[PATCH] examples/l3fwd: fix Tx performance deteriorate

[PATCH] examples/l3fwd: fix Tx performance deteriorate

[Jie Hai]

The application send packets only when the buffer is full, or the
buffer is empty and the number of packets to be sent extends half
of the buffer.

The change of MAX_PKT_BURST increases TX buffer size, while the
default size of local cache on each lcore is 256, which not greater
than the limit of transmitting. That would make the mbuf not on the
local cache be frequently used and the performance deteriorates.

This problem can be solved by making the TX threshold smaller than
the local cache size. For example, use the '--mbcache' parameter to
make the local cache greater. This patch optimizes the default
performance by lowering TX threshold.

Fixes: d5c4897ecfb2 ("examples/l3fwd: add option to set Rx burst size")

Signed-off-by: Jie Hai <haijie1@huawei.com>
---
 examples/l3fwd/l3fwd.h        | 8 +++++---
 examples/l3fwd/l3fwd_common.h | 6 +++---
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/examples/l3fwd/l3fwd.h b/examples/l3fwd/l3fwd.h
index 0cce3406ee7d..a01fecd51261 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
 
 #define NB_SOCKETS        8
 
@@ -57,6 +57,8 @@
 #define L3FWD_HASH_ENTRIES		(1024*1024*1)
 #endif
 
+static_assert(MAX_TX_BURST <= MAX_PKT_BURST, "MAX_TX_BURST should be at most MAX_PKT_BURST");
+
 struct parm_cfg {
 	const char *rule_ipv4_name;
 	const char *rule_ipv6_name;
@@ -152,8 +154,8 @@ 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 == MAX_TX_BURST)) {
+		send_burst(qconf, MAX_TX_BURST, port);
 		len = 0;
 	}
 
diff --git a/examples/l3fwd/l3fwd_common.h b/examples/l3fwd/l3fwd_common.h
index d94e5f135791..3f504dc0a552 100644
--- a/examples/l3fwd/l3fwd_common.h
+++ b/examples/l3fwd/l3fwd_common.h
@@ -71,7 +71,7 @@ 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 / 2 && len == 0) {
 		n = rte_eth_tx_burst(port, qconf->tx_queue_id[port], m, num);
 		if (unlikely(n < num)) {
 			do {
@@ -112,9 +112,9 @@ 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 > MAX_TX_BURST)) {
 
-		send_burst(qconf, MAX_PKT_BURST, port);
+		send_burst(qconf, len, port);
 
 		/* copy rest of the packets into the TX buffer. */
 		len = num - n;
-- 
2.22.0

Re: [PATCH] examples/l3fwd: fix Tx performance deteriorate

[lihuisong (C)]

LGTM, good job.
Acked-by: Huisong Li <lihuisong@huawei.com>

在 2024/11/22 15:13, Jie Hai 写道:
> The application send packets only when the buffer is full, or the
> buffer is empty and the number of packets to be sent extends half
> of the buffer.
>
> The change of MAX_PKT_BURST increases TX buffer size, while the
> default size of local cache on each lcore is 256, which not greater
> than the limit of transmitting. That would make the mbuf not on the
> local cache be frequently used and the performance deteriorates.
>
> This problem can be solved by making the TX threshold smaller than
> the local cache size. For example, use the '--mbcache' parameter to
> make the local cache greater. This patch optimizes the default
> performance by lowering TX threshold.
>
> Fixes: d5c4897ecfb2 ("examples/l3fwd: add option to set Rx burst size")
>
> Signed-off-by: Jie Hai <haijie1@huawei.com>
> ---
>   examples/l3fwd/l3fwd.h        | 8 +++++---
>   examples/l3fwd/l3fwd_common.h | 6 +++---
>   2 files changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/examples/l3fwd/l3fwd.h b/examples/l3fwd/l3fwd.h
> index 0cce3406ee7d..a01fecd51261 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
>   
>   #define NB_SOCKETS        8
>   
> @@ -57,6 +57,8 @@
>   #define L3FWD_HASH_ENTRIES		(1024*1024*1)
>   #endif
>   
> +static_assert(MAX_TX_BURST <= MAX_PKT_BURST, "MAX_TX_BURST should be at most MAX_PKT_BURST");
> +
>   struct parm_cfg {
>   	const char *rule_ipv4_name;
>   	const char *rule_ipv6_name;
> @@ -152,8 +154,8 @@ 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 == MAX_TX_BURST)) {
> +		send_burst(qconf, MAX_TX_BURST, port);
>   		len = 0;
>   	}
>   
> diff --git a/examples/l3fwd/l3fwd_common.h b/examples/l3fwd/l3fwd_common.h
> index d94e5f135791..3f504dc0a552 100644
> --- a/examples/l3fwd/l3fwd_common.h
> +++ b/examples/l3fwd/l3fwd_common.h
> @@ -71,7 +71,7 @@ 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 / 2 && len == 0) {
>   		n = rte_eth_tx_burst(port, qconf->tx_queue_id[port], m, num);
>   		if (unlikely(n < num)) {
>   			do {
> @@ -112,9 +112,9 @@ 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 > MAX_TX_BURST)) {
>   
> -		send_burst(qconf, MAX_PKT_BURST, port);
> +		send_burst(qconf, len, port);
>   
>   		/* copy rest of the packets into the TX buffer. */
>   		len = num - n;

