From 3137663dfb43bb3e3174e9da81db0c05f395fc1b Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 19 May 2011 23:42:09 +0000 Subject: net: avoid synchronize_rcu() in dev_deactivate_many dev_deactivate_many() issues one synchronize_rcu() call after qdiscs set to noop_qdisc. This call is here to make sure they are no outstanding qdisc-less dev_queue_xmit calls before returning to caller. But in dismantle phase, we dont have to wait, because we wont activate again the device, and we are going to wait one rcu grace period later in rollback_registered_many(). After this patch, device dismantle uses one synchronize_net() and one rcu_barrier() call only, so we have a ~30% speedup and a smaller RTNL latency. Signed-off-by: Eric Dumazet CC: Patrick McHardy , CC: Ben Greear Signed-off-by: David S. Miller --- net/sched/sch_generic.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) (limited to 'net/sched/sch_generic.c') diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index c84b65920d1b..b1721d71c27c 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -815,9 +815,17 @@ static bool some_qdisc_is_busy(struct net_device *dev) return false; } +/** + * dev_deactivate_many - deactivate transmissions on several devices + * @head: list of devices to deactivate + * + * This function returns only when all outstanding transmissions + * have completed, unless all devices are in dismantle phase. + */ void dev_deactivate_many(struct list_head *head) { struct net_device *dev; + bool sync_needed = false; list_for_each_entry(dev, head, unreg_list) { netdev_for_each_tx_queue(dev, dev_deactivate_queue, @@ -827,10 +835,15 @@ void dev_deactivate_many(struct list_head *head) &noop_qdisc); dev_watchdog_down(dev); + sync_needed |= !dev->dismantle; } - /* Wait for outstanding qdisc-less dev_queue_xmit calls. */ - synchronize_rcu(); + /* Wait for outstanding qdisc-less dev_queue_xmit calls. + * This is avoided if all devices are in dismantle phase : + * Caller will call synchronize_net() for us + */ + if (sync_needed) + synchronize_net(); /* Wait for outstanding qdisc_run calls. */ list_for_each_entry(dev, head, unreg_list) -- cgit v1.2.2