Re: [PATCH] virtio_net: Revert "virtio_net: set the default max ring size by find_vqs()"

[Andres Freund]

Hi,

On 2022-08-15 17:04:10 -0400, Michael S. Tsirkin wrote:
> So virtio has a queue_size register. When read, it will give you
> originally the maximum queue size. Normally we just read it and
> use it as queue size.
> 
> However, when queue memory allocation fails, and unconditionally with a
> network device with the problematic patch, driver is asking the
> hypervisor to make the ring smaller by writing a smaller value into this
> register.
> 
> I suspect that what happens is hypervisor still uses the original value
> somewhere.

It looks more like the host is never told about the changed size for legacy
devices...

Indeed, adding a vp_legacy_set_queue_size() & call to it to setup_vq(), makes
5.19 + restricting queue sizes to 1024 boot again.  I'd bet that it also would
fix 6.0rc1, but I'm running out of time to test that.

Greetings,

Andres Freund