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/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 6242108..f0c2824 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -953,17 +953,12 @@
}
}
+ if (!skb->xmit_more)
+ virtqueue_kick(sq->vq);
+
return NETDEV_TX_OK;
}
-static void xmit_flush(struct net_device *dev, u16 qnum)
-{
- struct virtnet_info *vi = netdev_priv(dev);
- struct send_queue *sq = &vi->sq[qnum];
-
- virtqueue_kick(sq->vq);
-}
-
/*
* Send command via the control virtqueue and check status. Commands
* supported by the hypervisor, as indicated by feature bits, should
@@ -1393,7 +1388,6 @@
.ndo_open = virtnet_open,
.ndo_stop = virtnet_close,
.ndo_start_xmit = start_xmit,
- .ndo_xmit_flush = xmit_flush,
.ndo_validate_addr = eth_validate_addr,
.ndo_set_mac_address = virtnet_set_mac_address,
.ndo_set_rx_mode = virtnet_set_rx_mode,