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net: Introduce dev_get_by_index_rcu() 

Some workloads hit dev_base_lock rwlock pretty hard.
We can use RCU lookups to avoid touching this rwlock.

netdevices are already freed after a RCU grace period, so this patch
adds no penalty at device dismantle time.

dev_ifname() converted to dev_get_by_index_rcu()

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2009-10-19 19:18:49 +00:00 committed by David S. Miller
parent e0c5567d06
commit fb699dfd42
2 changed files with 39 additions and 10 deletions
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1
include/linux/netdevice.h
View File

@ -1139,6 +1139,7 @@ extern void netdev_resync_ops(struct net_device *dev);
extern int call_netdevice_notifiers(unsigned long val, struct net_device *dev);
extern struct net_device *dev_get_by_index(struct net *net, int ifindex);
extern struct net_device *__dev_get_by_index(struct net *net, int ifindex);
extern struct net_device *dev_get_by_index_rcu(struct net *net, int ifindex);
extern int dev_restart(struct net_device *dev);
#ifdef CONFIG_NETPOLL_TRAP
extern int netpoll_trap(void);

48
net/core/dev.c
View File

@ -214,12 +214,15 @@ static int list_netdevice(struct net_device *dev)
write_lock_bh(&dev_base_lock);
list_add_tail(&dev->dev_list, &net->dev_base_head);
hlist_add_head(&dev->name_hlist, dev_name_hash(net, dev->name));
hlist_add_head(&dev->index_hlist, dev_index_hash(net, dev->ifindex));
hlist_add_head_rcu(&dev->index_hlist,
dev_index_hash(net, dev->ifindex));
write_unlock_bh(&dev_base_lock);
return 0;
}
/* Device list removal */
/* Device list removal
* caller must respect a RCU grace period before freeing/reusing dev
*/
static void unlist_netdevice(struct net_device *dev)
{
ASSERT_RTNL();
@ -228,7 +231,7 @@ static void unlist_netdevice(struct net_device *dev)
write_lock_bh(&dev_base_lock);
list_del(&dev->dev_list);
hlist_del(&dev->name_hlist);
hlist_del(&dev->index_hlist);
hlist_del_rcu(&dev->index_hlist);
write_unlock_bh(&dev_base_lock);
}
@ -646,6 +649,31 @@ struct net_device *__dev_get_by_index(struct net *net, int ifindex)
}
EXPORT_SYMBOL(__dev_get_by_index);
/**
* dev_get_by_index_rcu - find a device by its ifindex
* @net: the applicable net namespace
* @ifindex: index of device
*
* Search for an interface by index. Returns %NULL if the device
* is not found or a pointer to the device. The device has not
* had its reference counter increased so the caller must be careful
* about locking. The caller must hold RCU lock.
*/
struct net_device *dev_get_by_index_rcu(struct net *net, int ifindex)
{
struct hlist_node *p;
struct net_device *dev;
struct hlist_head *head = dev_index_hash(net, ifindex);
hlist_for_each_entry_rcu(dev, p, head, index_hlist)
if (dev->ifindex == ifindex)
return dev;
return NULL;
}
EXPORT_SYMBOL(dev_get_by_index_rcu);
/**
* dev_get_by_index - find a device by its ifindex
@ -662,11 +690,11 @@ struct net_device *dev_get_by_index(struct net *net, int ifindex)
{
struct net_device *dev;
read_lock(&dev_base_lock);
dev = __dev_get_by_index(net, ifindex);
rcu_read_lock();
dev = dev_get_by_index_rcu(net, ifindex);
if (dev)
dev_hold(dev);
read_unlock(&dev_base_lock);
rcu_read_unlock();
return dev;
}
EXPORT_SYMBOL(dev_get_by_index);
@ -2939,15 +2967,15 @@ static int dev_ifname(struct net *net, struct ifreq __user *arg)
if (copy_from_user(&ifr, arg, sizeof(struct ifreq)))
return -EFAULT;
read_lock(&dev_base_lock);
dev = __dev_get_by_index(net, ifr.ifr_ifindex);
rcu_read_lock();
dev = dev_get_by_index_rcu(net, ifr.ifr_ifindex);
if (!dev) {
read_unlock(&dev_base_lock);
rcu_read_unlock();
return -ENODEV;
}
strcpy(ifr.ifr_name, dev->name);
read_unlock(&dev_base_lock);
rcu_read_unlock();
if (copy_to_user(arg, &ifr, sizeof(struct ifreq)))
return -EFAULT;