1 /* SPDX-License-Identifier: BSD-3-Clause
2 * Copyright(c) 2019 Intel Corporation
5 #ifndef _RTE_STACK_LF_C11_H_
6 #define _RTE_STACK_LF_C11_H_
8 #include <rte_branch_prediction.h>
9 #include <rte_prefetch.h>
11 static __rte_always_inline unsigned int
12 __rte_stack_lf_count(struct rte_stack *s)
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.
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.
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.
29 return (unsigned int)__atomic_load_n(&s->stack_lf.used.len,
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,
39 struct rte_stack_lf_head old_head;
42 old_head = list->head;
45 struct rte_stack_lf_head new_head;
47 /* Use an acquire fence to establish a synchronized-with
48 * relationship between the list->head load and store-release
49 * operations (as part of the rte_atomic128_cmp_exchange()).
51 __atomic_thread_fence(__ATOMIC_ACQUIRE);
53 /* Swing the top pointer to the first element in the list and
54 * make the last element point to the old top.
57 new_head.cnt = old_head.cnt + 1;
59 last->next = old_head.top;
61 /* Use the release memmodel to ensure the writes to the LF LIFO
62 * elements are visible before the head pointer write.
64 success = rte_atomic128_cmp_exchange(
65 (rte_int128_t *)&list->head,
66 (rte_int128_t *)&old_head,
67 (rte_int128_t *)&new_head,
70 } while (success == 0);
72 /* Ensure the stack modifications are not reordered with respect
73 * to the LIFO len update.
75 __atomic_add_fetch(&list->len, num, __ATOMIC_RELEASE);
78 static __rte_always_inline struct rte_stack_lf_elem *
79 __rte_stack_lf_pop_elems(struct rte_stack_lf_list *list,
82 struct rte_stack_lf_elem **last)
84 struct rte_stack_lf_head old_head;
88 /* Reserve num elements, if available */
89 len = __atomic_load_n(&list->len, __ATOMIC_ACQUIRE);
92 /* Does the list contain enough elements? */
93 if (unlikely(len < num))
96 /* len is updated on failure */
97 if (__atomic_compare_exchange_n(&list->len,
104 /* If a torn read occurs, the CAS will fail and set old_head to the
105 * correct/latest value.
107 old_head = list->head;
109 /* Pop num elements */
111 struct rte_stack_lf_head new_head;
112 struct rte_stack_lf_elem *tmp;
115 /* Use the acquire memmodel to ensure the reads to the LF LIFO
116 * elements are properly ordered with respect to the head
119 __atomic_thread_fence(__ATOMIC_ACQUIRE);
121 rte_prefetch0(old_head.top);
125 /* Traverse the list to find the new head. A next pointer will
126 * either point to another element or NULL; if a thread
127 * encounters a pointer that has already been popped, the CAS
130 for (i = 0; i < num && tmp != NULL; i++) {
131 rte_prefetch0(tmp->next);
133 obj_table[i] = tmp->data;
139 /* If NULL was encountered, the list was modified while
140 * traversing it. Retry.
146 new_head.cnt = old_head.cnt + 1;
148 success = rte_atomic128_cmp_exchange(
149 (rte_int128_t *)&list->head,
150 (rte_int128_t *)&old_head,
151 (rte_int128_t *)&new_head,
154 } while (success == 0);
159 #endif /* _RTE_STACK_LF_C11_H_ */