net/intel: do not bypass mbuf lib for buffer fast-free

Freeing mbufs directly into the mempool meant that mbuf instrumentation,
including mbuf history marking, was omitted.  The mbufs are now freed
via the rte_mbuf_raw_free_bulk() function instead.

Added a static_assert to ensure that type casting the array of struct
ci_tx_entry_vec to an array of rte_mbuf pointers remains sound.

Performance note:
  The (n & 31) condition was not removed.  For the default tx_rs_thresh
  value (32), the condition will be true.  And due to inlining, the
  rte_mbuf_raw_free_bulk() ends up in an rte_memcpy(), where the
  optimizer takes advantage of knowing that the lower bits are not set.
  This should compensate somewhat for removing the handcoded
  optimization of copying in chunks of 32 mbufs.

Signed-off-by: Morten Brørup <mb@smartsharesystems.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>
Tested-by: Bruce Richardson <bruce.richardson@intel.com>

Author: MortenBroerup

drivers/net/intel/common/tx.h

@@ -279,42 +279,12 @@ ci_tx_free_bufs_vec(struct ci_tx_queue *txq, ci_desc_done_fn desc_done, bool ctx
 			(txq->fast_free_mp = txep[0].mbuf->pool);
 
 	if (mp != NULL && (n & 31) == 0) {
-		void **cache_objs;
-		struct rte_mempool_cache *cache = rte_mempool_default_cache(mp, rte_lcore_id());
-
-		if (cache == NULL)
-			goto normal;
-
-		cache_objs = &cache->objs[cache->len];
-
-		if (n > RTE_MEMPOOL_CACHE_MAX_SIZE) {
-			rte_mempool_ops_enqueue_bulk(mp, (void *)txep, n);
-			goto done;
-		}
-
-		/* The cache follows the following algorithm
-		 *   1. Add the objects to the cache
-		 *   2. Anything greater than the cache min value (if it
-		 *   crosses the cache flush threshold) is flushed to the ring.
-		 */
-		/* Add elements back into the cache */
-		uint32_t copied = 0;
-		/* n is multiple of 32 */
-		while (copied < n) {
-			memcpy(&cache_objs[copied], &txep[copied], 32 * sizeof(void *));
-			copied += 32;
-		}
-		cache->len += n;
-
-		if (cache->len >= cache->flushthresh) {
-			rte_mempool_ops_enqueue_bulk(mp, &cache->objs[cache->size],
-					cache->len - cache->size);
-			cache->len = cache->size;
-		}
+		static_assert(sizeof(*txep) == sizeof(struct rte_mbuf *),
+				"txep array is not similar to an array of rte_mbuf pointers");
+		rte_mbuf_raw_free_bulk(mp, (void *)txep, n);
 		goto done;
 	}
 
-normal:
 	m = rte_pktmbuf_prefree_seg(txep[0].mbuf);
 	if (likely(m)) {
 		free[0] = m;