diff options
| author | Eric W. Biederman <ebiederm@xmission.com> | 2011-10-13 22:25:23 +0000 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2011-10-19 16:59:42 -0400 |
| commit | 850a545bd8a41648445bfc5541afe36ca105b0b8 (patch) | |
| tree | c3d3da6af635780cc67bcd95951aa21d7b435442 | |
| parent | 06a59ecb921de1d44efcf2cdf543bc689fe2e0d8 (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>
| -rw-r--r-- | net/core/dev.c | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/net/core/dev.c b/net/core/dev.c index cbb5918e4fc..09aef266d4d 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); |