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Date: Sun, 08 Mar 2015 22:21:34 -0400 (EDT)
From: David Miller <davem@...emloft.net>
To: noureddine@...sta.com
Cc: kaber@...sh.net, eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] vlan: avoid a synchronize_net when parent
device goes down
From: Salam Noureddine <noureddine@...sta.com>
Date: Thu, 5 Mar 2015 15:37:01 -0800
> When a parent device is brought down, all of the vlan devices
> on top of it are brought down in vlan_device_event which ultimately
> leads to a call to synchronize_net in dev_deactivate_many. If many
> vlan devices are configured on top of one device, these calls can
> take a significant time. This patch works around this issue by
> setting the dismantle flag in vlandev. It is a bit hacky and
> overloads the meaning of dismantle but can bring a big improvement
> on busy systems where synchronize_net can take longer than usual.
>
> The call stack leading to the synchronize_net is,
>
> [<ffffffff812f8747>] synchronize_net+0x25/0x2e
> [<ffffffff8130f94a>] dev_deactivate_many+0x186/0x222
> [<ffffffff812fb7a8>] __dev_close_many+0x83/0xca
> [<ffffffff812fb820>] __dev_close+0x31/0x42
> [<ffffffff812f9220>] __dev_change_flags+0xa8/0x12b
> [<ffffffff812fc42c>] dev_change_flags+0x1c/0x51
> [<ffffffffa00ab6be>] vlan_device_event+0x39a/0x4cc [8021q]
> [<ffffffff813d982b>] notifier_call_chain+0x32/0x5e
> [<ffffffff8104642c>] raw_notifier_call_chain+0xf/0x11
> [<ffffffff812fb720>] call_netdevice_notifiers+0x45/0x4a
> [<ffffffff812fb8e3>] dev_close_many+0xb2/0xfd
>
> Signed-off-by: Salam Noureddine <noureddine@...sta.com>
Please let's implement this properly. VLAN is not the only case
that would benefit from something like this.
Something like:
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 4541378..df0753f 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2185,6 +2185,7 @@ struct net_device *__dev_get_by_name(struct net *net, const char *name);
int dev_alloc_name(struct net_device *dev, const char *name);
int dev_open(struct net_device *dev);
int dev_close(struct net_device *dev);
+int dev_close_many(struct list_head *head, bool unlink);
void dev_disable_lro(struct net_device *dev);
int dev_loopback_xmit(struct sk_buff *newskb);
int dev_queue_xmit(struct sk_buff *skb);
diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
index 64c6bed..98a30a5 100644
--- a/net/8021q/vlan.c
+++ b/net/8021q/vlan.c
@@ -413,7 +413,10 @@ static int vlan_device_event(struct notifier_block *unused, unsigned long event,
vlan_transfer_features(dev, vlandev);
break;
- case NETDEV_DOWN:
+ case NETDEV_DOWN: {
+ struct net_device *tmp;
+ LIST_HEAD(close_list);
+
if (dev->features & NETIF_F_HW_VLAN_CTAG_FILTER)
vlan_vid_del(dev, htons(ETH_P_8021Q), 0);
@@ -425,11 +428,18 @@ static int vlan_device_event(struct notifier_block *unused, unsigned long event,
vlan = vlan_dev_priv(vlandev);
if (!(vlan->flags & VLAN_FLAG_LOOSE_BINDING))
- dev_change_flags(vlandev, flgs & ~IFF_UP);
+ list_add(&vlandev->close_list, &close_list);
+ }
+
+ dev_close_many(&close_list, false);
+
+ list_for_each_entry_safe(vlandev, tmp, &close_list, close_list) {
netif_stacked_transfer_operstate(dev, vlandev);
+ list_del_init(&vlandev->close_list);
}
+ list_del(&close_list);
break;
-
+ }
case NETDEV_UP:
/* Put all VLANs for this dev in the up state too. */
vlan_group_for_each_dev(grp, i, vlandev) {
diff --git a/net/core/dev.c b/net/core/dev.c
index 962ee9d..d190c32 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -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;
@@ -5968,7 +5970,7 @@ 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. */
--
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