[PATCH v2] ring: add cache guard after ring elements table

[Morten Brørup]

Added cache guard after the table holding the ring elements, to avoid
false sharing conflicts caused by next-line hardware prefetchers when
accessing elements at the end of the ring table.

Signed-off-by: Morten Brørup <mb at smartsharesystems.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev at huawei.com>
---
v2:
* Added comment describing reason for padding. (Konstantin)
---
 lib/ring/rte_ring.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/lib/ring/rte_ring.c b/lib/ring/rte_ring.c
index f10050a1c4..10b52dc679 100644
--- a/lib/ring/rte_ring.c
+++ b/lib/ring/rte_ring.c
@@ -73,8 +73,15 @@ rte_ring_get_memsize_elem(unsigned int esize, unsigned int count)
 		return -EINVAL;
 	}
 
+	static_assert(sizeof(struct rte_ring) == RTE_CACHE_LINE_ROUNDUP(sizeof(struct rte_ring)),
+			"Size of struct rte_ring not cache line aligned");
 	sz = sizeof(struct rte_ring) + (ssize_t)count * esize;
+	/* Add padding, to guard against false sharing-like effects
+	 * on systems with a next-N-lines hardware prefetcher, when
+	 * accessing elements at the end of the ring table.
+	 */
 	sz = RTE_ALIGN(sz, RTE_CACHE_LINE_SIZE);
+	sz += RTE_CACHE_GUARD_LINES * RTE_CACHE_LINE_SIZE;
 	return sz;
 }
 
-- 
2.43.0