Root/kernel/events/ring_buffer.c

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
18static 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
37static 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 */
53static 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
62static void perf_output_put_handle(struct perf_output_handle *handle)
63{
64    struct ring_buffer *rb = handle->rb;
65    unsigned long head;
66
67again:
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
96out:
97    preempt_enable();
98}
99
100int 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
176fail:
177    local_inc(&rb->lost);
178    perf_output_put_handle(handle);
179out:
180    rcu_read_unlock();
181
182    return -ENOSPC;
183}
184
185void perf_output_copy(struct perf_output_handle *handle,
186              const void *buf, unsigned int len)
187{
188    __output_copy(handle, buf, len);
189}
190
191void perf_output_end(struct perf_output_handle *handle)
192{
193    perf_output_put_handle(handle);
194    rcu_read_unlock();
195}
196
197static void
198ring_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
223struct page *
224perf_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
235static 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
248struct 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
277fail_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
283fail_user_page:
284    kfree(rb);
285
286fail:
287    return NULL;
288}
289
290static 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
298void 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
310struct page *
311perf_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
319static void perf_mmap_unmark_page(void *addr)
320{
321    struct page *page = vmalloc_to_page(addr);
322
323    page->mapping = NULL;
324}
325
326static 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
343void rb_free(struct ring_buffer *rb)
344{
345    schedule_work(&rb->work);
346}
347
348struct 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
376fail_all_buf:
377    kfree(rb);
378
379fail:
380    return NULL;
381}
382
383#endif
384

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