[PATCH] net: core: explicitly call linkwatch_fire_event to speed up the startup of network services

[Wen Yang <wenyang@linux.alibaba.com>]

The linkwatch_event work queue runs up to one second later.
When the MicroVM starts, it takes 300+ms for the ethX flag
to change from '+UP +LOWER_UP' to '+RUNNING', as follows:
Jul 20 22:00:47.432552 systemd-networkd[210]: eth0: bringing link up
...
Jul 20 22:00:47.446108 systemd-networkd[210]: eth0: flags change: +UP +LOWER_UP
...
Jul 20 22:00:47.781463 systemd-networkd[210]: eth0: flags change: +RUNNING

Let's manually trigger it here to make the network service start faster.

After applying this patch, the time consumption of
systemd-networkd.service was reduced from 366ms to 50ms.

Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jiri Pirko <jiri@mellanox.com>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Julian Wiedmann <jwi@linux.ibm.com>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 net/core/link_watch.c | 3 +++
 net/core/rtnetlink.c  | 1 +
 2 files changed, 4 insertions(+)

diff --git a/net/core/link_watch.c b/net/core/link_watch.c
index 75431ca..6b9d44b 100644
--- a/net/core/link_watch.c
+++ b/net/core/link_watch.c
@@ -98,6 +98,9 @@ static bool linkwatch_urgent_event(struct net_device *dev)
 	if (netif_is_lag_port(dev) || netif_is_lag_master(dev))
 		return true;
 
+	if ((dev->flags & IFF_UP) && dev->operstate == IF_OPER_DOWN)
+		return true;
+
 	return netif_carrier_ok(dev) &&	qdisc_tx_changing(dev);
 }
 
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 58c484a..fd0b3b6 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -2604,6 +2604,7 @@ static int do_setlink(const struct sk_buff *skb,
 				       extack);
 		if (err < 0)
 			goto errout;
+		linkwatch_fire_event(dev);
 	}
 
 	if (tb[IFLA_MASTER]) {
-- 
1.8.3.1