[PATCH] mempool: simplify get objects

["Morten Brørup" <mb@smartsharesystems.com>]

Removed explicit test for build time constant request size,
and added comment that the compiler loop unrolls when request size is
build time constant, to improve source code readability.

Also, when putting objects, the compiler does not know if calling
rte_mempool_ops_enqueue_bulk() modifies cache->len, so load it before the
call, so it doesn't have to be loaded again after the call.

Signed-off-by: Morten Brørup <mb@smartsharesystems.com>
---
 lib/mempool/rte_mempool.h | 38 ++++++++++----------------------------
 1 file changed, 10 insertions(+), 28 deletions(-)

diff --git a/lib/mempool/rte_mempool.h b/lib/mempool/rte_mempool.h
index aedc100964..61b415e336 100644
--- a/lib/mempool/rte_mempool.h
+++ b/lib/mempool/rte_mempool.h
@@ -1410,8 +1410,9 @@ rte_mempool_do_generic_put(struct rte_mempool *mp, void * const *obj_table,
 		 * Flush the cache to make room for the objects.
 		 */
 		cache_objs = &cache->objs[0];
-		rte_mempool_ops_enqueue_bulk(mp, cache_objs, cache->len);
+		const uint32_t len = cache->len;
 		cache->len = n;
+		rte_mempool_ops_enqueue_bulk(mp, cache_objs, len);
 	} else {
 		/* The request itself is too big for the cache. */
 		goto driver_enqueue_stats_incremented;
@@ -1531,11 +1532,11 @@ rte_mempool_do_generic_get(struct rte_mempool *mp, void **obj_table,
 	cache_objs = &cache->objs[cache->len];
 
 	__rte_assume(cache->len <= RTE_MEMPOOL_CACHE_MAX_SIZE * 2);
-	if (__rte_constant(n) && n <= cache->len) {
+	if (likely(n <= cache->len)) {
 		/*
-		 * The request size is known at build time, and
-		 * the entire request can be satisfied from the cache,
-		 * so let the compiler unroll the fixed length copy loop.
+		 * The entire request can be satisfied from the cache.
+		 * If the request size is known at build time,
+		 * the compiler unrolls the fixed length copy loop.
 		 */
 		cache->len -= n;
 		for (index = 0; index < n; index++)
@@ -1547,31 +1548,13 @@ rte_mempool_do_generic_get(struct rte_mempool *mp, void **obj_table,
 		return 0;
 	}
 
-	/*
-	 * Use the cache as much as we have to return hot objects first.
-	 * If the request size 'n' is known at build time, the above comparison
-	 * ensures that n > cache->len here, so omit RTE_MIN().
-	 */
-	len = __rte_constant(n) ? cache->len : RTE_MIN(n, cache->len);
-	cache->len -= len;
+	/* Use the cache as much as we have to return hot objects first. */
+	len = cache->len;
 	remaining = n - len;
+	cache->len = 0;
 	for (index = 0; index < len; index++)
 		*obj_table++ = *--cache_objs;
 
-	/*
-	 * If the request size 'n' is known at build time, the case
-	 * where the entire request can be satisfied from the cache
-	 * has already been handled above, so omit handling it here.
-	 */
-	if (!__rte_constant(n) && likely(remaining == 0)) {
-		/* The entire request is satisfied from the cache. */
-
-		RTE_MEMPOOL_CACHE_STAT_ADD(cache, get_success_bulk, 1);
-		RTE_MEMPOOL_CACHE_STAT_ADD(cache, get_success_objs, n);
-
-		return 0;
-	}
-
 	/* Dequeue below would overflow mem allocated for cache? */
 	if (unlikely(remaining > RTE_MEMPOOL_CACHE_MAX_SIZE))
 		goto driver_dequeue;
@@ -1592,11 +1575,10 @@ rte_mempool_do_generic_get(struct rte_mempool *mp, void **obj_table,
 	__rte_assume(cache->size <= RTE_MEMPOOL_CACHE_MAX_SIZE);
 	__rte_assume(remaining <= RTE_MEMPOOL_CACHE_MAX_SIZE);
 	cache_objs = &cache->objs[cache->size + remaining];
+	cache->len = cache->size;
 	for (index = 0; index < remaining; index++)
 		*obj_table++ = *--cache_objs;
 
-	cache->len = cache->size;
-
 	RTE_MEMPOOL_CACHE_STAT_ADD(cache, get_success_bulk, 1);
 	RTE_MEMPOOL_CACHE_STAT_ADD(cache, get_success_objs, n);
 
-- 
2.43.0