Re: [PATCH RFC 04/15] KVM: Implement ring-based dirty memory tracking

Michael S. Tsirkin
2019-12-10T21:49:12Z

On Tue, Dec 10, 2019 at 02:31:54PM +0100, Paolo Bonzini wrote:
> On 10/12/19 14:25, Michael S. Tsirkin wrote:
> >> There is no new infrastructure to track the dirty pages---it's just a
> >> different way to pass them to userspace.
> > Did you guys consider using one of the virtio ring formats?
> > Maybe reusing vhost code?
>
> There are no used/available entries here, it's unidirectional
> (kernel->user).

Didn't look at the design yet, but flow control (to prevent overflow)
goes the other way, doesn't it? That's what used is, essentially.

> > If you did and it's not a good fit, this is something good to mention
> > in the commit log.
> >
> > I also wonder about performance numbers - any data here?
>
> Yes some numbers would be useful. Note however that the improvement is
> asymptotical, O(#dirtied pages) vs O(#total pages) so it may differ
> depending on the workload.
>
> Paolo