Commit 6a321cb3 authored Apr 28, 2009 by Eric Dumazet Committed by David S. Miller Apr 28, 2009

net: netif_tx_queue_stopped too expensive



netif_tx_queue_stopped(txq) is most of the time false.

Yet its cost is very expensive on SMP.

static inline int netif_tx_queue_stopped(const struct netdev_queue *dev_queue)
{
	return test_bit(__QUEUE_STATE_XOFF, &dev_queue->state);
}

I saw this on oprofile hunting and bnx2 driver bnx2_tx_int().

We probably should split "struct netdev_queue" in two parts, one
being read mostly.

__netif_tx_lock() touches _xmit_lock & xmit_lock_owner, these
deserve a separate cache line.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 8555a594

include/linux/netdevice.h

+8 −2

Original line number	Diff line number	Diff line
		@@ -447,12 +447,18 @@ enum netdev_queue_state_t
		};

		struct netdev_queue {
		/*
		* read mostly part
		*/
		struct net_device *dev;
		struct Qdisc *qdisc;
		unsigned long state;
		spinlock_t _xmit_lock;
		int xmit_lock_owner;
		struct Qdisc *qdisc_sleeping;
		/*
		* write mostly part
		*/
		spinlock_t _xmit_lock ____cacheline_aligned_in_smp;
		int xmit_lock_owner;
		} ____cacheline_aligned_in_smp;