net: Remove ndo_xmit_flush netdev operation, use signalling instead.
As reported by Jesper Dangaard Brouer, for high packet rates the
overhead of having another indirect call in the TX path is
non-trivial.
There is the indirect call itself, and then there is all of the
reloading of the state to refetch the tail pointer value and
then write the device register.
Move to a more passive scheme, which requires very light modifications
to the device drivers.
The signal is a new skb->xmit_more value, if it is non-zero it means
that more SKBs are pending to be transmitted on the same queue as the
current SKB. And therefore, the driver may elide the tail pointer
update.
Right now skb->xmit_more is always zero.
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 18ddf96..9b3802a 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -452,6 +452,7 @@
* @tc_verd: traffic control verdict
* @hash: the packet hash
* @queue_mapping: Queue mapping for multiqueue devices
+ * @xmit_more: More SKBs are pending for this queue
* @ndisc_nodetype: router type (from link layer)
* @ooo_okay: allow the mapping of a socket to a queue to be changed
* @l4_hash: indicate hash is a canonical 4-tuple hash over transport
@@ -558,6 +559,7 @@
__u16 queue_mapping;
kmemcheck_bitfield_begin(flags2);
+ __u8 xmit_more:1;
#ifdef CONFIG_IPV6_NDISC_NODETYPE
__u8 ndisc_nodetype:2;
#endif