Re: [PATCH v10] virtio-net: support device stats

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Mar 01, 2022 at 08:28:59PM +0800, Xuan Zhuo wrote:
> On Tue, 1 Mar 2022 07:25:16 -0500, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > On Tue, Mar 01, 2022 at 07:32:23PM +0800, Xuan Zhuo wrote:
> > >
> > > I have to say, this design is really good.
> > >
> > > I think one of the core points of your design is to separate drop stats, gso
> > > stats, etc. Get the stats you want based on negotiation and needs. And covering
> > > the control queue, I am very surprised.
> > >
> > > But does this design solve the problem of expansion? Various stats independent
> > > structures seem to be convenient for expansion. But is this expansion ready for
> > > dynamic negotiation?
> >
> > For negotiation, we can either separate feature flags for each supported
> > type, or do like RSS and add commands for querying supported types
> > and enabling stats collection. Features is probably easier
> > for now ... Also, do we need to enable/disable stat collection?
> 
> I think you mean dynamic enable/disable it. There is no such requirement in our
> environment. Since the statistical overhead is very small, I think there is no
> need to dynamically disable it.
> 
> But I thought it would be interesting to support clearing. It would be useful in
> some debugging scenarios. :)

clearing would then need to be atomic. how would userspace invoke it?
anyway, we can add this later.

> >
> >
> >
> > > My earliest solution is dynamic negotiation, that is, the driver tells the
> > > device how many stats it wants to get. And the device negotiates how many stats
> > > it should give to the driver based on this information of the driver.
> > >
> > > But that's not great for migration. So gave up.  @Jason
> >
> > Any optional feature is problematic for migration, at least with
> > features device knows ahead of the time what does driver
> > want to use.
> 
> 
> I want to make it clear that we will expand stats based on new features or new
> commands. So as long as we split up each stats for future expansion, it will be
> ok.
> 
> I will reorganize a copy based on your design and send it out tomorrow.
> 
> Thank you for your help and patience.
> 
> >
> > --
> > MST
> >