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net: netif_tx_queue_stopped too expensive

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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>
This commit is contained in:
Eric Dumazet 2009-04-28 04:43:42 -07:00 • committed by David S. Miller
commit 6a321cb370
1 changed files with 8 additions and 2 deletions
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10
include/linux/netdevice.h
View file

@ -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;