Some virtual devices like VLAN's or bridges by default have not transmit queue.
In order to do queuing disciplines on these devices a queue must be added
by setting transmit queue length. The kernel allows doing this at any time, but
setting the queue length value is not enough. Setting the queue length does
not create the transmit queue (going from 0 to non-zero) or destroy it
(setting to zero); the queue is only created (or destroyed) when device
comes up (or goes down).

This patch handles this be doing the necessary activations.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>

---
 include/linux/netdevice.h |    2 ++
 net/core/dev.c            |   19 +++++++++++++++++--
 net/core/net-sysfs.c      |    5 ++---
 net/core/rtnetlink.c      |    2 +-
 4 files changed, 22 insertions(+), 6 deletions(-)

--- a/include/linux/netdevice.h	2009-03-17 11:06:40.358479573 -0700
+++ b/include/linux/netdevice.h	2009-03-17 11:13:55.243604979 -0700
@@ -1436,6 +1436,8 @@ extern int		dev_change_net_namespace(str
 extern int		dev_set_mtu(struct net_device *, int);
 extern int		dev_set_mac_address(struct net_device *,
 					    struct sockaddr *);
+extern int		dev_set_tx_queue_len(struct net_device *dev,
+					     unsigned long len);
 extern int		dev_hard_start_xmit(struct sk_buff *skb,
 					    struct net_device *dev,
 					    struct netdev_queue *txq);
--- a/net/core/dev.c	2009-03-17 11:05:54.919541341 -0700
+++ b/net/core/dev.c	2009-03-17 11:16:25.717479320 -0700
@@ -983,6 +983,22 @@ int dev_set_alias(struct net_device *dev
 	return len;
 }
 
+/**
+ *
+ *	@dev: device
+ *	@len: limit of frames in transmit queue
+ *
+ *	Set ifalias for a device,
+ */
+int dev_set_tx_queue_len(struct net_device *dev, unsigned long len)
+{
+	if (dev->flags & IFF_UP)
+		dev_deactivate(dev);
+	dev->tx_queue_len = len;
+	if (dev->flags & IFF_UP)
+		dev_activate(dev);
+	return 0;
+}
 
 /**
  *	netdev_features_change - device changes features
@@ -3975,8 +3991,7 @@ static int ...
[ message continues ]

That seems quite heavy-weight in case of hierarchical qdiscs, it will
walk and reset the entire tree and looses all state, including packets
as a side effect. Its also a bit inconsistent since it only affects
the default pfifos at the root, not the inner default qdiscs if I'm
not mistaken.

A less intrusive way would be to simply use dev->tx_queue_len directly
in pfifo when no limit is configured. That would require to make a
runtime decision for each packet though. Two more alternatives:

- add a special pfifo variant that always uses tx_queue_len. Duplication
   comes down to pfifo_enqueue (a few lines) and a new struct Qdisc_ops

- if you really only care about the root, reconfigure it explicitly
   using fifo_set_limit()




--

[ message continues ]

On Wed, 18 Mar 2009 18:15:38 +0100

The problem is when setting limit to 0 to force noop and setting it
to non-zero to force pfifo_fast back again.
--

[ message continues ]

I'd suggest to simply attach a pfifo qdisc with an explicitly
configured limit to activate queueing on virtual devices.
--

[ message continues ]

On Wed, 18 Mar 2009 19:08:07 +0100

The existing code is broken if user does:

# ip li set dev eth0.200 txq 200
# tc qdisc set dev eth0.200 root sfq
# tc qdisc del dev eth0.200 root
# ip li set dev eth0.200 txq 0

The vlan is now dead because it is impossible to go back
to the no queueing (noop) qdisc.  Also, when doing performance tests
it is useful to be able to turn off transmit queue entirely.

Other alternative would be to reject changes to txq when device is
up, but that probably would break existing users. And would be a pain
in the ass when trying to configure PPP and tunnel endpoints.

--

[ message continues ]

What I meant is:

# ip l l dummy0
109: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state 
UNKNOWN
     link/ether 0a:94:90:3c:e3:45 brd ff:ff:ff:ff:ff:ff

# tc qdisc add dev dummy0 root pfifo limit 1000
# ip l l dummy0
109: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo state 
UNKNOWN
     link/ether 0a:94:90:3c:e3:45 brd ff:ff:ff:ff:ff:ff

# tc qdisc del dev dummy0 root
# ip l l dummy0
109: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state 
UNKNOWN
     link/ether 0a:94:90:3c:e3:45 brd ff:ff:ff:ff:ff:ff

It should work your way as well if you set the transmit queue length
to zero before removing the root qdisc.
--

[ message continues ]

Some virtual devices like VLAN's or bridges by default have not transmit queue.
In order to do queuing disciplines on these devices a queue must be added
by setting transmit queue length. The kernel allows doing this at any time, but
setting the queue length value is not enough. Setting the queue length does
not create the transmit queue (going from 0 to non-zero) or destroy it
(setting to zero); the queue is only created (or destroyed) when device
comes up (or goes down).

This patch handles this be doing the necessary activations.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>

---
 include/linux/netdevice.h |    2 ++
 net/core/dev.c            |   19 +++++++++++++++++--
 net/core/net-sysfs.c      |    5 ++---
 net/core/rtnetlink.c      |    2 +-
 4 files changed, 22 insertions(+), 6 deletions(-)

--- a/include/linux/netdevice.h	2009-03-17 11:06:40.358479573 -0700
+++ b/include/linux/netdevice.h	2009-03-17 11:13:55.243604979 -0700
@@ -1436,6 +1436,8 @@ extern int		dev_change_net_namespace(str
 extern int		dev_set_mtu(struct net_device *, int);
 extern int		dev_set_mac_address(struct net_device *,
 					    struct sockaddr *);
+extern int		dev_set_tx_queue_len(struct net_device *dev,
+					     unsigned long len);
 extern int		dev_hard_start_xmit(struct sk_buff *skb,
 					    struct net_device *dev,
 					    struct netdev_queue *txq);
--- a/net/core/dev.c	2009-03-17 11:05:54.919541341 -0700
+++ b/net/core/dev.c	2009-03-18 11:11:12.678298789 -0700
@@ -983,6 +983,30 @@ int dev_set_alias(struct net_device *dev
 	return len;
 }
 
+/**
+ *
+ *	@dev: device
+ *	@len: limit of frames in transmit queue
+ *
+ *	Set transmit queue length for device.
+ *	If queue length is set to 0, then queueing is disabled.
+ */
+int dev_set_tx_queue_len(struct net_device *dev, unsigned long len)
+{
+	if (len == dev->tx_queue_len)
+		return 0;
+
+	if ((dev->tx_queue_len != 0) && (len != 0))
+		dev->tx_queue_len = len;
+	else {
+		if (dev->flags & ...
[ message continues ]

if (dev->tx_queue_len == len)




--

[ message continues ]

On Wed, 18 Mar 2009 18:18:44 +0100

Also could do:
         
if ((dev->tx_queue_len != 0) && (len != 0)) {
      dev->tx_queue_len = len;
      return 0;
}
--

[ message continues ]