For 64-bit systems, at current CPU speeds, 64-bit head and tail indexes
will not wrap-around within the author's lifetime. This is important to
avoiding the ABA problem -- in which a thread mistakes reading the same
tail index in two accesses to mean that the ring was not modified in the
intervening time -- in the upcoming lock-free ring implementation. Using a
64-bit index makes the possibility of this occurring effectively zero. This
commit uses pointer-width indexes so the lock-free ring can support 32-bit
systems as well.
This commit places the new producer and consumer structures in the same
location in struct rte_ring as their 32-bit counterparts. Since the 32-bit
versions are padded out to a cache line, there is space for the new
structure without affecting the layout of struct rte_ring. Thus, the ABI is
preserved.
Signed-off-by: Gage Eads <gage.e...@intel.com>
---
lib/librte_ring/rte_ring.h | 21 +++++-
lib/librte_ring/rte_ring_c11_mem.h | 143 +++++++++++++++++++++++++++++++++++++
lib/librte_ring/rte_ring_generic.h | 130 +++++++++++++++++++++++++++++++++
3 files changed, 291 insertions(+), 3 deletions(-)
diff --git a/lib/librte_ring/rte_ring.h b/lib/librte_ring/rte_ring.h
index af5444a9f..c78db6916 100644
--- a/lib/librte_ring/rte_ring.h
+++ b/lib/librte_ring/rte_ring.h
@@ -1,6 +1,6 @@
/* SPDX-License-Identifier: BSD-3-Clause
*
- * Copyright (c) 2010-2017 Intel Corporation
+ * Copyright (c) 2010-2019 Intel Corporation
* Copyright (c) 2007-2009 Kip Macy km...@freebsd.org
* All rights reserved.
* Derived from FreeBSD's bufring.h
@@ -70,6 +70,13 @@ struct rte_ring_headtail {
uint32_t single; /**< True if single prod/cons */
};
+/* Structure to hold a pair of pointer-sized head/tail values and metadata */
+struct rte_ring_headtail_ptr {
+ volatile uintptr_t head; /**< Prod/consumer head. */
+ volatile uintptr_t tail; /**< Prod/consumer tail. */
+ uint32_t single; /**< True if single prod/cons */
+};
+
/**
* An RTE ring structure.
*
@@ -97,11 +104,19 @@ struct rte_ring {
char pad0 __rte_cache_aligned; /**< empty cache line */
/** Ring producer status. */
- struct rte_ring_headtail prod __rte_cache_aligned;
+ RTE_STD_C11
+ union {
+ struct rte_ring_headtail prod __rte_cache_aligned;
+ struct rte_ring_headtail_ptr prod_ptr __rte_cache_aligned;
+ };
char pad1 __rte_cache_aligned; /**< empty cache line */
/** Ring consumer status. */
- struct rte_ring_headtail cons __rte_cache_aligned;
+ RTE_STD_C11
+ union {
+ struct rte_ring_headtail cons __rte_cache_aligned;
+ struct rte_ring_headtail_ptr cons_ptr __rte_cache_aligned;
+ };
char pad2 __rte_cache_aligned; /**< empty cache line */
};
diff --git a/lib/librte_ring/rte_ring_c11_mem.h
b/lib/librte_ring/rte_ring_c11_mem.h
index 0fb73a337..545caf257 100644
--- a/lib/librte_ring/rte_ring_c11_mem.h
+++ b/lib/librte_ring/rte_ring_c11_mem.h
@@ -178,4 +178,147 @@ __rte_ring_move_cons_head(struct rte_ring *r, int is_sc,
return n;
}
+/**
+ * @internal This function updates the producer head for enqueue using
+ * pointer-sized head/tail values.
+ *
+ * @param r
+ * A pointer to the ring structure
+ * @param is_sp
+ * Indicates whether multi-producer path is needed or not
+ * @param n
+ * The number of elements we will want to enqueue, i.e. how far should the
+ * head be moved
+ * @param behavior
+ * RTE_RING_QUEUE_FIXED: Enqueue a fixed number of items from a ring
+ * RTE_RING_QUEUE_VARIABLE: Enqueue as many items as possible from ring
+ * @param old_head
+ * Returns head value as it was before the move, i.e. where enqueue starts
+ * @param new_head
+ * Returns the current/new head value i.e. where enqueue finishes
+ * @param free_entries
+ * Returns the amount of free space in the ring BEFORE head was moved
+ * @return
+ * Actual number of objects enqueued.
+ * If behavior == RTE_RING_QUEUE_FIXED, this will be 0 or n only.
