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 8 #include <rte_branch_prediction.h> 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 */ 63 success = rte_atomic128_cmp_exchange( 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 = 0; 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 old_head = list->head; 133 continue; 134 } 135 136 new_head.top = tmp; 137 new_head.cnt = old_head.cnt + 1; 138 139 /* old_head is updated on failure */ 140 success = rte_atomic128_cmp_exchange( 141 (rte_int128_t *)&list->head, 142 (rte_int128_t *)&old_head, 143 (rte_int128_t *)&new_head, 144 1, __ATOMIC_RELEASE, 145 __ATOMIC_RELAXED); 146 } while (success == 0); 147 148 return old_head.top; 149 } 150 151 #endif /* _RTE_STACK_LF_GENERIC_H_ */ 152