Re: virtio_net: Almost a second until link becomes ready

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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