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 void perf_output_copy(struct perf_output_handle *handle, 186 const void *buf, unsigned int len) 187 { 188 __output_copy(handle, buf, len); 189 } 190 191 void perf_output_end(struct perf_output_handle *handle) 192 { 193 perf_output_put_handle(handle); 194 rcu_read_unlock(); 195 } 196 197 static void 198 ring_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 */ 222 223 struct page * 224 perf_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 } 234 235 static 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 } 247 248 struct 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; 276 277 fail_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); 282 283 fail_user_page: 284 kfree(rb); 285 286 fail: 287 return NULL; 288 } 289 290 static 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 } 297 298 void 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 309 310 struct page * 311 perf_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 } 318 319 static void perf_mmap_unmark_page(void *addr) 320 { 321 struct page *page = vmalloc_to_page(addr); 322 323 page->mapping = NULL; 324 } 325 326 static 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 } 342 343 void rb_free(struct ring_buffer *rb) 344 { 345 schedule_work(&rb->work); 346 } 347 348 struct 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; 375 376 fail_all_buf: 377 kfree(rb); 378 379 fail: 380 return NULL; 381 } 382 383 #endif 384