[virtio-dev] Re: About custom device counter

Michael S. Tsirkin
2023-06-12T06:25:52Z

On Mon, Jun 12, 2023 at 02:12:35PM +0800, Xuan Zhuo wrote:
> We hope to support device custom counter. That is, virtio spec provides a
> channel for driver and device, and both key and value are provided by device.
>
> We discussed this issue earlier, and after some internal practice, I think it is
> still necessary to discuss this again.
>
> It is very important, each cloud vendor will always have some special counters,
> these counters may not exist in another vendor. At the same time, if we have
> to discuss it in the spec every time we add a counter, or add a feature, I
> think it is very inconvenient. Manufacturers may add some new counters at any
> time based on some new requirements. Some counters may also be removed at any
> time.
>
> Of course I know that doing this might hurt migration. But what I want to say is,
> why does it affect live migration? These counters we plan to give to users
> through ethtool -S, and some changes have taken place in the ethtool counters
> output by users. Does this have any practical impact? Or do we directly use
> some other output in a way, we can clearly tell the user that these counters
> may change during the migration process. For example, the driver is migrated
> to some new devices. These devices support some new counters. I think users
> should be able to see these new counters. These new counters may be the
> purpose of the migration.
>
> We don't need to support live migration at this point.
>
> Thanks.

Why not just document the thing?

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MST