Re: [PATCH v3 6/8] admin: Add theory of operation for write recording commands

[Jason Wang <jasowang@redhat.com>]

On Thu, Nov 16, 2023 at 1:51âPM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Thu, Nov 16, 2023 at 05:29:54AM +0000, Parav Pandit wrote:
> > We should expose a limit of the device in the proposed WRITE_RECORD_CAP_QUERY command, that how much range it can track.
> > So that future provisioning framework can use it.
> >
> > I will cover this in v5 early next week.
>
> I do worry about how this can even work though. If you want a generic
> device you do not get to dictate how much memory VM has.
>
> Aren't we talking bit per page? With 1TByte of memory to track ->
> 256Gbit -> 32Gbit -> 8Gbyte per VF?
>
> And you happily say "we'll address this in the future" while at the same
> time fighting tooth and nail against adding single bit status registers
> because scalability?
>
>
> I have a feeling doing this completely theoretical like this is problematic.
> Maybe you have it all laid out neatly in your head but I suspect
> not all of TC can picture it clearly enough based just on spec text.
>
> We do sometimes ask for POC implementation in linux / qemu to
> demonstrate how things work before merging code. We skipped this
> for admin things so far but I think it's a good idea to start doing
> it here.

+1

Most virtio features were developed in this way. It's cheap and easy
to find issues in both design and implementation.

Another non virtio example, that is the rocker switch which is
prototyped in Qemu for switchdev.

>
> What makes me pause a bit before saying please do a PoC is
> all the opposition that seems to exist to even using admin
> commands in the 1st place. I think once we finally stop
> arguing about whether to use admin commands at all then
> a PoC will be needed before merging.

Exactly.

Thanks

>


>
> --
> MST
>