[virtio-dev] RE: [virtio-comment] Re: About custom device counter

Parav Pandit
2023-06-19T12:33:40Z

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Friday, June 16, 2023 10:13 AM
> > Such as "limit", in a cloud scenario, multiple users purchase
> > different VMs, and these VMs share the capabilities of the same host.
> > In order to ensure that each VM will not affect others, the network
> > card(virtio-net) capability of each VM is limited. When these users purchase
> VMs, this limit has already been determined.
> > So if the network card traffic of a vm exceeds the upper limit, packet
> > loss will occur. It is necessary for us to count these packet losses.
> > And the device should expose to the user.
>
> OK so here, driver is expected to rate limit yes?
>
Some implementations of txq are lossy and some are not creating backpressure/flow control to driver so driver can rate limit it naturally.
So a tx packet drop counter is needed to cover the lossy implementations which is abstract enough regardless of reason on why device dropped it.
A more granular counter becomes vendor specific that we can possibly avoid or place under different command.