[PATCH V2] net/memif: fix extra mbuf refcnt update in zero copy Tx

[Wathsala Vithanage <wathsala.vithanage@arm.com>]

The refcnt update of stored mbufs in memif driver is redundant since
those mbufs are only freed in eth_memif_tx_zc(). No other place can
free those stored mbufs quietly. By removing this redundant update
single core dpdk memif performance can be improved by 7.5%.

testpmd stats on Arm Neoverse N1 (Ampere Altra)
+-----------------------------+-----------------------+
|        | With refcnt update | Without refcnt update |
+--------+--------------------+-----------------------+
| Rx-pps |      2748851       |         2955487       |
+--------+--------------------+-----------------------+
| Tx-pps |      2748812       |         2955436       |
+--------+--------------------+-----------------------+

Fixes: 43b815d88188 ("net/memif: support zero-copy slave")
Cc: jgrajcia@cisco.com

Signed-off-by: Liangxing Wang <liangxing.wang@arm.com>
Signed-off-by: Wathsala Vithanage <wathsala.vithanage@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
---
 .mailmap                          | 2 ++
 drivers/net/memif/rte_eth_memif.c | 6 ------
 2 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/.mailmap b/.mailmap
index de339562f4..00a642fcc3 100644
--- a/.mailmap
+++ b/.mailmap
@@ -791,6 +791,7 @@ Liang Ma <liangma@bytedance.com> <liangma@liangbit.com> <liang.j.ma@intel.com>
 Liang-Min Larry Wang <liang-min.wang@intel.com>
 Liang Xu <liang.xu@cinfotech.cn>
 Liang Zhang <zhangliang@bigo.sg>
+Liangxing Wang <liangxing.wang@arm.com>
 Li Feng <fengli@smartx.com>
 Li Han <han.li1@zte.com.cn>
 Lihong Ma <lihongx.ma@intel.com>
@@ -1506,6 +1507,7 @@ Vlad Zolotarov <vladz@cloudius-systems.com>
 Vlastimil Kosar <kosar@rehivetech.com>
 Volodymyr Fialko <vfialko@marvell.com>
 Vu Pham <vuhuong@mellanox.com>
+Wathsala Vithanage <wathsala.vithanage@arm.com>
 Wajeeh Atrash <atrwajee@amazon.com>
 Walter Heymans <walter.heymans@corigine.com>
 Wang Sheng-Hui <shhuiw@gmail.com>
diff --git a/drivers/net/memif/rte_eth_memif.c b/drivers/net/memif/rte_eth_memif.c
index 7cc8c0da91..962d390b90 100644
--- a/drivers/net/memif/rte_eth_memif.c
+++ b/drivers/net/memif/rte_eth_memif.c
@@ -265,8 +265,6 @@ memif_free_stored_mbufs(struct pmd_process_private *proc_private, struct memif_q
 	cur_tail = __atomic_load_n(&ring->tail, __ATOMIC_ACQUIRE);
 	while (mq->last_tail != cur_tail) {
 		RTE_MBUF_PREFETCH_TO_FREE(mq->buffers[(mq->last_tail + 1) & mask]);
-		/* Decrement refcnt and free mbuf. (current segment) */
-		rte_mbuf_refcnt_update(mq->buffers[mq->last_tail & mask], -1);
 		rte_pktmbuf_free_seg(mq->buffers[mq->last_tail & mask]);
 		mq->last_tail++;
 	}
@@ -825,10 +823,6 @@ memif_tx_one_zc(struct pmd_process_private *proc_private, struct memif_queue *mq
 next_in_chain:
 	/* store pointer to mbuf to free it later */
 	mq->buffers[slot & mask] = mbuf;
-	/* Increment refcnt to make sure the buffer is not freed before server
-	 * receives it. (current segment)
-	 */
-	rte_mbuf_refcnt_update(mbuf, 1);
 	/* populate descriptor */
 	d0 = &ring->desc[slot & mask];
 	d0->length = rte_pktmbuf_data_len(mbuf);
-- 
2.25.1