net: avoid synchronize_rcu() in dev_deactivate_many (3137663d) · Commits · 戴 / test

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 <eric.dumazet@gmail.com> CC: Patrick McHardy <kaber@trash.net>, CC: Ben Greear <greearb@candelatech.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/sched/sch_generic.c

+15 −2

Original line number	Diff line number	Diff line
		@@ -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)

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