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authorEric W. Biederman <ebiederm@xmission.com>2011-10-13 22:25:23 +0000
committerDavid S. Miller <davem@davemloft.net>2011-10-19 16:59:42 -0400
commit850a545bd8a41648445bfc5541afe36ca105b0b8 (patch)
treec3d3da6af635780cc67bcd95951aa21d7b435442 /net/core
parent06a59ecb921de1d44efcf2cdf543bc689fe2e0d8 (diff)
net: Move rcu_barrier from rollback_registered_many to netdev_run_todo.
This patch moves the rcu_barrier from rollback_registered_many (inside the rtnl_lock) into netdev_run_todo (just outside the rtnl_lock). This allows us to gain the full benefit of sychronize_net calling synchronize_rcu_expedited when the rtnl_lock is held. The rcu_barrier in rollback_registered_many was originally a synchronize_net but was promoted to be a rcu_barrier() when it was found that people were unnecessarily hitting the 250ms wait in netdev_wait_allrefs(). Changing the rcu_barrier back to a synchronize_net is therefore safe. Since we only care about waiting for the rcu callbacks before we get to netdev_wait_allrefs() it is also safe to move the wait into netdev_run_todo. This was tested by creating and destroying 1000 tap devices and observing /proc/lock_stat. /proc/lock_stat reports this change reduces the hold times of the rtnl_lock by a factor of 10. There was no observable difference in the amount of time it takes to destroy a network device. Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/core')
-rw-r--r--net/core/dev.c8
1 files changed, 7 insertions, 1 deletions
diff --git a/net/core/dev.c b/net/core/dev.c
index cbb5918e4fc5..09aef266d4d1 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5235,7 +5235,7 @@ static void rollback_registered_many(struct list_head *head)
dev = list_first_entry(head, struct net_device, unreg_list);
call_netdevice_notifiers(NETDEV_UNREGISTER_BATCH, dev);
- rcu_barrier();
+ synchronize_net();
list_for_each_entry(dev, head, unreg_list)
dev_put(dev);
@@ -5748,6 +5748,12 @@ void netdev_run_todo(void)
__rtnl_unlock();
+ /* Wait for rcu callbacks to finish before attempting to drain
+ * the device list. This usually avoids a 250ms wait.
+ */
+ if (!list_empty(&list))
+ rcu_barrier();
+
while (!list_empty(&list)) {
struct net_device *dev
= list_first_entry(&list, struct net_device, todo_list);