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

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

On Mon, 19 Jun 2023 10:25:38 -0400, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> On Thu, Jun 15, 2023 at 02:23:31PM +0800, Xuan Zhuo wrote:
> > On Tue, 13 Jun 2023 05:02:01 -0400, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > > On Mon, Jun 12, 2023 at 07:27:15PM +0800, Xuan Zhuo wrote:
> > > > On Mon, 12 Jun 2023 02:25:42 -0400, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > > > > 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?
> > > >
> > > > Device Counter or Device Stat, we discussed this issue earlier,
> > > > So I want to slove the problem migration firstly.
> > > >
> > > >
> > > > Thanks.
> > >
> > > Sorry have trouble parsing this.
> > >
> > > Can we get examples of counters from various vendors, so that
> > > it's clear what kind of thing this, and it becomes convincing
> > > that abstracting this in virtio spec is pointless?
> >
> > 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.
> >
> >
> > Such as "session", our dpu supports tcp connection tracking, but there is an
> > upper limit to the number of connections, and if it exceeds, packet loss will
> > also occur.
> >
> > These are two commonly used scenarios, I hope they can help you.
> >
> > Thanks.
>
>
> So not a counter at all really. More a capability.

Explain in other mail.

>
> My rule of thumb is that if something can be relevant to multiple
> vendors then it should not be a vendor specific capaiblity.
> What you have described can easily apply to a software
> virtio imlementation, so it's relevant for multiple
> vendors.

Great!!

>
> So please try to add this to the spec as a generic capability.
> Yes adding vendor specific extensions is of course less work
> for vendors. But the ecosystem is only strong if everyone is
> working on the same spec and codebase.

I agree.

Thank.


>
> >
> > >
> > > Also, am I right assuming that in virtualized settings this is mostly
> > > relevant for hosts? E.g. guests see a vendor neutral virtio but
> > > host wants to figure out source of issues?
> > >
> > >
> > >
> > >
> > > >
> > > > >
> > > > > --
> > > > > MST
> > > > >
> > > > >
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> > > > > OASIS Virtual I/O Device (VIRTIO) TC.
> > > > >
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>