RE: [PATCH] examples/l3fwd: fix Tx performance deteriorate

[Konstantin Ananyev]

> The application send packets only when the buffer is full, or the
> buffer is empty and the number of packets to be sent extends half
> of the buffer.
> 
> The change of MAX_PKT_BURST increases TX buffer size, while the
> default size of local cache on each lcore is 256, which not greater
> than the limit of transmitting. That would make the mbuf not on the
> local cache be frequently used and the performance deteriorates.
> 
> This problem can be solved by making the TX threshold smaller than
> the local cache size. For example, use the '--mbcache' parameter to
> make the local cache greater. This patch optimizes the default
> performance by lowering TX threshold.

In  commit:
examples/l3fwd: add option to set Rx burst size
you introduced new global 
uint32_t nb_pkt_per_burst;
Why not to use it for both (rx and tx) paths?
Or if necessary introduce another one for tx, so we'll have:
uint32_t nb_rx_pkt_per_burst, nb_tx_pkt_per_burst,;
To me that is much better then create some hardcoded
and implicit thresholds.  

> Fixes: d5c4897ecfb2 ("examples/l3fwd: add option to set Rx burst size")
> 
> Signed-off-by: Jie Hai <haijie1@huawei.com>
> ---
>  examples/l3fwd/l3fwd.h        | 8 +++++---
>  examples/l3fwd/l3fwd_common.h | 6 +++---
>  2 files changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/examples/l3fwd/l3fwd.h b/examples/l3fwd/l3fwd.h
> index 0cce3406ee7d..a01fecd51261 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
> 
>  #define NB_SOCKETS        8
> 
> @@ -57,6 +57,8 @@
>  #define L3FWD_HASH_ENTRIES		(1024*1024*1)
>  #endif
> 
> +static_assert(MAX_TX_BURST <= MAX_PKT_BURST, "MAX_TX_BURST should be at most MAX_PKT_BURST");
> +
>  struct parm_cfg {
>  	const char *rule_ipv4_name;
>  	const char *rule_ipv6_name;
> @@ -152,8 +154,8 @@ 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 == MAX_TX_BURST)) {
> +		send_burst(qconf, MAX_TX_BURST, port);
>  		len = 0;
>  	}
> 
> diff --git a/examples/l3fwd/l3fwd_common.h b/examples/l3fwd/l3fwd_common.h
> index d94e5f135791..3f504dc0a552 100644
> --- a/examples/l3fwd/l3fwd_common.h
> +++ b/examples/l3fwd/l3fwd_common.h
> @@ -71,7 +71,7 @@ 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 / 2 && len == 0) {
>  		n = rte_eth_tx_burst(port, qconf->tx_queue_id[port], m, num);
>  		if (unlikely(n < num)) {
>  			do {
> @@ -112,9 +112,9 @@ 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 > MAX_TX_BURST)) {
> 
> -		send_burst(qconf, MAX_PKT_BURST, port);
> +		send_burst(qconf, len, port);
> 
>  		/* copy rest of the packets into the TX buffer. */
>  		len = num - n;
> --
> 2.22.0