[libvirt-users] e1000 network interface takes a long time to set the link ready

[Laine Stump]

On 05/10/2018 02:53 PM, Ihar Hrachyshka wrote:
> Hi,
> 
> In kubevirt, we discovered [1] that whenever e1000 is used for vNIC,
> link on the interface becomes ready several seconds after 'ifup' is
> executed

What is your definition of "becomes ready"? Are you looking at the
output of "ip link show" in the guest? Or are you watching "brctl
showstp" for the bridge device on the host? Or something else?

> which for some buggy images like cirros may slow down boot
> process for up to 1 minute [2]. If we switch from e1000 to virtio, the
> link is brought up and ready almost immediately.
> 
> For the record, I am using the following versions:
> - L0 kernel: 4.16.5-200.fc27.x86_64 #1 SMP
> - libvirt: 3.7.0-4.fc27
> - guest kernel: 4.4.0-28-generic #47-Ubuntu
> 
> Is there something specific about e1000 that makes it initialize the
> link too slowly on libvirt or guest side? 

There isn't anything libvirt could do that would cause the link to
IFF_UP up any faster or slower, so if there is an issue it's elsewhere.
Since switching to the virtio device eliminates the problem, my guess
would be that it's something about the implementation of the emulated
device in qemu that is causing a delay in the e1000 driver in the guest.
That's just a guess though.

>
> [1] https://github.com/kubevirt/kubevirt/issues/936
> [2] https://bugs.launchpad.net/cirros/+bug/1768955

(I discount the idea of the stp delay timer having an effect, as
suggested in one of the comments on github that points to my explanation
of STP in a libvirt bugzilla record, because that would cause the same
problem for e1000 or virtio).

I hesitate to suggest this, because the rtl8139 code in qemu is
considered less well maintained and lower performance than e1000, but
have you tried setting that model to see how it behaves? You may be
forced to make that the default when virtio isn't available.

Another thought - I guess the virtio driver in Cirros is always
available? Perhaps kubevirt could use libosinfo to auto-decide what
device to use for networking based on OS.