+ */
+static __rte_always_inline unsigned int
+__rte_ring_move_prod_head_ptr(struct rte_ring *r, unsigned int is_sp,
+ unsigned int n, enum rte_ring_queue_behavior behavior,
+ uintptr_t *old_head, uintptr_t *new_head,
+ uint32_t *free_entries)
+{
+ const uint32_t capacity = r->capacity;
+ uintptr_t cons_tail;
+ unsigned int max = n;
+ int success;
+
+ *old_head = __atomic_load_n(&r->prod_ptr.head, __ATOMIC_RELAXED);
+ do {
+ /* Reset n to the initial burst count */
+ n = max;
+
+ /* Ensure the head is read before tail */
+ __atomic_thread_fence(__ATOMIC_ACQUIRE);
+
+ /* load-acquire synchronize with store-release of ht->tail
+ * in update_tail.
+ */
+ cons_tail = __atomic_load_n(&r->cons_ptr.tail,
+ __ATOMIC_ACQUIRE);
+
+ *free_entries = (capacity + cons_tail - *old_head);
+
+ /* check that we have enough room in ring */
+ if (unlikely(n > *free_entries))
+ n = (behavior == RTE_RING_QUEUE_FIXED) ?
+ 0 : *free_entries;
+
+ if (n == 0)
+ return 0;
+
+ *new_head = *old_head + n;
+ if (is_sp)
+ r->prod_ptr.head = *new_head, success = 1;
+ else
+ /* on failure, *old_head is updated */
+ success = __atomic_compare_exchange_n(&r->prod_ptr.head,
+ old_head, *new_head,
+ 0, __ATOMIC_RELAXED,
+ __ATOMIC_RELAXED);
+ } while (unlikely(success == 0));
+ return n;
+}
+
+/**
+ * @internal This function updates the consumer head for dequeue using
+ * pointer-sized head/tail values.
+ *
+ * @param r
+ * A pointer to the ring structure
+ * @param is_sc
+ * Indicates whether multi-consumer path is needed or not
+ * @param n
+ * The number of elements we will want to enqueue, i.e. how far should the
+ * head be moved
+ * @param behavior
+ * RTE_RING_QUEUE_FIXED: Dequeue a fixed number of items from a ring
+ * RTE_RING_QUEUE_VARIABLE: Dequeue as many items as possible from ring
+ * @param old_head
+ * Returns head value as it was before the move, i.e. where dequeue starts
+ * @param new_head
+ * Returns the current/new head value i.e. where dequeue finishes
+ * @param entries
+ * Returns the number of entries in the ring BEFORE head was moved
+ * @return
+ * - Actual number of objects dequeued.
+ * If behavior == RTE_RING_QUEUE_FIXED, this will be 0 or n only.
+ */
+static __rte_always_inline unsigned int
+__rte_ring_move_cons_head_ptr(struct rte_ring *r, unsigned int is_sc,
+ unsigned int n, enum rte_ring_queue_behavior behavior,
+ uintptr_t *old_head, uintptr_t *new_head,
+ uint32_t *entries)
+{
+ unsigned int max = n;
+ uintptr_t prod_tail;
+ int success;
+
+ /* move cons.head atomically */
+ *old_head = __atomic_load_n(&r->cons_ptr.head, __ATOMIC_RELAXED);
+ do {
+ /* Restore n as it may change every loop */
+ n = max;
+
+ /* Ensure the head is read before tail */
+ __atomic_thread_fence(__ATOMIC_ACQUIRE);
+
+ /* this load-acquire synchronize with store-release of ht->tail
+ * in update_tail.
+ */
+ prod_tail = __atomic_load_n(&r->prod_ptr.tail,
+ __ATOMIC_ACQUIRE);
+
+ *entries = (prod_tail - *old_head);
+
+ /* Set the actual entries for dequeue */
+ if (n > *entries)
+ n = (behavior == RTE_RING_QUEUE_FIXED) ? 0 : *entries;
+
+ if (unlikely(n == 0))
+ return 0;
+
+ *new_head = *old_head + n;
+ if (is_sc)
+ r->cons_ptr.head = *new_head, success = 1;
+ else
+ /* on failure, *old_head will be updated */
+ success = __atomic_compare_exchange_n(&r->cons_ptr.head,
+ old_head, *new_head,
+ 0, __ATOMIC_RELAXED,
+ __ATOMIC_RELAXED);
+ } while (unlikely(success == 0));
+ return n;
+}
+
#endif /* _RTE_RING_C11_MEM_H_ */
diff --git a/lib/librte_ring/rte_ring_generic.h
b/lib/librte_ring/rte_ring_generic.h
index ea7dbe5b9..6a0e1bbfb 100644
--- a/lib/librte_ring/rte_ring_generic.h
+++ b/lib/librte_ring/rte_ring_generic.h
@@ -167,4 +167,134 @@ __rte_ring_move_cons_head(struct rte_ring *r, unsigned
int is_sc,
return n;
}
+/**
+ * @internal This function updates the producer head for enqueue using
+ * pointer-sized head/tail values.
