Re: Slow speed of tcp connections in a network namespace

[Eric Dumazet <eric.dumazet@gmail.com>]

On Sat, 2012-12-29 at 13:24 +0400, Andrew Vagin wrote:
> We found a few nodes, where network works slow in containers.
> 
> For testing speed of TCP connections we use wget, which downloads iso
> images from the internet.
> 
> wget in the new netns reports only 1.5 MB/s, but wget in the root netns
> reports 33MB/s.
> 
> A few facts:
>  * Experiments shows that window size for CT traffic does not increases
>    up to ~900, however for host traffic window size increases up to ~14000
>  * packets are shuffled in the netns sometimes.
>  * tso/gro/gso changes on interfaces does not help
>  * issue was _NOT_ reproduced if kernel booted with maxcpus=1 or bnx2.disable_msi=1
> 
> I reduced steps to reproduce:
> * Create a new network namespace "test" and a veth pair.
>   # ip netns add test
>   # ip link add name veth0 type veth peer name veth1
> 
> * Move veth1 into the netns test
>   # ip link set veth1 netns test
> 
> * Set ip address on veth1 and proper routing rules are added for this ip
>   in the root netns.
>   # ip link set up dev veth0;  ip link set up dev veth0
>   # ip netns exec test ip a add REMOTE dev veth1
>   # ip netns exec test ip r a default via veth1
>   # ip r a REMOTE/32 via dev veth0
> 
> Tcpdump for both cases are attached to this message.
> tcpdump.host - wget in the root netns
> tcpdump.netns.host - tcpdump for the host device, wget in the new netns
> tcpdump.netns.veth - tcpdump for the veth1 device, wget in the new netns
> 
> 3.8-rc1 is used for experiments.
> 
> Do you have any ideas where is a problem?

veth has absolutely no offload features

It needs some care...

At the very miminum, let TCP coalesce do its job by allowing SG

CC Michał Mirosław <mirq-linux@rere.qmqm.pl> for insights.

Please try following patch :

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 95814d9..9fefeb3 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -259,6 +259,10 @@ static const struct net_device_ops veth_netdev_ops = {
 	.ndo_set_mac_address = eth_mac_addr,
 };
 
+#define VETH_FEATURES (NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_TSO |	\
+		       NETIF_F_HW_CSUM | NETIF_F_HIGHDMA |		\
+		       NETIF_F_HW_VLAN_TX | NETIF_F_HW_VLAN_RX)
+
 static void veth_setup(struct net_device *dev)
 {
 	ether_setup(dev);
@@ -269,9 +273,10 @@ static void veth_setup(struct net_device *dev)
 	dev->netdev_ops = &veth_netdev_ops;
 	dev->ethtool_ops = &veth_ethtool_ops;
 	dev->features |= NETIF_F_LLTX;
+	dev->features |= VETH_FEATURES;
 	dev->destructor = veth_dev_free;
 
-	dev->hw_features = NETIF_F_HW_CSUM | NETIF_F_SG | NETIF_F_RXCSUM;
+	dev->hw_features = VETH_FEATURES;
 }
 
 /*