xref: /linux/kernel/events/ring_buffer.c (revision 3932b9ca55b0be314a36d3e84faff3e823c081f5)
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 
17 #include "internal.h"
18 
19 static void perf_output_wakeup(struct perf_output_handle *handle)
20 {
21 	atomic_set(&handle->rb->poll, POLL_IN);
22 
23 	handle->event->pending_wakeup = 1;
24 	irq_work_queue(&handle->event->pending);
25 }
26 
27 /*
28  * We need to ensure a later event_id doesn't publish a head when a former
29  * event isn't done writing. However since we need to deal with NMIs we
30  * cannot fully serialize things.
31  *
32  * We only publish the head (and generate a wakeup) when the outer-most
33  * event completes.
34  */
35 static void perf_output_get_handle(struct perf_output_handle *handle)
36 {
37 	struct ring_buffer *rb = handle->rb;
38 
39 	preempt_disable();
40 	local_inc(&rb->nest);
41 	handle->wakeup = local_read(&rb->wakeup);
42 }
43 
44 static void perf_output_put_handle(struct perf_output_handle *handle)
45 {
46 	struct ring_buffer *rb = handle->rb;
47 	unsigned long head;
48 
49 again:
50 	head = local_read(&rb->head);
51 
52 	/*
53 	 * IRQ/NMI can happen here, which means we can miss a head update.
54 	 */
55 
56 	if (!local_dec_and_test(&rb->nest))
57 		goto out;
58 
59 	/*
60 	 * Since the mmap() consumer (userspace) can run on a different CPU:
61 	 *
62 	 *   kernel				user
63 	 *
64 	 *   if (LOAD ->data_tail) {		LOAD ->data_head
65 	 *			(A)		smp_rmb()	(C)
66 	 *	STORE $data			LOAD $data
67 	 *	smp_wmb()	(B)		smp_mb()	(D)
68 	 *	STORE ->data_head		STORE ->data_tail
69 	 *   }
70 	 *
71 	 * Where A pairs with D, and B pairs with C.
72 	 *
73 	 * In our case (A) is a control dependency that separates the load of
74 	 * the ->data_tail and the stores of $data. In case ->data_tail
75 	 * indicates there is no room in the buffer to store $data we do not.
76 	 *
77 	 * D needs to be a full barrier since it separates the data READ
78 	 * from the tail WRITE.
79 	 *
80 	 * For B a WMB is sufficient since it separates two WRITEs, and for C
81 	 * an RMB is sufficient since it separates two READs.
82 	 *
83 	 * See perf_output_begin().
84 	 */
85 	smp_wmb(); /* B, matches C */
86 	rb->user_page->data_head = head;
87 
88 	/*
89 	 * Now check if we missed an update -- rely on previous implied
90 	 * compiler barriers to force a re-read.
91 	 */
92 	if (unlikely(head != local_read(&rb->head))) {
93 		local_inc(&rb->nest);
94 		goto again;
95 	}
96 
97 	if (handle->wakeup != local_read(&rb->wakeup))
98 		perf_output_wakeup(handle);
99 
100 out:
101 	preempt_enable();
102 }
103 
104 int perf_output_begin(struct perf_output_handle *handle,
105 		      struct perf_event *event, unsigned int size)
106 {
107 	struct ring_buffer *rb;
108 	unsigned long tail, offset, head;
109 	int have_lost, page_shift;
110 	struct {
111 		struct perf_event_header header;
112 		u64			 id;
113 		u64			 lost;
114 	} lost_event;
115 
116 	rcu_read_lock();
117 	/*
118 	 * For inherited events we send all the output towards the parent.
119 	 */
120 	if (event->parent)
121 		event = event->parent;
122 
123 	rb = rcu_dereference(event->rb);
124 	if (unlikely(!rb))
125 		goto out;
126 
127 	if (unlikely(!rb->nr_pages))
128 		goto out;
129 
130 	handle->rb    = rb;
131 	handle->event = event;
132 
133 	have_lost = local_read(&rb->lost);
134 	if (unlikely(have_lost)) {
135 		size += sizeof(lost_event);
136 		if (event->attr.sample_id_all)
137 			size += event->id_header_size;
138 	}
139 
140 	perf_output_get_handle(handle);
141 
142 	do {
143 		tail = ACCESS_ONCE(rb->user_page->data_tail);
144 		offset = head = local_read(&rb->head);
145 		if (!rb->overwrite &&
146 		    unlikely(CIRC_SPACE(head, tail, perf_data_size(rb)) < size))
147 			goto fail;
148 
149 		/*
150 		 * The above forms a control dependency barrier separating the
151 		 * @tail load above from the data stores below. Since the @tail
152 		 * load is required to compute the branch to fail below.
