[v3,1/5] ring: add 64-bit headtail structure
Checks
Commit Message
64-bit head and tail index widths greatly increases the time it takes for
them to wrap-around (with current CPU speeds, it won't happen within the
author's lifetime). This is important in 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
non-blocking ring implementation. Using a 64-bit index makes the
possibility of this occurring effectively zero.
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.eads@intel.com>
---
lib/librte_eventdev/rte_event_ring.h | 2 +-
lib/librte_ring/Makefile | 3 +-
lib/librte_ring/rte_ring.h | 24 +++++-
lib/librte_ring/rte_ring_generic_64.h | 152 ++++++++++++++++++++++++++++++++++
4 files changed, 176 insertions(+), 5 deletions(-)
create mode 100644 lib/librte_ring/rte_ring_generic_64.h
@@ -1,5 +1,5 @@
/* SPDX-License-Identifier: BSD-3-Clause
- * Copyright(c) 2016-2017 Intel Corporation
+ * Copyright(c) 2016-2019 Intel Corporation
*/
/**
@@ -19,6 +19,7 @@ SRCS-$(CONFIG_RTE_LIBRTE_RING) := rte_ring.c
# install includes
SYMLINK-$(CONFIG_RTE_LIBRTE_RING)-include := rte_ring.h \
rte_ring_generic.h \
- rte_ring_c11_mem.h
+ rte_ring_c11_mem.h \
+ rte_ring_generic_64.h
include $(RTE_SDK)/mk/rte.lib.mk
@@ -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 kmacy@freebsd.org
* All rights reserved.
* Derived from FreeBSD's bufring.h
@@ -70,6 +70,15 @@ struct rte_ring_headtail {
uint32_t single; /**< True if single prod/cons */
};
+/* 64-bit version of rte_ring_headtail, for use by rings that need to avoid
+ * head/tail wrap-around.
+ */
+struct rte_ring_headtail_64 {
+ volatile uint64_t head; /**< Prod/consumer head. */
+ volatile uint64_t tail; /**< Prod/consumer tail. */
+ uint32_t single; /**< True if single prod/cons */
+};
+
/**
* An RTE ring structure.
*
@@ -97,11 +106,19 @@ 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_64 prod_64 __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_64 cons_64 __rte_cache_aligned;
+ };
char pad2 __rte_cache_aligned; /**< empty cache line */
};
@@ -312,6 +329,7 @@ void rte_ring_dump(FILE *f, const struct rte_ring *r);
#else
#include "rte_ring_generic.h"
#endif
+#include "rte_ring_generic_64.h"
/**
* @internal Enqueue several objects on the ring
new file mode 100644
@@ -0,0 +1,152 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ *
+ * Copyright (c) 2010-2019 Intel Corporation
+ * Copyright (c) 2007-2009 Kip Macy kmacy@freebsd.org
+ * All rights reserved.
+ * Derived from FreeBSD's bufring.h
+ * Used as BSD-3 Licensed with permission from Kip Macy.
+ */
+
+#ifndef _RTE_RING_GENERIC_64_H_
+#define _RTE_RING_GENERIC_64_H_
+
+/**
+ * @internal This function updates the producer head for enqueue using
+ * 64-bit 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_64(struct rte_ring *r, unsigned int is_sp,
+ unsigned int n, enum rte_ring_queue_behavior behavior,
+ uint64_t *old_head, uint64_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_64.head;
+
+ /* add rmb barrier to avoid load/load reorder in weak
+ * memory model. It is noop on x86
+ */
+ rte_smp_rmb();
+
+ /*
+ * The subtraction is done between two unsigned 64bits value
+ * (the result is always modulo 64 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_64.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_64.head = *new_head, success = 1;
+ else
+ success = rte_atomic64_cmpset(&r->prod_64.head,
+ *old_head, *new_head);
+ } while (unlikely(success == 0));
+ return n;
+}
+
+/**
+ * @internal This function updates the consumer head for dequeue using
+ * 64-bit 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_64(struct rte_ring *r, unsigned int is_sc,
+ unsigned int n, enum rte_ring_queue_behavior behavior,
+ uint64_t *old_head, uint64_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_64.head;
+
+ /* add rmb barrier to avoid load/load reorder in weak
+ * memory model. It is noop on x86
+ */
+ rte_smp_rmb();
+
+ /* The subtraction is done between two unsigned 64bits value
+ * (the result is always modulo 64 bits even if we have
+ * cons_head > prod_tail). So 'entries' is always between 0
+ * and size(ring)-1.
+ */
+ *entries = (r->prod_64.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_64.head = *new_head, success = 1;
+ else
+ success = rte_atomic64_cmpset(&r->cons_64.head,
+ *old_head, *new_head);
+ } while (unlikely(success == 0));
+ return n;
+}
+
+#endif /* _RTE_RING_GENERIC_64_H_ */