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 18 static 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 37 static 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 */ 53 static 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 62 static void perf_output_put_handle(struct perf_output_handle *handle) 63 { 64 struct ring_buffer *rb = handle->rb; 65 unsigned long head; 66 67 again: 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 96 out: 97 preempt_enable(); 98 } 99 100 int 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; 175 176 fail: 177 local_inc(&rb->lost); 178 perf_output_put_handle(handle); 179 out: 180 rcu_read_unlock(); 181 182 return -ENOSPC; 183 } 184 185 unsigned int perf_output_copy(struct perf_output_handle *handle, 186 const void *buf, unsigned int len) 187 { 188 return __output_copy(handle, buf, len); 189 } 190 191 unsigned int perf_output_skip(struct perf_output_handle *handle, 192 unsigned int len) 193 { 194 return __output_skip(handle, NULL, len); 195 } 196 197 void perf_output_end(struct perf_output_handle *handle) 198 { 199 perf_output_put_handle(handle); 200 rcu_read_unlock(); 201 } 202 203 static void 204 ring_buffer_init(struct ring_buffer *rb, long watermark, int flags) 205 { 206 long max_size = perf_data_size(rb); 207 208 if (watermark) 209 rb->watermark = min(max_size, watermark); 210 211 if (!rb->watermark) 212 rb->watermark = max_size / 2; 213 214 if (flags & RING_BUFFER_WRITABLE) 215 rb->writable = 1; 216 217 atomic_set(&rb->refcount, 1); 218 219 INIT_LIST_HEAD(&rb->event_list); 220 spin_lock_init(&rb->event_lock); 221 } 222 223 #ifndef CONFIG_PERF_USE_VMALLOC 224 225 /* 226 * Back perf_mmap() with regular GFP_KERNEL-0 pages. 227 */ 228 229 struct page * 230 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff) 231 { 232 if (pgoff > rb->nr_pages) 233 return NULL; 234 235 if (pgoff == 0) 236 return virt_to_page(rb->user_page); 237 238 return virt_to_page(rb->data_pages[pgoff - 1]); 239 } 240 241 static void *perf_mmap_alloc_page(int cpu) 242 { 243 struct page *page; 244 int node; 245 246 node = (cpu == -1) ? cpu : cpu_to_node(cpu); 247 page = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0); 248 if (!page) 249 return NULL; 250 251 return page_address(page); 252 } 253 254 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags) 255 { 256 struct ring_buffer *rb; 257 unsigned long size; 258 int i; 259 260 size = sizeof(struct ring_buffer); 261 size += nr_pages * sizeof(void *); 262 263 rb = kzalloc(size, GFP_KERNEL); 264 if (!rb) 265 goto fail; 266 267 rb->user_page = perf_mmap_alloc_page(cpu); 268 if (!rb->user_page) 269 goto fail_user_page; 270 271 for (i = 0; i < nr_pages; i++) { 272 rb->data_pages[i] = perf_mmap_alloc_page(cpu); 273 if (!rb->data_pages[i]) 274 goto fail_data_pages; 275 } 276 277 rb->nr_pages = nr_pages; 278 279 ring_buffer_init(rb, watermark, flags); 280 281 return rb; 282 283 fail_data_pages: 284 for (i--; i >= 0; i--) 285 free_page((unsigned long)rb->data_pages[i]); 286 287 free_page((unsigned long)rb->user_page); 288 289 fail_user_page: 290 kfree(rb); 291 292 fail: 293 return NULL; 294 } 295 296 static void perf_mmap_free_page(unsigned long addr) 297 { 298 struct page *page = virt_to_page((void *)addr); 299 300 page->mapping = NULL; 301 __free_page(page); 302 } 303 304 void rb_free(struct ring_buffer *rb) 305 { 306 int i; 307 308 perf_mmap_free_page((unsigned long)rb->user_page); 309 for (i = 0; i < rb->nr_pages; i++) 310 perf_mmap_free_page((unsigned long)rb->data_pages[i]); 311 kfree(rb); 312 } 313 314 #else 315 316 struct page * 317 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff) 318 { 319 if (pgoff > (1UL << page_order(rb))) 320 return NULL; 321 322 return vmalloc_to_page((void *)rb->user_page + pgoff * PAGE_SIZE); 323 } 324 325 static void perf_mmap_unmark_page(void *addr) 326 { 327 struct page *page = vmalloc_to_page(addr); 328 329 page->mapping = NULL; 330 } 331 332 static void rb_free_work(struct work_struct *work) 333 { 334 struct ring_buffer *rb; 335 void *base; 336 int i, nr; 337 338 rb = container_of(work, struct ring_buffer, work); 339 nr = 1 << page_order(rb); 340 341 base = rb->user_page; 342 for (i = 0; i < nr + 1; i++) 343 perf_mmap_unmark_page(base + (i * PAGE_SIZE)); 344 345 vfree(base); 346 kfree(rb); 347 } 348 349 void rb_free(struct ring_buffer *rb) 350 { 351 schedule_work(&rb->work); 352 } 353 354 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags) 355 { 356 struct ring_buffer *rb; 357 unsigned long size; 358 void *all_buf; 359 360 size = sizeof(struct ring_buffer); 361 size += sizeof(void *); 362 363 rb = kzalloc(size, GFP_KERNEL); 364 if (!rb) 365 goto fail; 366 367 INIT_WORK(&rb->work, rb_free_work); 368 369 all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE); 370 if (!all_buf) 371 goto fail_all_buf; 372 373 rb->user_page = all_buf; 374 rb->data_pages[0] = all_buf + PAGE_SIZE; 375 rb->page_order = ilog2(nr_pages); 376 rb->nr_pages = 1; 377 378 ring_buffer_init(rb, watermark, flags); 379 380 return rb; 381 382 fail_all_buf: 383 kfree(rb); 384 385 fail: 386 return NULL; 387 } 388 389 #endif 390