New upstream version 18.11-rc2

[deb_dpdk.git] / lib / librte_ring / rte_ring_c11_mem.h

diff --git a/lib/librte_ring/rte_ring_c11_mem.h b/lib/librte_ring/rte_ring_c11_mem.h
index 94df3c4..7bc74a4 100644 (file)
--- a/lib/librte_ring/rte_ring_c11_mem.h
+++ b/lib/librte_ring/rte_ring_c11_mem.h
@@ -57,23 +57,27 @@ __rte_ring_move_prod_head(struct rte_ring *r, unsigned int is_sp,
                uint32_t *free_entries)
 {
        const uint32_t capacity = r->capacity;
+       uint32_t cons_tail;
        unsigned int max = n;
        int success;
 
+       *old_head = __atomic_load_n(&r->prod.head, __ATOMIC_ACQUIRE);
        do {
                /* Reset n to the initial burst count */
                n = max;
 
-               *old_head = __atomic_load_n(&r->prod.head,
+               /* load-acquire synchronize with store-release of ht->tail
+                * in update_tail.
+                */
+               cons_tail = __atomic_load_n(&r->cons.tail,
                                        __ATOMIC_ACQUIRE);
 
-               /*
-                *  The subtraction is done between two unsigned 32bits value
+               /* The subtraction is done between two unsigned 32bits value
                 * (the result is always modulo 32 bits even if we have
                 * *old_head > cons_tail). So 'free_entries' is always between 0
                 * and capacity (which is < size).
                 */
-               *free_entries = (capacity + r->cons.tail - *old_head);
+               *free_entries = (capacity + cons_tail - *old_head);
 
                /* check that we have enough room in ring */
                if (unlikely(n > *free_entries))
@@ -87,6 +91,7 @@ __rte_ring_move_prod_head(struct rte_ring *r, unsigned int is_sp,
                if (is_sp)
                        r->prod.head = *new_head, success = 1;
                else
+                       /* on failure, *old_head is updated */
                        success = __atomic_compare_exchange_n(&r->prod.head,
                                        old_head, *new_head,
                                        0, __ATOMIC_ACQUIRE,
@@ -125,13 +130,19 @@ __rte_ring_move_cons_head(struct rte_ring *r, int is_sc,
                uint32_t *entries)
 {
        unsigned int max = n;
+       uint32_t prod_tail;
        int success;
 
        /* move cons.head atomically */
+       *old_head = __atomic_load_n(&r->cons.head, __ATOMIC_ACQUIRE);
        do {
                /* Restore n as it may change every loop */
                n = max;
-               *old_head = __atomic_load_n(&r->cons.head,
+
+               /* this load-acquire synchronize with store-release of ht->tail
+                * in update_tail.
+                */
+               prod_tail = __atomic_load_n(&r->prod.tail,
                                        __ATOMIC_ACQUIRE);
 
                /* The subtraction is done between two unsigned 32bits value
@@ -139,7 +150,7 @@ __rte_ring_move_cons_head(struct rte_ring *r, int is_sc,
                 * cons_head > prod_tail). So 'entries' is always between 0
                 * and size(ring)-1.
                 */
-               *entries = (r->prod.tail - *old_head);
+               *entries = (prod_tail - *old_head);
 
                /* Set the actual entries for dequeue */
                if (n > *entries)
@@ -152,6 +163,7 @@ __rte_ring_move_cons_head(struct rte_ring *r, int is_sc,
                if (is_sc)
                        r->cons.head = *new_head, success = 1;
                else
+                       /* on failure, *old_head will be updated */
                        success = __atomic_compare_exchange_n(&r->cons.head,
                                                        old_head, *new_head,
                                                        0, __ATOMIC_ACQUIRE,