From: hawk@kernel•org
To: netdev@vger•kernel.org
Cc: hawk@kernel•org, andrew+netdev@lunn•ch, davem@davemloft•net,
edumazet@google•com, kuba@kernel•org, pabeni@redhat•com,
horms@kernel•org, jhs@mojatatu•com, jiri@resnulli•us,
j.koeppeler@tu-berlin•de, kernel-team@cloudflare•com
Subject: [PATCH net-next 3/5] veth: add tx_timeout watchdog as BQL safety net
Date: Tue, 24 Mar 2026 18:47:02 +0100 [thread overview]
Message-ID: <20260324174719.1224337-5-hawk@kernel.org> (raw)
In-Reply-To: <20260324174719.1224337-1-hawk@kernel.org>
From: Jesper Dangaard Brouer <hawk@kernel•org>
With the introduction of BQL (Byte Queue Limits) for veth, there are
now two independent mechanisms that can stop a transmit queue:
- DRV_XOFF: set by netif_tx_stop_queue() when the ptr_ring is full
- STACK_XOFF: set by BQL when the byte-in-flight limit is reached
If either mechanism stalls without a corresponding wake/completion,
the queue stops permanently. Enable the net device watchdog timer and
implement ndo_tx_timeout as a failsafe recovery.
The timeout handler resets BQL state (clearing STACK_XOFF) and wakes
the queue (clearing DRV_XOFF), covering both stop mechanisms. The
watchdog fires after 16 seconds, which accommodates worst-case NAPI
processing (budget=64 packets x 250ms per-packet consumer delay)
without false positives under normal backpressure.
Signed-off-by: Jesper Dangaard Brouer <hawk@kernel•org>
Tested-by: Jonas Köppeler <j.koeppeler@tu-berlin•de>
---
drivers/net/veth.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index b9a79d066703..beb4c31d8fd7 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -1426,6 +1426,22 @@ static int veth_set_channels(struct net_device *dev,
goto out;
}
+static void veth_tx_timeout(struct net_device *dev, unsigned int txqueue)
+{
+ struct netdev_queue *txq = netdev_get_tx_queue(dev, txqueue);
+
+ netdev_err(dev,
+ "veth backpressure(0x%lX) stalled(n:%ld) TXQ(%u) re-enable\n",
+ txq->state, atomic_long_read(&txq->trans_timeout), txqueue);
+
+ /* Clear both stop mechanisms:
+ * - DRV_XOFF: set by netif_tx_stop_queue (ptr_ring backpressure)
+ * - STACK_XOFF: set by BQL when byte limit is reached
+ */
+ netdev_tx_reset_queue(txq);
+ netif_tx_wake_queue(txq);
+}
+
static int veth_open(struct net_device *dev)
{
struct veth_priv *priv = netdev_priv(dev);
@@ -1764,6 +1780,7 @@ static const struct net_device_ops veth_netdev_ops = {
.ndo_bpf = veth_xdp,
.ndo_xdp_xmit = veth_ndo_xdp_xmit,
.ndo_get_peer_dev = veth_peer_dev,
+ .ndo_tx_timeout = veth_tx_timeout,
};
static const struct xdp_metadata_ops veth_xdp_metadata_ops = {
@@ -1803,6 +1820,7 @@ static void veth_setup(struct net_device *dev)
dev->priv_destructor = veth_dev_free;
dev->pcpu_stat_type = NETDEV_PCPU_STAT_TSTATS;
dev->max_mtu = ETH_MAX_MTU;
+ dev->watchdog_timeo = msecs_to_jiffies(16000);
dev->hw_features = VETH_FEATURES;
dev->hw_enc_features = VETH_FEATURES;
--
2.43.0
next prev parent reply other threads:[~2026-03-24 17:48 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-24 17:46 [PATCH net-next 0/5] veth: add Byte Queue Limits (BQL) support hawk
2026-03-24 17:46 ` [PATCH " hawk
2026-03-24 17:56 ` Jesper Dangaard Brouer
2026-03-24 17:47 ` [PATCH net-next 1/5] net: add dev->bql flag to allow BQL sysfs for IFF_NO_QUEUE devices hawk
2026-03-24 17:47 ` [PATCH net-next 2/5] veth: implement Byte Queue Limits (BQL) for latency reduction hawk
2026-03-24 17:47 ` hawk [this message]
2026-03-24 17:47 ` [PATCH net-next 4/5] net: sched: add timeout count to NETDEV WATCHDOG message hawk
2026-03-24 17:47 ` [PATCH net-next 5/5] selftests: net: add veth BQL stress test hawk
2026-03-26 12:19 ` Jesper Dangaard Brouer
2026-03-26 19:55 ` Jakub Kicinski
2026-03-28 15:19 ` Simon Schippers
[not found] ` <1c435d90-8d08-4ac1-8b84-cc72c0b4e30f@tu-berlin.de>
2026-04-30 9:45 ` Simon Schippers
2026-04-30 12:31 ` Jesper Dangaard Brouer
[not found] ` <a841e7ed-eee0-4069-bd0d-ab043a1509c5@tu-berlin.de>
2026-05-01 20:35 ` Simon Schippers
2026-03-27 9:50 ` [PATCH net-next 0/5] veth: add Byte Queue Limits (BQL) support Toke Høiland-Jørgensen
2026-03-27 12:49 ` Jesper Dangaard Brouer
2026-03-27 15:37 ` Jonas Köppeler
2026-03-28 20:06 ` Toke Høiland-Jørgensen
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