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>
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index f8c3619..505a3c6 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -447,12 +447,18 @@
};
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;
