Re: [PATCH v6] can: virtio: Add virtio CAN driver

[Matias Ezequiel Vara Larsen <mvaralar@redhat.com>]

On Mon, Dec 29, 2025 at 09:55:50PM +0100, Francesco Valla wrote:
> Hi Matias,
> 
> On Mon, Dec 29, 2025 at 07:53:48PM +0100, Matias Ezequiel Vara Larsen wrote:
> > > While stress testing this, I noticed that flooding the virtio-can
> > > interface with packets leads to an hang of the interface itself.
> > > I am seeing this issuing, at host side:
> > > 
> > > 	while true; do cansend can0 123#00; done
> > > 
> > > with:
> > > 
> > >  - QEMU: the tip of the master branch plus [2]
> > >  - vhost-device: the tip of the main branch
> > > 
> > > and the following QEMU invocation:
> > > 
> > > qemu-system-x86_64 -serial mon:stdio \
> > >     -m 2G -smp 2 \
> > >     -kernel $(pwd)/BUILD.bin/arch/x86/boot/bzImage \
> > >     -initrd /home/francesco/SRC/LINUX_KERNEL/initramfs.gz \
> > >     -append "loglevel=7 console=ttyS0" \
> > >     -machine memory-backend=pc.ram \
> > >     -object memory-backend-file,id=pc.ram,size=2G,mem-path=/tmp/pc.ram,share=on \
> > >     -chardev socket,id=can0,path=/tmp/sock-can0 \
> > >     -device vhost-user-can-pci,chardev=can0
> > > 
> > > 
> > > Restarting the interface (i.e.: ip link set down and the up) does not
> > > fix the situation.
> > > 
> > > I'll try to do some more testing during the next days.
> > 
> > I tried this and I could not reproduce it. [2] requires a minimal change
> > to apply, i.e., qdev-properties.h has changed to /core. I'll send a v2
> > for that. I used latest vhost-device-can. I run `candump can0` in the
> > guest and `while true; do cangen vcan0; done` in the host. Am I missing
> > something?
> 
> With the plain 'cangen' you are not really flooding the interface, since
> you are only sending a random CAN frame every 200ms. The only way I can
> reproduce this behaviour in a consistent manner is running from the host:
> 
>     while true; do cansend vcan0 134#00; done
> 
> which seems to generate the maximum amount of traffic.
> 
You were right. I could reproduce it. After a while, I stop to get packets
in the guest. I'll investigate.

Thanks.