RE: [PATCH] examples/l3fwd: adjust Tx burst size based on Rx burst

[Konstantin Ananyev <konstantin.ananyev@huawei.com>]

> Previously, the TX burst size was fixed at 256, leading to performance
> degradation in certain scenarios.
> 
> This patch introduces logic to set the TX burst size to match the
> configured RX burst size (--burst option, default 32, max 512)
> for better efficiency.
> 
> Fixes: d5c4897ecfb2 ("examples/l3fwd: add option to set Rx burst size")
> Cc: haijie1@huawei.com
> Cc: stable@dpdk.org
> 
> Signed-off-by: Sivaprasad Tummala <sivaprasad.tummala@amd.com>
> ---
>  examples/l3fwd/l3fwd.h        |  6 +++---
>  examples/l3fwd/l3fwd_common.h | 11 +++++++----
>  examples/l3fwd/main.c         |  2 ++
>  3 files changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/examples/l3fwd/l3fwd.h b/examples/l3fwd/l3fwd.h
> index 0cce3406ee..9d7c73504b 100644
> --- a/examples/l3fwd/l3fwd.h
> +++ b/examples/l3fwd/l3fwd.h
> @@ -35,7 +35,7 @@
>  /*
>   * Try to avoid TX buffering if we have at least MAX_TX_BURST packets to send.
>   */
> -#define	MAX_TX_BURST	  (MAX_PKT_BURST / 2)
> +#define	MAX_TX_BURST	  (DEFAULT_PKT_BURST / 2)
> 
>  #define NB_SOCKETS        8
> 
> @@ -152,8 +152,8 @@ send_single_packet(struct lcore_conf *qconf,
>  	len++;
> 
>  	/* enough pkts to be sent */
> -	if (unlikely(len == MAX_PKT_BURST)) {
> -		send_burst(qconf, MAX_PKT_BURST, port);
> +	if (unlikely(len == nb_pkt_per_burst)) {
> +		send_burst(qconf, nb_pkt_per_burst, port);
>  		len = 0;
>  	}
> 
> diff --git a/examples/l3fwd/l3fwd_common.h b/examples/l3fwd/l3fwd_common.h
> index d94e5f1357..6cb7de5144 100644
> --- a/examples/l3fwd/l3fwd_common.h
> +++ b/examples/l3fwd/l3fwd_common.h
> @@ -25,6 +25,9 @@
>   */
>  #define SENDM_PORT_OVERHEAD(x) (x)
> 
> +extern uint32_t nb_pkt_per_burst;
> +extern uint32_t max_tx_burst;
> +
>  /*
>   * From http://www.rfc-editor.org/rfc/rfc1812.txt section 5.2.2:
>   * - The IP version number must be 4.
> @@ -71,7 +74,7 @@ send_packetsx4(struct lcore_conf *qconf, uint16_t port, struct rte_mbuf *m[],
>  	 * If TX buffer for that queue is empty, and we have enough packets,
>  	 * then send them straightway.
>  	 */
> -	if (num >= MAX_TX_BURST && len == 0) {
> +	if (num >= max_tx_burst && len == 0) {
>  		n = rte_eth_tx_burst(port, qconf->tx_queue_id[port], m, num);
>  		if (unlikely(n < num)) {
>  			do {
> @@ -86,7 +89,7 @@ send_packetsx4(struct lcore_conf *qconf, uint16_t port, struct rte_mbuf *m[],
>  	 */
> 
>  	n = len + num;
> -	n = (n > MAX_PKT_BURST) ? MAX_PKT_BURST - len : num;
> +	n = (n > nb_pkt_per_burst) ? nb_pkt_per_burst - len : num;
> 
>  	j = 0;
>  	switch (n % FWDSTEP) {
> @@ -112,9 +115,9 @@ send_packetsx4(struct lcore_conf *qconf, uint16_t port, struct rte_mbuf *m[],
>  	len += n;
> 
>  	/* enough pkts to be sent */
> -	if (unlikely(len == MAX_PKT_BURST)) {
> +	if (unlikely(len == nb_pkt_per_burst)) {
> 
> -		send_burst(qconf, MAX_PKT_BURST, port);
> +		send_burst(qconf, nb_pkt_per_burst, port);
> 
>  		/* copy rest of the packets into the TX buffer. */
>  		len = num - n;
> diff --git a/examples/l3fwd/main.c b/examples/l3fwd/main.c
> index 994b7dd8e5..4cabd05be2 100644
> --- a/examples/l3fwd/main.c
> +++ b/examples/l3fwd/main.c
> @@ -59,6 +59,7 @@ uint16_t nb_rxd = RX_DESC_DEFAULT;
>  uint16_t nb_txd = TX_DESC_DEFAULT;
>  uint32_t nb_pkt_per_burst = DEFAULT_PKT_BURST;
>  uint32_t mb_mempool_cache_size = MEMPOOL_CACHE_SIZE;
> +uint32_t max_tx_burst = MAX_TX_BURST;
> 
>  /**< Ports set in promiscuous mode off by default. */
>  static int promiscuous_on;
> @@ -733,6 +734,7 @@ parse_pkt_burst(const char *optarg)
>  		return;
>  	}
>  	nb_pkt_per_burst = burst_size;
> +	max_tx_burst = burst_size / 2;

Might be a bit better then to completely remove MAX_TX_BURST,
and just always set:
max_tx_burst = nb_pkt_per_burst / 2;

>  	RTE_LOG(INFO, L3FWD, "Using PMD-provided burst value %d\n", burst_size);
>  }
> 
> --
> 2.34.1