1 /* SPDX-License-Identifier: BSD-3-Clause
2 * Copyright(c) 2019 Intel Corporation
5 #ifndef _RTE_STACK_LF_GENERIC_H_
6 #define _RTE_STACK_LF_GENERIC_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)rte_atomic64_read(&s->stack_lf.used.len);
32 static __rte_always_inline void
33 __rte_stack_lf_push_elems(struct rte_stack_lf_list *list,
34 struct rte_stack_lf_elem *first,
35 struct rte_stack_lf_elem *last,
38 #ifndef RTE_ARCH_X86_64
44 struct rte_stack_lf_head old_head;
47 old_head = list->head;
50 struct rte_stack_lf_head new_head;
52 /* An acquire fence (or stronger) is needed for weak memory
53 * models to establish a synchronized-with relationship between
54 * the list->head load and store-release operations (as part of
55 * the rte_atomic128_cmp_exchange()).
59 /* Swing the top pointer to the first element in the list and
60 * make the last element point to the old top.
63 new_head.cnt = old_head.cnt + 1;
65 last->next = old_head.top;
67 /* old_head is updated on failure */
68 success = rte_atomic128_cmp_exchange(
69 (rte_int128_t *)&list->head,
70 (rte_int128_t *)&old_head,
71 (rte_int128_t *)&new_head,
74 } while (success == 0);
76 rte_atomic64_add(&list->len, num);
80 static __rte_always_inline struct rte_stack_lf_elem *
81 __rte_stack_lf_pop_elems(struct rte_stack_lf_list *list,
84 struct rte_stack_lf_elem **last)
86 #ifndef RTE_ARCH_X86_64
87 RTE_SET_USED(obj_table);
94 struct rte_stack_lf_head old_head;
97 /* Reserve num elements, if available */
99 uint64_t len = rte_atomic64_read(&list->len);
101 /* Does the list contain enough elements? */
102 if (unlikely(len < num))
105 if (rte_atomic64_cmpset((volatile uint64_t *)&list->len,
110 old_head = list->head;
112 /* Pop num elements */
114 struct rte_stack_lf_head new_head;
115 struct rte_stack_lf_elem *tmp;
118 /* An acquire fence (or stronger) is needed for weak memory
119 * models to ensure the LF LIFO element reads are properly
120 * ordered with respect to the head pointer read.
124 rte_prefetch0(old_head.top);
128 /* Traverse the list to find the new head. A next pointer will
129 * either point to another element or NULL; if a thread
130 * encounters a pointer that has already been popped, the CAS
133 for (i = 0; i < num && tmp != NULL; i++) {
134 rte_prefetch0(tmp->next);
136 obj_table[i] = tmp->data;
142 /* If NULL was encountered, the list was modified while
143 * traversing it. Retry.
149 new_head.cnt = old_head.cnt + 1;
151 /* old_head is updated on failure */
152 success = rte_atomic128_cmp_exchange(
153 (rte_int128_t *)&list->head,
154 (rte_int128_t *)&old_head,
155 (rte_int128_t *)&new_head,
158 } while (success == 0);
164 #endif /* _RTE_STACK_LF_GENERIC_H_ */