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From: lilinzhe <slayercat.subscription@gmail.com>
To: dev@dpdk.org
Cc: =?UTF-8?q?=E6=9D=8E=E6=9E=97=E5=93=B2?= <lilinzhe@ijinshan.com>
Date: Fri, 2 Sep 2016 13:25:06 +0800
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Subject: [dpdk-dev] [PATCH] mbuf: fix atomic refcnt update synchronization
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From: 李林哲 <lilinzhe@ijinshan.com>
chagne atomic ref update to always call atomic_add
when mbuf is allocated by cpu1 and freed by cpu2. cpu1 cache may not be updated by such a set operation.
causes refcnt reads incorrect values.
---
lib/librte_mbuf/rte_mbuf.h | 16 ++++++----------
1 file changed, 6 insertions(+), 10 deletions(-)
diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index 7ea66ed..63e6588 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -786,7 +786,7 @@ struct rte_mbuf {
*/
union {
rte_atomic16_t refcnt_atomic; /**< Atomically accessed refcnt */
- uint16_t refcnt; /**< Non-atomically accessed refcnt */
+ volatile uint16_t refcnt; /**< Non-atomically accessed refcnt */
};
uint8_t nb_segs; /**< Number of segments. */
uint8_t port; /**< Input port. */
@@ -1060,16 +1060,12 @@ static inline uint16_t
rte_mbuf_refcnt_update(struct rte_mbuf *m, int16_t value)
{
/*
- * The atomic_add is an expensive operation, so we don't want to
- * call it in the case where we know we are the uniq holder of
- * this mbuf (i.e. ref_cnt == 1). Otherwise, an atomic
- * operation has to be used because concurrent accesses on the
- * reference counter can occur.
+ * This shell always call atomic_add
+ *
+ * when mbuf is allocated by cpu1 and freed by cpu2. cpu1 cache may not be updated by such a set operation.
+ * causes refcnt reads incorrect values
+ *
*/
- if (likely(rte_mbuf_refcnt_read(m) == 1)) {
- rte_mbuf_refcnt_set(m, 1 + value);
- return 1 + value;
- }
return (uint16_t)(rte_atomic16_add_return(&m->refcnt_atomic, value));
}
--
2.7.0.rc2