DPDK  18.05.1
rte_ring_generic.h
1 /* SPDX-License-Identifier: BSD-3-Clause
2  *
3  * Copyright (c) 2010-2017 Intel Corporation
4  * Copyright (c) 2007-2009 Kip Macy kmacy@freebsd.org
5  * All rights reserved.
6  * Derived from FreeBSD's bufring.h
7  * Used as BSD-3 Licensed with permission from Kip Macy.
8  */
9 
10 #ifndef _RTE_RING_GENERIC_H_
11 #define _RTE_RING_GENERIC_H_
12 
13 static __rte_always_inline void
14 update_tail(struct rte_ring_headtail *ht, uint32_t old_val, uint32_t new_val,
15  uint32_t single, uint32_t enqueue)
16 {
17  if (enqueue)
18  rte_smp_wmb();
19  else
20  rte_smp_rmb();
21  /*
22  * If there are other enqueues/dequeues in progress that preceded us,
23  * we need to wait for them to complete
24  */
25  if (!single)
26  while (unlikely(ht->tail != old_val))
27  rte_pause();
28 
29  ht->tail = new_val;
30 }
31 
55 static __rte_always_inline unsigned int
56 __rte_ring_move_prod_head(struct rte_ring *r, unsigned int is_sp,
57  unsigned int n, enum rte_ring_queue_behavior behavior,
58  uint32_t *old_head, uint32_t *new_head,
59  uint32_t *free_entries)
60 {
61  const uint32_t capacity = r->capacity;
62  unsigned int max = n;
63  int success;
64 
65  do {
66  /* Reset n to the initial burst count */
67  n = max;
68 
69  *old_head = r->prod.head;
70 
71  /* add rmb barrier to avoid load/load reorder in weak
72  * memory model. It is noop on x86
73  */
74  rte_smp_rmb();
75 
76  /*
77  * The subtraction is done between two unsigned 32bits value
78  * (the result is always modulo 32 bits even if we have
79  * *old_head > cons_tail). So 'free_entries' is always between 0
80  * and capacity (which is < size).
81  */
82  *free_entries = (capacity + r->cons.tail - *old_head);
83 
84  /* check that we have enough room in ring */
85  if (unlikely(n > *free_entries))
86  n = (behavior == RTE_RING_QUEUE_FIXED) ?
87  0 : *free_entries;
88 
89  if (n == 0)
90  return 0;
91 
92  *new_head = *old_head + n;
93  if (is_sp)
94  r->prod.head = *new_head, success = 1;
95  else
96  success = rte_atomic32_cmpset(&r->prod.head,
97  *old_head, *new_head);
98  } while (unlikely(success == 0));
99  return n;
100 }
101 
125 static __rte_always_inline unsigned int
126 __rte_ring_move_cons_head(struct rte_ring *r, unsigned int is_sc,
127  unsigned int n, enum rte_ring_queue_behavior behavior,
128  uint32_t *old_head, uint32_t *new_head,
129  uint32_t *entries)
130 {
131  unsigned int max = n;
132  int success;
133 
134  /* move cons.head atomically */
135  do {
136  /* Restore n as it may change every loop */
137  n = max;
138 
139  *old_head = r->cons.head;
140 
141  /* add rmb barrier to avoid load/load reorder in weak
142  * memory model. It is noop on x86
143  */
144  rte_smp_rmb();
145 
146  /* The subtraction is done between two unsigned 32bits value
147  * (the result is always modulo 32 bits even if we have
148  * cons_head > prod_tail). So 'entries' is always between 0
149  * and size(ring)-1.
150  */
151  *entries = (r->prod.tail - *old_head);
152 
153  /* Set the actual entries for dequeue */
154  if (n > *entries)
155  n = (behavior == RTE_RING_QUEUE_FIXED) ? 0 : *entries;
156 
157  if (unlikely(n == 0))
158  return 0;
159 
160  *new_head = *old_head + n;
161  if (is_sc)
162  r->cons.head = *new_head, success = 1;
163  else
164  success = rte_atomic32_cmpset(&r->cons.head, *old_head,
165  *new_head);
166  } while (unlikely(success == 0));
167  return n;
168 }
169 
170 #endif /* _RTE_RING_GENERIC_H_ */