Hi, Beilei

Thanks for your comments, please see below.

-----邮件原件-----
发件人: Xing, Beilei [off-list ref]
发送时间: 2021年6月22日 14:08
收件人: Feifei Wang [off-list ref]
抄送: dev@dpdk.org; nd [off-list ref]; Ruifeng Wang
[off-list ref]
主题: RE: [PATCH v1 1/2] net/i40e: improve performance for scalar Tx

quoted

-----Original Message-----
From: Feifei Wang <redacted>
Sent: Thursday, May 27, 2021 4:17 PM
To: Xing, Beilei <redacted>
Cc: dev@dpdk.org; nd@arm.com; Feifei Wang <redacted>;
Ruifeng Wang [off-list ref]
Subject: [PATCH v1 1/2] net/i40e: improve performance for scalar Tx

For i40e scalar Tx path, if implement FAST_FREE_MBUF mode, it means
per- queue all mbufs come from the same mempool and have refcnt = 1.

Thus we can use bulk free of the buffers when mbuf fast free mode is
enabled.

For scalar path in arm platform:
In n1sdp, performance is improved by 7.8%; In thunderx2, performance
is improved by 6.7%.

For scalar path in x86 platform,
performance is improved by 6%.

Suggested-by: Ruifeng Wang <redacted>
Signed-off-by: Feifei Wang <redacted>
---
 drivers/net/i40e/i40e_rxtx.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/i40e/i40e_rxtx.c

b/drivers/net/i40e/i40e_rxtx.c index
6c58decece..fe7b20f750 100644

--- a/drivers/net/i40e/i40e_rxtx.c
+++ b/drivers/net/i40e/i40e_rxtx.c

@@ -1295,6 +1295,7 @@ i40e_tx_free_bufs(struct i40e_tx_queue *txq)  {
 	struct i40e_tx_entry *txep;
 	uint16_t i;
+	struct rte_mbuf *free[RTE_I40E_TX_MAX_FREE_BUF_SZ];

 	if ((txq->tx_ring[txq->tx_next_dd].cmd_type_offset_bsz &

	rte_cpu_to_le_64(I40E_TXD_QW1_DTYPE_MASK)) != @@ -1308,9
+1309,11

quoted

@@ i40e_tx_free_bufs(struct i40e_tx_queue *txq)

 	if (txq->offloads & DEV_TX_OFFLOAD_MBUF_FAST_FREE) {
 		for (i = 0; i < txq->tx_rs_thresh; ++i, ++txep) {
-			rte_mempool_put(txep->mbuf->pool, txep->mbuf);
+			free[i] = txep->mbuf;

The tx_rs_thresh can be 'nb_desc - 3', so if tx_rs_thres >
RTE_I40E_TX_MAX_FREE_BUF_SZ, there'll be out of bounds, right?

Actually tx_rs_thresh  <=  tx__free_thresh  <  nb_desc - 3 (i40e_dev_tx_queue_setup).
However, I don't know how it affects the relationship between tx_rs_thresh and
RTE_I40E_TX_MAX_FREE_BUF_SZ.

Furthermore, I think you are right that tx_rs_thres can be greater than
RTE_I40E_TX_MAX_FREE_BUF_SZ in tx_simple_mode (i40e_set_tx_function_flag).

Thus, in scalar path, we can change like:
---------------------------------------------------------------------------------------------------------------
int n = txq->tx_rs_thresh;
int32_t i = 0, j = 0;
const int32_t k = RTE_ALIGN_FLOOR(n, RTE_I40E_TX_MAX_FREE_BUF_SZ);
const int32_t m = n % RTE_I40E_TX_MAX_FREE_BUF_SZ;
struct rte_mbuf *free[RTE_I40E_TX_MAX_FREE_BUF_SZ];

For FAST_FREE_MODE:
	
if (k) {
	for (j = 0; j != k - RTE_I40E_TX_MAX_FREE_BUF_SZ;
			j += RTE_I40E_TX_MAX_FREE_BUF_SZ) {
		for (i = 0; i <RTE_I40E_TX_MAX_FREE_BUF_SZ; ++i, ++txep) {
			free[i] = txep->mbuf;
			txep->mbuf = NULL;
		}
		rte_mempool_put_bulk(free[0]->pool, (void **)free,
					RTE_I40E_TX_MAX_FREE_BUF_SZ);
	}
} else {
	for (i = 0; i < m; ++i, ++txep) {
		free[i] = txep->mbuf;
		txep->mbuf = NULL;
	}
	rte_mempool_put_bulk(free[0]->pool, (void **)free, m);
}
---------------------------------------------------------------------------------------------------------------

Best Regards
Feifei