153 		 *
154 		 * A, matches D; the full memory barrier userspace SHOULD issue
155 		 * after reading the data and before storing the new tail
156 		 * position.
157 		 *
158 		 * See perf_output_put_handle().
159 		 */
160 
161 		head += size;
162 	} while (local_cmpxchg(&rb->head, offset, head) != offset);
163 
164 	/*
165 	 * We rely on the implied barrier() by local_cmpxchg() to ensure
166 	 * none of the data stores below can be lifted up by the compiler.
167 	 */
168 
169 	if (unlikely(head - local_read(&rb->wakeup) > rb->watermark))
170 		local_add(rb->watermark, &rb->wakeup);
171 
172 	page_shift = PAGE_SHIFT + page_order(rb);
173 
174 	handle->page = (offset >> page_shift) & (rb->nr_pages - 1);
175 	offset &= (1UL << page_shift) - 1;
176 	handle->addr = rb->data_pages[handle->page] + offset;
177 	handle->size = (1UL << page_shift) - offset;
178 
179 	if (unlikely(have_lost)) {
180 		struct perf_sample_data sample_data;
181 
182 		lost_event.header.size = sizeof(lost_event);
183 		lost_event.header.type = PERF_RECORD_LOST;
184 		lost_event.header.misc = 0;
185 		lost_event.id          = event->id;
186 		lost_event.lost        = local_xchg(&rb->lost, 0);
187 
188 		perf_event_header__init_id(&lost_event.header,
189 					   &sample_data, event);
190 		perf_output_put(handle, lost_event);
191 		perf_event__output_id_sample(event, handle, &sample_data);
192 	}
193 
194 	return 0;
195 
196 fail:
197 	local_inc(&rb->lost);
198 	perf_output_put_handle(handle);
199 out:
200 	rcu_read_unlock();
201 
202 	return -ENOSPC;
203 }
204 
205 unsigned int perf_output_copy(struct perf_output_handle *handle,
206 		      const void *buf, unsigned int len)
207 {
208 	return __output_copy(handle, buf, len);
209 }
210 
211 unsigned int perf_output_skip(struct perf_output_handle *handle,
212 			      unsigned int len)
213 {
214 	return __output_skip(handle, NULL, len);
215 }
216 
217 void perf_output_end(struct perf_output_handle *handle)
218 {
219 	perf_output_put_handle(handle);
220 	rcu_read_unlock();
221 }
222 
223 static void
224 ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
225 {
226 	long max_size = perf_data_size(rb);
227 
228 	if (watermark)
229 		rb->watermark = min(max_size, watermark);
230 
231 	if (!rb->watermark)
232 		rb->watermark = max_size / 2;
233 
234 	if (flags & RING_BUFFER_WRITABLE)
235 		rb->overwrite = 0;
236 	else
237 		rb->overwrite = 1;
238 
239 	atomic_set(&rb->refcount, 1);
240 
241 	INIT_LIST_HEAD(&rb->event_list);
242 	spin_lock_init(&rb->event_lock);
243 }
244 
245 #ifndef CONFIG_PERF_USE_VMALLOC
246 
247 /*
248  * Back perf_mmap() with regular GFP_KERNEL-0 pages.
