Re: virtio_net: Almost a second until link becomes ready

Re: virtio_net: Almost a second until link becomes ready

[Michael S. Tsirkin]

On Tue, May 04, 2021 at 08:04:50PM +0200, Paul Menzel wrote:
> Dear VirtIO net driver folks,
> 
> 
> I would like to start the video conferencing software Jitsi in a QEMU/KVM VM
> as quickly as possible.
> 
> ```
> $ qemu-system-x86_64 --version
> QEMU emulator version 5.1.0
> Copyright (c) 2003-2020 Fabrice Bellard and the QEMU Project developers
> $ qemu-system-x86_64 -enable-kvm -name jitsi -cpu host -m 8G -smp 12 -global
> virtio-net-pci.romfile= -device virtio-rng-pci -boot menu=off -drive
> file=jitsi.003.disk,format=qcow2,if=virtio -nic tap,ifname=tap.jitsi,script=/bin/true,downscript=/bin/true,model=virtio-net-pci,mac=52:c6:11:00:00:18
> -vnc :60 -k de -serial none -chardev
> socket,id=mon1,path=mon.socket,server,nowait -chardev
> socket,id=mon2,path=qmp.socket,server,nowait -mon chardev=mon1,mode=readline
> -mon chardev=mon2,mode=control
> ```
> 
> The (inaccurate) measurement with `systemd-analyze critical-chain` shows
> that `systemd-network-wait-online.service` takes some time.
> 
>           └─systemd-networkd-wait-online.service @159ms +2.871s
> 
> Linux logs:
> 
>     [    1.058253] virtio_net virtio0 ens3: renamed from eth0
>     […]
>     [    1.103165] IPv6: ADDRCONF(NETDEV_UP): ens3: link is not ready
>     […]
>     [    2.044947] IPv6: ADDRCONF(NETDEV_CHANGE): ens3: link becomes ready
> 


I'm not sure what is going on here: a lost config interrupt?
systemd forcing link down then up for its own reasons?
But a possible workaround is
to add status=off to the virtio net device to force link to always
be up.

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