| Message ID | m1r52g7zf0.fsf@fess.ebiederm.org |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
From: ebiederm@xmission.com (Eric W. Biederman) Date: Fri, 14 Oct 2011 01:25:23 -0700 > > 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> Applied to net-next, thanks Eric. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
difference in the amount of time it takes to destroy a network device. Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> --- 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 70ecb86..44dcacf 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);