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net: Fix high overhead of vlan sub-device teardown.

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When a networking device is taken down that has a non-trivial number
of VLAN devices configured under it, we eat a full synchronize_net()
for every such VLAN device.

This is because of the call chain:

	NETDEV_DOWN notifier
	--> vlan_device_event()
		--> dev_change_flags()
		--> __dev_change_flags()
		--> __dev_close()
		--> __dev_close_many()
		--> dev_deactivate_many()
			--> synchronize_net()

This is kind of rediculous because we already have infrastructure for
batching doing operation X to a list of net devices so that we only
incur one sync.

So make use of that by exporting dev_close_many() and adjusting it's
interfaace so that the caller can fully manage the batch list.  Use
this in vlan_device_event() and all the overhead goes away.

Reported-by: Salam Noureddine <noureddine@arista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David S. Miller
2015-03-18 22:52:33 -04:00
parent 738e6d30d3
commit 99c4a26a15
3 changed files with 21 additions and 8 deletions
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10
net/core/dev.c
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@@ -1385,7 +1385,7 @@ static int __dev_close(struct net_device *dev)
return retval;
}
static int dev_close_many(struct list_head *head)
int dev_close_many(struct list_head *head, bool unlink)
{
struct net_device *dev, *tmp;
@@ -1399,11 +1399,13 @@ static int dev_close_many(struct list_head *head)
list_for_each_entry_safe(dev, tmp, head, close_list) {
rtmsg_ifinfo(RTM_NEWLINK, dev, IFF_UP|IFF_RUNNING, GFP_KERNEL);
call_netdevice_notifiers(NETDEV_DOWN, dev);
list_del_init(&dev->close_list);
if (unlink)
list_del_init(&dev->close_list);
}
return 0;
}
EXPORT_SYMBOL(dev_close_many);
/**
* dev_close - shutdown an interface.
@@ -1420,7 +1422,7 @@ int dev_close(struct net_device *dev)
LIST_HEAD(single);
list_add(&dev->close_list, &single);
dev_close_many(&single);
dev_close_many(&single, true);
list_del(&single);
}
return 0;
@@ -5986,7 +5988,7 @@ static void rollback_registered_many(struct list_head *head)
/* If device is running, close it first. */
list_for_each_entry(dev, head, unreg_list)
list_add_tail(&dev->close_list, &close_head);
dev_close_many(&close_head);
dev_close_many(&close_head, true);
list_for_each_entry(dev, head, unreg_list) {
/* And unlink it from device chain. */