netdev - [PATCH net-next 4/4] net: no longer stop all TX queues in dev

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Message-Id: <20211117032924.1740327-5-eric.dumazet@gmail.com>
Date:   Tue, 16 Nov 2021 19:29:24 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH net-next 4/4] net: no longer stop all TX queues in dev_watchdog()

From: Eric Dumazet <edumazet@...gle.com>

There is no reason for stopping all TX queues from dev_watchdog()

Not only this stops feeding the NIC, it also migrates all qdiscs
to be serviced on the cpu calling netif_tx_unlock(), causing
a potential latency artifact.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/sched/sch_generic.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 389e0d8fc68d12cf092a975511729a8dae1b29fb..d33804d41c5c5a9047c808fd37ba65ae8875fc79 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -500,7 +500,7 @@ static void dev_watchdog(struct timer_list *t)
 {
 	struct net_device *dev = from_timer(dev, t, watchdog_timer);
 
-	netif_tx_lock(dev);
+	spin_lock(&dev->tx_global_lock);
 	if (!qdisc_tx_is_noop(dev)) {
 		if (netif_device_present(dev) &&
 		    netif_running(dev) &&
@@ -523,11 +523,13 @@ static void dev_watchdog(struct timer_list *t)
 				}
 			}
 
-			if (some_queue_timedout) {
+			if (unlikely(some_queue_timedout)) {
 				trace_net_dev_xmit_timeout(dev, i);
 				WARN_ONCE(1, KERN_INFO "NETDEV WATCHDOG: %s (%s): transmit queue %u timed out\n",
 				       dev->name, netdev_drivername(dev), i);
+				netif_freeze_queues(dev);
 				dev->netdev_ops->ndo_tx_timeout(dev, i);
+				netif_unfreeze_queues(dev);
 			}
 			if (!mod_timer(&dev->watchdog_timer,
 				       round_jiffies(jiffies +
@@ -535,7 +537,7 @@ static void dev_watchdog(struct timer_list *t)
 				dev_hold(dev);
 		}
 	}
-	netif_tx_unlock(dev);
+	spin_unlock(&dev->tx_global_lock);
 
 	dev_put(dev);
 }
-- 
2.34.0.rc1.387.gb447b232ab-goog