max_size / 2; 234 235 if (flags & RING_BUFFER_WRITABLE) 236 rb->overwrite = 0; 237 else 238 rb->overwrite = 1; 239 240 atomic_set(&rb->refcount, 1); 241 242 INIT_LIST_HEAD(&rb->event_list); 243 spin_lock_init(&rb->event_lock); 244 } 245 246 #ifndef CONFIG_PERF_USE_VMALLOC 247 248 /* 249 * Back perf_mmap() with regular GFP_KERNEL-0 pages. 250 */ 251 252 struct page * 253 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff) 254 { 255 if (pgoff > rb->nr_pages) 256 return NULL; 257 258 if (pgoff == 0) 259 return virt_to_page(rb->user_page); 260 261 return virt_to_page(rb->data_pages[pgoff - 1]); 262 } 263 264 static void *perf_mmap_alloc_page(int cpu) 265 { 266 struct page *page; 267 int node; 268 269 node = (cpu == -1) ? cpu : cpu_to_node(cpu); 270 page = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0); 271 if (!page) 272 return NULL; 273 274 return page_address(page); 275 } 276 277 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags) 278 { 279 struct ring_buffer *rb; 280 unsigned long size; 281 int i; 282 283 size = sizeof(struct ring_buffer); 284 size += nr_pages * sizeof(void *); 285 286 rb = kzalloc(size, GFP_KERNEL); 287 if (!rb) 288 goto fail; 289 290 rb->user_page = perf_mmap_alloc_page(cpu); 291 if (!rb->user_page) 292 goto fail_user_page; 293 294 for (i = 0; i < nr_pages; i++) { 295 rb->data_pages[i] = perf_mmap_alloc_page(cpu); 296 if (!rb->data_pages[i]) 297 goto fail_data_pages; 298 } 299 300 rb->nr_pages = nr_pages; 301 302 ring_buffer_init(rb, watermark, flags); 303 304 return rb; 305 306 fail_data_pages: 307 for (i--; i >= 0; i--) 308 free_page((unsigned long)rb->data_pages[i]); 309 310 free_page((unsigned long)rb->user_page); 311 312 fail_user_page: 313 kfree(rb); 314 315 fail: 316 return NULL; 317 } 318 319 static void perf_mmap_free_page(unsigned long addr) 320 { 321 struct page *page = virt_to_page((void *)addr); 322 323 page->mapping = NULL; 324 __free_page(page); 325 } 326 327 void rb_free(struct ring_buffer *rb) 328 { 329 int i; 330 331 perf_mmap_free_page((unsigned long)rb->user_page); 332 for (i = 0; i < rb->nr_pages; i++) 333 perf_mmap_free_page((unsigned long)rb->data_pages[i]); 334 kfree(rb); 335 } 336 337 #else 338 static int data_page_nr(struct ring_buffer *rb) 339 { 340 return rb->nr_pages << page_order(rb); 341 } 342 343 struct page * 344 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff) 345 { 346 /* The '>' counts in the user page. */ 347 if (pgoff > data_page_nr(rb)) 348 return NULL; 349 350 return vmalloc_to_page((void *)rb->user_page + pgoff * PAGE_SIZE); 351 } 352 353 static void perf_mmap_unmark_page(void *addr) 354 { 355 struct page *page = vmalloc_to_page(addr); 356 357 page->mapping = NULL; 358 } 359 360 static void rb_free_work(struct work_struct *work) 361 { 362 struct ring_buffer *rb; 363 void *base; 364 int i, nr; 365 366 rb = container_of(work, struct ring_buffer, work); 367 nr = data_page_nr(rb); 368 369 base = rb->user_page; 370 /* The '<=' counts in the user page. */ 371 for (i = 0; i <= nr; i++) 372 perf_mmap_unmark_page(base + (i * PAGE_SIZE)); 373 374 vfree(base); 375 kfree(rb); 376 } 377 378 void rb_free(struct ring_buffer *rb) 379 { 380 schedule_work(&rb->work); 381 } 382 383 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags) 384 { 385 struct ring_buffer *rb; 386 unsigned long size; 387 void *all_buf; 388 389 size = sizeof(struct ring_buffer); 390 size += sizeof(void *); 391 392 rb = kzalloc(size, GFP_KERNEL); 393 if (!rb) 394 goto fail; 395 396 INIT_WORK(&rb->work, rb_free_work); 397 398 all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE); 399 if (!all_buf) 400 goto fail_all_buf; 401 402 rb->user_page = all_buf; 403 rb->data_pages[0] = all_buf + PAGE_SIZE; 404 rb->page_order = ilog2(nr_pages); 405 rb->nr_pages = !!nr_pages; 406 407 ring_buffer_init(rb, watermark, flags); 408 409 return rb; 410 411 fail_all_buf: 412 kfree(rb); 413 414 fail: 415 return NULL; 416 } 417 418 #endif 419