[PATCH v2] mempool: remove cache flush threshold field

[Morten Brørup]

Removed the mempool cache flush threshold field (``flushthresh``),
which was obsolete and marked for removal.

Reduced the size of the mempool cache objects array; it was double the
required size.

Also fixed a couple of commments.

The sxe2 driver was updated to use the ``size`` field instead of the
``flushthresh`` field; it contains the same value.

Signed-off-by: Morten Brørup <mb at smartsharesystems.com>
Acked-by: Andrew Rybchenko <andrew.rybchenko at oktetlabs.ru>
---
v2:
* Fixed typo in commit message.
* Release notes: No need to mention added cache guard. (AI)
* Release notes: Added note about flushthresh removal
  under removed items. (AI)
* Added note about 16-byte alignment of stats. (AI)
---
 doc/guides/rel_notes/release_26_11.rst  |  6 ++++++
 drivers/net/sxe2/sxe2_txrx_vec_avx512.c |  2 +-
 lib/mempool/mempool_trace.h             |  1 -
 lib/mempool/rte_mempool.c               |  8 ++------
 lib/mempool/rte_mempool.h               | 16 +++++-----------
 5 files changed, 14 insertions(+), 19 deletions(-)

diff --git a/doc/guides/rel_notes/release_26_11.rst b/doc/guides/rel_notes/release_26_11.rst
index 938617ca75..1083bc56b4 100644
--- a/doc/guides/rel_notes/release_26_11.rst
+++ b/doc/guides/rel_notes/release_26_11.rst
@@ -68,6 +68,8 @@ Removed Items
    Also, make sure to start the actual text at the margin.
    =======================================================
 
+* mempool: The obsolete ``flushthresh`` field was removed from the ``rte_mempool_cache`` structure.
+
 
 API Changes
 -----------
@@ -100,6 +102,10 @@ ABI Changes
    Also, make sure to start the actual text at the margin.
    =======================================================
 
+* mempool: The ``rte_mempool_cache`` structure was updated as follows:
+  - The obsolete ``flushthresh`` field was removed.
+  - The size of the ``objs`` array was reduced from ``RTE_MEMPOOL_CACHE_MAX_SIZE`` * 2 to ``RTE_MEMPOOL_CACHE_MAX_SIZE``.
+
 
 Known Issues
 ------------
diff --git a/drivers/net/sxe2/sxe2_txrx_vec_avx512.c b/drivers/net/sxe2/sxe2_txrx_vec_avx512.c
index a830c7a33b..2e680f4027 100644
--- a/drivers/net/sxe2/sxe2_txrx_vec_avx512.c
+++ b/drivers/net/sxe2/sxe2_txrx_vec_avx512.c
@@ -67,7 +67,7 @@ static __rte_always_inline int32_t sxe2_tx_bufs_free_vec_avx512(struct sxe2_tx_q
 		}
 		cache->len += rs_thresh;
 
-		if (cache->len >= cache->flushthresh) {
+		if (cache->len >= cache->size) {
 			(void)rte_mempool_ops_enqueue_bulk(mp,
 					&cache->objs[cache->size], cache->len - cache->size);
 			cache->len = cache->size;
diff --git a/lib/mempool/mempool_trace.h b/lib/mempool/mempool_trace.h
index 23cda1473c..60e47cf67b 100644
--- a/lib/mempool/mempool_trace.h
+++ b/lib/mempool/mempool_trace.h
@@ -119,7 +119,6 @@ RTE_TRACE_POINT(
 	rte_trace_point_emit_i32(socket_id);
 	rte_trace_point_emit_ptr(cache);
 	rte_trace_point_emit_u32(cache->len);
-	rte_trace_point_emit_u32(cache->flushthresh);
 )
 
 RTE_TRACE_POINT(
diff --git a/lib/mempool/rte_mempool.c b/lib/mempool/rte_mempool.c
index 817e2b8dc1..09660e89ac 100644
--- a/lib/mempool/rte_mempool.c
+++ b/lib/mempool/rte_mempool.c
@@ -753,7 +753,6 @@ static void
 mempool_cache_init(struct rte_mempool_cache *cache, uint32_t size)
 {
 	cache->size = size;
-	cache->flushthresh = size; /* Obsolete; for API/ABI compatibility purposes only */
 	cache->len = 0;
 }
 
@@ -1197,6 +1196,7 @@ mempool_obj_audit(struct rte_mempool *mp, __rte_unused void *opaque,
 	RTE_MEMPOOL_CHECK_COOKIES(mp, &obj, 1, 2);
 }
 
+/* check cookies before and after objects */
 static void
 mempool_audit_cookies(struct rte_mempool *mp)
 {
@@ -1213,11 +1213,10 @@ mempool_audit_cookies(struct rte_mempool *mp)
 #define mempool_audit_cookies(mp) do {} while(0)
 #endif
 
-/* check cookies before and after objects */
+/* check cache size consistency */
 static void
 mempool_audit_cache(const struct rte_mempool *mp)
 {
-	/* check cache size consistency */
 	unsigned lcore_id;
 
 	if (mp->cache_size == 0)
@@ -1241,9 +1240,6 @@ rte_mempool_audit(struct rte_mempool *mp)
 {
 	mempool_audit_cache(mp);
 	mempool_audit_cookies(mp);
-
-	/* For case where mempool DEBUG is not set, and cache size is 0 */
-	RTE_SET_USED(mp);
 }
 
 /* dump the status of the mempool on the console */
diff --git a/lib/mempool/rte_mempool.h b/lib/mempool/rte_mempool.h
index 50d958c7c6..2fa70812d5 100644
--- a/lib/mempool/rte_mempool.h
+++ b/lib/mempool/rte_mempool.h
@@ -89,14 +89,14 @@ struct __rte_cache_aligned rte_mempool_debug_stats {
  */
 struct __rte_cache_aligned rte_mempool_cache {
 	uint32_t size;	      /**< Size of the cache */
-	uint32_t flushthresh; /**< Obsolete; for API/ABI compatibility purposes only */
 	uint32_t len;	      /**< Current cache count */
 #ifdef RTE_LIBRTE_MEMPOOL_STATS
-	uint32_t unused;
 	/*
 	 * Alternative location for the most frequently updated mempool statistics (per-lcore),
 	 * providing faster update access when using a mempool cache.
+	 * Note: 16-byte aligned for optimal SIMD access, when updating pairs of counters.
 	 */
+	alignas(16)
 	struct {
 		uint64_t put_bulk;          /**< Number of puts. */
 		uint64_t put_objs;          /**< Number of objects successfully put. */
@@ -104,15 +104,9 @@ struct __rte_cache_aligned rte_mempool_cache {
 		uint64_t get_success_objs;  /**< Objects successfully allocated. */
 	} stats;                        /**< Statistics */
 #endif
-	/**
-	 * Cache objects
-	 *
-	 * Note:
-	 * Cache is allocated at double size for API/ABI compatibility purposes only.
-	 * When reducing its size at an API/ABI breaking release,
-	 * remember to add a cache guard after it.
-	 */
-	alignas(RTE_CACHE_LINE_SIZE) void *objs[RTE_MEMPOOL_CACHE_MAX_SIZE * 2];
+	/** Cache objects */
+	alignas(RTE_CACHE_LINE_SIZE) void *objs[RTE_MEMPOOL_CACHE_MAX_SIZE];
+	RTE_CACHE_GUARD;
 };
 
 /**
-- 
2.43.0