+ *
+ * @param r
+ * A pointer to the ring structure
+ * @param is_sp
+ * Indicates whether multi-producer path is needed or not
+ * @param n
+ * The number of elements we will want to enqueue, i.e. how far should the
+ * head be moved
+ * @param behavior
+ * RTE_RING_QUEUE_FIXED: Enqueue a fixed number of items from a ring
+ * RTE_RING_QUEUE_VARIABLE: Enqueue as many items as possible from ring
+ * @param old_head
+ * Returns head value as it was before the move, i.e. where enqueue starts
+ * @param new_head
+ * Returns the current/new head value i.e. where enqueue finishes
+ * @param free_entries
+ * Returns the amount of free space in the ring BEFORE head was moved
+ * @return
+ * Actual number of objects enqueued.
+ * If behavior == RTE_RING_QUEUE_FIXED, this will be 0 or n only.
+ */
+static __rte_always_inline unsigned int
+__rte_ring_move_prod_head_ptr(struct rte_ring *r, unsigned int is_sp,
+ unsigned int n, enum rte_ring_queue_behavior behavior,
+ uintptr_t *old_head, uintptr_t *new_head,
+ uint32_t *free_entries)
+{
+ const uint32_t capacity = r->capacity;
+ unsigned int max = n;
+ int success;
+
+ do {
+ /* Reset n to the initial burst count */
+ n = max;
+
+ *old_head = r->prod_ptr.head;
+
+ /* add rmb barrier to avoid load/load reorder in weak
+ * memory model. It is noop on x86
+ */
+ rte_smp_rmb();
+
+ *free_entries = (capacity + r->cons_ptr.tail - *old_head);
+
+ /* check that we have enough room in ring */
+ if (unlikely(n > *free_entries))
+ n = (behavior == RTE_RING_QUEUE_FIXED) ?
+ 0 : *free_entries;
+
+ if (n == 0)
+ return 0;
+
+ *new_head = *old_head + n;
+ if (is_sp)
+ r->prod_ptr.head = *new_head, success = 1;
+ else
+ success = __sync_bool_compare_and_swap(
+ &r->prod_ptr.head,
+ *old_head, *new_head);
+ } while (unlikely(success == 0));
+ return n;
+}
+
+/**
+ * @internal This function updates the consumer head for dequeue using
+ * pointer-sized head/tail values.
+ *
+ * @param r
+ * A pointer to the ring structure
+ * @param is_sc
+ * Indicates whether multi-consumer path is needed or not
+ * @param n
+ * The number of elements we will want to enqueue, i.e. how far should the
+ * head be moved
+ * @param behavior
+ * RTE_RING_QUEUE_FIXED: Dequeue a fixed number of items from a ring
+ * RTE_RING_QUEUE_VARIABLE: Dequeue as many items as possible from ring
+ * @param old_head
+ * Returns head value as it was before the move, i.e. where dequeue starts
+ * @param new_head
+ * Returns the current/new head value i.e. where dequeue finishes
+ * @param entries
+ * Returns the number of entries in the ring BEFORE head was moved
+ * @return
+ * - Actual number of objects dequeued.
+ * If behavior == RTE_RING_QUEUE_FIXED, this will be 0 or n only.
+ */
+static __rte_always_inline unsigned int
+__rte_ring_move_cons_head_ptr(struct rte_ring *r, unsigned int is_sc,
+ unsigned int n, enum rte_ring_queue_behavior behavior,
+ uintptr_t *old_head, uintptr_t *new_head,
+ uint32_t *entries)
+{
+ unsigned int max = n;
+ int success;
+
+ do {
+ /* Restore n as it may change every loop */
+ n = max;
+
+ *old_head = r->cons_ptr.head;
+
+ /* add rmb barrier to avoid load/load reorder in weak
+ * memory model. It is noop on x86
+ */
+ rte_smp_rmb();
+
+ *entries = (r->prod_ptr.tail - *old_head);
+
+ /* Set the actual entries for dequeue */
+ if (n > *entries)
+ n = (behavior == RTE_RING_QUEUE_FIXED) ? 0 : *entries;
+
+ if (unlikely(n == 0))
+ return 0;
+
+ *new_head = *old_head + n;
+ if (is_sc)
+ r->cons_ptr.head = *new_head, success = 1;
+ else
+ success = __sync_bool_compare_and_swap(
+ &r->cons_ptr.head,
+ *old_head, *new_head);
+ } while (unlikely(success == 0));
+ return n;
+}
+
#endif /* _RTE_RING_GENERIC_H_ */
--
2.13.6