249  */
250 
251 struct page *
252 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
253 {
254 	if (pgoff > rb->nr_pages)
255 		return NULL;
256 
257 	if (pgoff == 0)
258 		return virt_to_page(rb->user_page);
259 
260 	return virt_to_page(rb->data_pages[pgoff - 1]);
261 }
262 
263 static void *perf_mmap_alloc_page(int cpu)
264 {
265 	struct page *page;
266 	int node;
267 
268 	node = (cpu == -1) ? cpu : cpu_to_node(cpu);
269 	page = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0);
270 	if (!page)
271 		return NULL;
272 
273 	return page_address(page);
274 }
275 
276 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
277 {
278 	struct ring_buffer *rb;
279 	unsigned long size;
280 	int i;
281 
282 	size = sizeof(struct ring_buffer);
283 	size += nr_pages * sizeof(void *);
284 
285 	rb = kzalloc(size, GFP_KERNEL);
286 	if (!rb)
287 		goto fail;
288 
289 	rb->user_page = perf_mmap_alloc_page(cpu);
290 	if (!rb->user_page)
291 		goto fail_user_page;
292 
293 	for (i = 0; i < nr_pages; i++) {
294 		rb->data_pages[i] = perf_mmap_alloc_page(cpu);
295 		if (!rb->data_pages[i])
296 			goto fail_data_pages;
297 	}
298 
299 	rb->nr_pages = nr_pages;
300 
301 	ring_buffer_init(rb, watermark, flags);
302 
303 	return rb;
304 
305 fail_data_pages:
306 	for (i--; i >= 0; i--)
307 		free_page((unsigned long)rb->data_pages[i]);
308 
309 	free_page((unsigned long)rb->user_page);
310 
311 fail_user_page:
312 	kfree(rb);
313 
314 fail:
315 	return NULL;
316 }
317 
318 static void perf_mmap_free_page(unsigned long addr)
319 {
320 	struct page *page = virt_to_page((void *)addr);
321 
322 	page->mapping = NULL;
323 	__free_page(page);
324 }
325 
326 void rb_free(struct ring_buffer *rb)
327 {
328 	int i;
329 
330 	perf_mmap_free_page((unsigned long)rb->user_page);
331 	for (i = 0; i < rb->nr_pages; i++)
332 		perf_mmap_free_page((unsigned long)rb->data_pages[i]);
333 	kfree(rb);
334 }
335 
336 #else
337 static int data_page_nr(struct ring_buffer *rb)
338 {
339 	return rb->nr_pages << page_order(rb);
340 }
341 
342 struct page *
343 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
344 {
345 	/* The '>' counts in the user page. */
346 	if (pgoff > data_page_nr(rb))
347 		return NULL;
348 
349 	return vmalloc_to_page((void *)rb->user_page + pgoff * PAGE_SIZE);
350 }
351 
352 static void perf_mmap_unmark_page(void *addr)
353 {
354 	struct page *page = vmalloc_to_page(addr);
355 
356 	page->mapping = NULL;
357 }
358 
359 static void rb_free_work(struct work_struct *work)
360 {
361 	struct ring_buffer *rb;
362 	void *base;
363 	int i, nr;
364 
365 	rb = container_of(work, struct ring_buffer, work);
366 	nr = data_page_nr(rb);
367 
368 	base = rb->user_page;
369 	/* The '<=' counts in the user page. */
370 	for (i = 0; i <= nr; i++)
371 		perf_mmap_unmark_page(base + (i * PAGE_SIZE));
372 
373 	vfree(base);
374 	kfree(rb);
375 }
376 
377 void rb_free(struct ring_buffer *rb)
378 {
379 	schedule_work(&rb->work);
380 }
381 
382 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
383 {
384 	struct ring_buffer *rb;
385 	unsigned long size;
386 	void *all_buf;
387 
388 	size = sizeof(struct ring_buffer);
389 	size += sizeof(void *);
390 
391 	rb = kzalloc(size, GFP_KERNEL);
392 	if (!rb)
393 		goto fail;
394 
395 	INIT_WORK(&rb->work, rb_free_work);
396 
397 	all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE);
398 	if (!all_buf)
399 		goto fail_all_buf;
400 
401 	rb->user_page = all_buf;
402 	rb->data_pages[0] = all_buf + PAGE_SIZE;
403 	rb->page_order = ilog2(nr_pages);
404 	rb->nr_pages = !!nr_pages;
405 
406 	ring_buffer_init(rb, watermark, flags);
407 
408 	return rb;
409 
410 fail_all_buf:
411 	kfree(rb);
412 
413 fail:
414 	return NULL;
415 }
416 
417 #endif
418