This is a note to let you know that I've just added the patch titled
xen-netfront: transmit fully GSO-sized packets
to the 3.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
xen-netfront-transmit-fully-gso-sized-packets.patch
and it can be found in the queue-3.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.
>From foo@baz Tue Apr 21 23:05:14 CEST 2015
From: Jonathan Davies <jonathan.dav...@citrix.com>
Date: Tue, 31 Mar 2015 11:05:15 +0100
Subject: xen-netfront: transmit fully GSO-sized packets
From: Jonathan Davies <jonathan.dav...@citrix.com>
[ Upstream commit 0c36820e2ab7d943ab1188230fdf2149826d33c0 ]
xen-netfront limits transmitted skbs to be at most 44 segments in size. However,
GSO permits up to 65536 bytes, which means a maximum of 45 segments of 1448
bytes each. This slight reduction in the size of packets means a slight loss in
efficiency.
Since c/s 9ecd1a75d, xen-netfront sets gso_max_size to
XEN_NETIF_MAX_TX_SIZE - MAX_TCP_HEADER,
where XEN_NETIF_MAX_TX_SIZE is 65535 bytes.
The calculation used by tcp_tso_autosize (and also tcp_xmit_size_goal since c/s
6c09fa09d) in determining when to split an skb into two is
sk->sk_gso_max_size - 1 - MAX_TCP_HEADER.
So the maximum permitted size of an skb is calculated to be
(XEN_NETIF_MAX_TX_SIZE - MAX_TCP_HEADER) - 1 - MAX_TCP_HEADER.
Intuitively, this looks like the wrong formula -- we don't need two TCP headers.
Instead, there is no need to deviate from the default gso_max_size of 65536 as
this already accommodates the size of the header.
Currently, the largest skb transmitted by netfront is 63712 bytes (44 segments
of 1448 bytes each), as observed via tcpdump. This patch makes netfront send
skbs of up to 65160 bytes (45 segments of 1448 bytes each).
Similarly, the maximum allowable mtu does not need to subtract MAX_TCP_HEADER as
it relates to the size of the whole packet, including the header.
Fixes: 9ecd1a75d977 ("xen-netfront: reduce gso_max_size to account for max TCP
header")
Signed-off-by: Jonathan Davies <jonathan.dav...@citrix.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
drivers/net/xen-netfront.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -1062,8 +1062,7 @@ err:
static int xennet_change_mtu(struct net_device *dev, int mtu)
{
- int max = xennet_can_sg(dev) ?
- XEN_NETIF_MAX_TX_SIZE - MAX_TCP_HEADER : ETH_DATA_LEN;
+ int max = xennet_can_sg(dev) ? XEN_NETIF_MAX_TX_SIZE : ETH_DATA_LEN;
if (mtu > max)
return -EINVAL;
@@ -1333,8 +1332,6 @@ static struct net_device *xennet_create_
netdev->ethtool_ops = &xennet_ethtool_ops;
SET_NETDEV_DEV(netdev, &dev->dev);
- netif_set_gso_max_size(netdev, XEN_NETIF_MAX_TX_SIZE - MAX_TCP_HEADER);
-
np->netdev = netdev;
netif_carrier_off(netdev);
Patches currently in stable-queue which might be from
jonathan.dav...@citrix.com are
queue-3.19/xen-netfront-transmit-fully-gso-sized-packets.patch
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