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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 #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 

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