DPDK  20.08.0
rte_stack_lf_generic.h
1 /* SPDX-License-Identifier: BSD-3-Clause
2  * Copyright(c) 2019 Intel Corporation
3  */
4 
5 #ifndef _RTE_STACK_LF_GENERIC_H_
6 #define _RTE_STACK_LF_GENERIC_H_
7 
9 #include <rte_prefetch.h>
10 
11 static __rte_always_inline unsigned int
12 __rte_stack_lf_count(struct rte_stack *s)
13 {
14  /* stack_lf_push() and stack_lf_pop() do not update the list's contents
15  * and stack_lf->len atomically, which can cause the list to appear
16  * shorter than it actually is if this function is called while other
17  * threads are modifying the list.
18  *
19  * However, given the inherently approximate nature of the get_count
20  * callback -- even if the list and its size were updated atomically,
21  * the size could change between when get_count executes and when the
22  * value is returned to the caller -- this is acceptable.
23  *
24  * The stack_lf->len updates are placed such that the list may appear to
25  * have fewer elements than it does, but will never appear to have more
26  * elements. If the mempool is near-empty to the point that this is a
27  * concern, the user should consider increasing the mempool size.
28  */
29  return (unsigned int)rte_atomic64_read((rte_atomic64_t *)
30  &s->stack_lf.used.len);
31 }
32 
33 static __rte_always_inline void
34 __rte_stack_lf_push_elems(struct rte_stack_lf_list *list,
35  struct rte_stack_lf_elem *first,
36  struct rte_stack_lf_elem *last,
37  unsigned int num)
38 {
39  struct rte_stack_lf_head old_head;
40  int success;
41 
42  old_head = list->head;
43 
44  do {
45  struct rte_stack_lf_head new_head;
46 
47  /* An acquire fence (or stronger) is needed for weak memory
48  * models to establish a synchronized-with relationship between
49  * the list->head load and store-release operations (as part of
50  * the rte_atomic128_cmp_exchange()).
51  */
52  rte_smp_mb();
53 
54  /* Swing the top pointer to the first element in the list and
55  * make the last element point to the old top.
56  */
57  new_head.top = first;
58  new_head.cnt = old_head.cnt + 1;
59 
60  last->next = old_head.top;
61 
62  /* old_head is updated on failure */
64  (rte_int128_t *)&list->head,
65  (rte_int128_t *)&old_head,
66  (rte_int128_t *)&new_head,
67  1, __ATOMIC_RELEASE,
68  __ATOMIC_RELAXED);
69  } while (success == 0);
70 
71  rte_atomic64_add((rte_atomic64_t *)&list->len, num);
72 }
73 
74 static __rte_always_inline struct rte_stack_lf_elem *
75 __rte_stack_lf_pop_elems(struct rte_stack_lf_list *list,
76  unsigned int num,
77  void **obj_table,
78  struct rte_stack_lf_elem **last)
79 {
80  struct rte_stack_lf_head old_head;
81  int success;
82 
83  /* Reserve num elements, if available */
84  while (1) {
85  uint64_t len = rte_atomic64_read((rte_atomic64_t *)&list->len);
86 
87  /* Does the list contain enough elements? */
88  if (unlikely(len < num))
89  return NULL;
90 
91  if (rte_atomic64_cmpset((volatile uint64_t *)&list->len,
92  len, len - num))
93  break;
94  }
95 
96  old_head = list->head;
97 
98  /* Pop num elements */
99  do {
100  struct rte_stack_lf_head new_head;
101  struct rte_stack_lf_elem *tmp;
102  unsigned int i;
103 
104  /* An acquire fence (or stronger) is needed for weak memory
105  * models to ensure the LF LIFO element reads are properly
106  * ordered with respect to the head pointer read.
107  */
108  rte_smp_mb();
109 
110  rte_prefetch0(old_head.top);
111 
112  tmp = old_head.top;
113 
114  /* Traverse the list to find the new head. A next pointer will
115  * either point to another element or NULL; if a thread
116  * encounters a pointer that has already been popped, the CAS
117  * will fail.
118  */
119  for (i = 0; i < num && tmp != NULL; i++) {
120  rte_prefetch0(tmp->next);
121  if (obj_table)
122  obj_table[i] = tmp->data;
123  if (last)
124  *last = tmp;
125  tmp = tmp->next;
126  }
127 
128  /* If NULL was encountered, the list was modified while
129  * traversing it. Retry.
130  */
131  if (i != num)
132  continue;
133 
134  new_head.top = tmp;
135  new_head.cnt = old_head.cnt + 1;
136 
137  /* old_head is updated on failure */
138  success = rte_atomic128_cmp_exchange(
139  (rte_int128_t *)&list->head,
140  (rte_int128_t *)&old_head,
141  (rte_int128_t *)&new_head,
142  1, __ATOMIC_RELEASE,
143  __ATOMIC_RELAXED);
144  } while (success == 0);
145 
146  return old_head.top;
147 }
148 
149 #endif /* _RTE_STACK_LF_GENERIC_H_ */
#define __rte_always_inline
Definition: rte_common.h:202
static int64_t rte_atomic64_read(rte_atomic64_t *v)
#define unlikely(x)
static int rte_atomic64_cmpset(volatile uint64_t *dst, uint64_t exp, uint64_t src)
static void rte_smp_mb(void)
static __rte_experimental int rte_atomic128_cmp_exchange(rte_int128_t *dst, rte_int128_t *exp, const rte_int128_t *src, unsigned int weak, int success, int failure)
static void rte_prefetch0(const volatile void *p)
static void rte_atomic64_add(rte_atomic64_t *v, int64_t inc)