Re: [PATCH net-next ] Fix time-lag of IFF_RUNNING flag consistency between vlan and real devices

Le dimanche 28 août 2011 à 23:06 -0700, Stephen Hemminger a écrit :

----- Original Message -----

quoted

Le dimanche 28 août 2011 à 22:20 +0900, HAYASAKA Mitsuo a écrit :

quoted

Hi Stephen and Herbert

Thank you for your comments.

(2011/08/26 15:08), Stephen Hemminger wrote:

quoted

I don't think this is the right way to solve the problem.

The flags are supposed to propagate back from real device to vlan
via network notifications.

Just doing this for ioctl is not enough, API's other than user
space depend on this.
Also the user may have manually set different flags on vlan than
on
the real device.

I agreed.
I will try another way to solve this problem, as you said.


(2011/08/26 15:45), Herbert Xu wrote:

quoted

On Thu, Aug 25, 2011 at 11:08:59PM -0700, Stephen Hemminger
wrote:

quoted

Just doing this for ioctl is not enough, API's other than user
space depend on this.
Also the user may have manually set different flags on vlan than
on
the real device.

Right, anything that tests netif_carrier_ok directly on the VLAN
device will still be delayed.

Now I remember discussing this issue in Japan.  However, I can't
recall the exact scenario in which the delay occured.

Is the issue with the link status going down on the real device,
or the real device coming up?

IIRC we already have mechanisms in place to ensure that down
events
are not delayed by linkwatch.  Of course it is possible that this
isn't working for some reason, or some other part of the system
is
causing the delay.

So please clarify the scenario for us Hayasaka-san.  Also please
let us know how you measured the delay.

Thanks,

This issue happens when the link status is going down on the real
device.

ex) A cable is broken, or is unplugged from a NIC.

I measured the delay using ioctl with SIOCGIFFLAGS from userspace
in order to check if there is a time-lag of the flag between vlan
and real devices.

Also, you can check it using a script below.

-------------------------
#!/bin/sh
t=0
while :
do
	echo $t; t=$((t+1))
	echo -n real; ifconfig RealDev | grep UP
	echo -n vlan; ifconfig VlanDev | grep UP
	sleep 0.2
done
-------------------------

The result is shown as follows.
It is observed that there is a time-lag of RUNNING status between
real and vlan devices.

Hi !

This reminds me some work done in linkwatch

Please take a look at commit e014debecd3ee3832e647 (linkwatch:
linkwatch_forget_dev() to speedup device dismantle)

And more generally, code in net/core/link_watch.c

Maybe the problem is specific to a ethernet driver. Some devices poll
for link changes, and also do a manual check when ioctl was done.
This was mostly typical of older hardware that did not have a PHY
interrupt.

Hmm, I just tried the script on my laptop, and reproduced the problem
with a tg3 driver, considered as a reference one ;)

the 'carrier is on' event is immediately present on both devices, but
the 'carrier is off' is delayed by one second.

09:00.0 Ethernet controller: Broadcom Corporation NetXtreme BCM5755M
Gigabit Ethernet PCI Express (rev 02)
	Subsystem: Dell Device 01f9
	Flags: bus master, fast devsel, latency 0, IRQ 45
	Memory at f1ef0000 (64-bit, non-prefetchable) [size=64K]
	Expansion ROM at <ignored> [disabled]
	Capabilities: <access denied>
	Kernel driver in use: tg3
	Kernel modules: tg3