linux-kernel - [PATCH] bonding: don't force LACPDU tx to ~333 ms boundaries

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Message-Id: <20250625-fix-lacpdu-jitter-v1-1-4d0ee627e1ba@kernel.org>
Date: Wed, 25 Jun 2025 11:01:24 -0500
From: "Seth Forshee (DigitalOcean)" <sforshee@...nel.org>
To: Jay Vosburgh <jv@...sburgh.net>, Andrew Lunn <andrew+netdev@...n.ch>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Carlos Bilbao <carlos.bilbao@...nel.org>, 
 Tonghao Zhang <tonghao@...aicloud.com>, 
 "Seth Forshee (DigitalOcean)" <sforshee@...nel.org>
Subject: [PATCH] bonding: don't force LACPDU tx to ~333 ms boundaries

The timer which ensures that no more than 3 LACPDUs are transmitted in
a second rearms itself every 333ms regardless of whether an LACPDU is
transmitted when the timer expires. This causes LACPDU tx to be delayed
until the next expiration of the timer, which effectively aligns LACPDUs
to ~333ms boundaries. This results in a variable amount of jitter in the
timing of periodic LACPDUs.

Change this to only rearm the timer when an LACPDU is actually sent,
allowing tx at any point after the timer has expired.

Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@...nel.org>
---
 drivers/net/bonding/bond_3ad.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c
index c6807e473ab706afed9560bcdb5e6eca1934f5b7..a8d8aaa169fc09d7d5c201ff298b37b3f11a7ded 100644
--- a/drivers/net/bonding/bond_3ad.c
+++ b/drivers/net/bonding/bond_3ad.c
@@ -1378,7 +1378,7 @@ static void ad_tx_machine(struct port *port)
 	/* check if tx timer expired, to verify that we do not send more than
 	 * 3 packets per second
 	 */
-	if (port->sm_tx_timer_counter && !(--port->sm_tx_timer_counter)) {
+	if (!port->sm_tx_timer_counter || !(--port->sm_tx_timer_counter)) {
 		/* check if there is something to send */
 		if (port->ntt && (port->sm_vars & AD_PORT_LACP_ENABLED)) {
 			__update_lacpdu_from_port(port);
@@ -1393,12 +1393,13 @@ static void ad_tx_machine(struct port *port)
 				 * again until demanded
 				 */
 				port->ntt = false;
+
+				/* restart tx timer(to verify that we will not
+				 * exceed AD_MAX_TX_IN_SECOND
+				 */
+				port->sm_tx_timer_counter = ad_ticks_per_sec / AD_MAX_TX_IN_SECOND;
 			}
 		}
-		/* restart tx timer(to verify that we will not exceed
-		 * AD_MAX_TX_IN_SECOND
-		 */
-		port->sm_tx_timer_counter = ad_ticks_per_sec/AD_MAX_TX_IN_SECOND;
 	}
 }

---
base-commit: 86731a2a651e58953fc949573895f2fa6d456841
change-id: 20250625-fix-lacpdu-jitter-1554d9f600ab

Best regards,
-- 
Seth Forshee (DigitalOcean) <sforshee@...nel.org>