Re: [virtio-dev] Dirty Page Tracking (DPT)

[Eugenio Perez Martin <eperezma@redhat.com>]

On Tue, Apr 7, 2020 at 12:28 PM Rob Miller <rob.miller@broadcom.com> wrote:
>
> Does this mean that SW takes over the datapath during LM?

"Takes over" sounds to me like solving the problem using failover to
switch to a software interface to do the packet forwarding during
migration [1]. In this solution, only the used ring needs to be spied
or intercepted to communicate qemu the memory regions modified.

Not sure if this is what you had in mind.

[1] https://www.dpdk.org/wp-content/uploads/sites/35/2019/10/VirtioNet.pdf

> If so, is there any infrastructure to "gracefully" do a hand-off from HW mode (pci device is managing the rings) to SW mode, in that when switching from HW->SW, HW is stalled & quiesced, then the SW takes from where HW left off?
>
> Rob Miller
> rob.miller@broadcom.com
> (919)721-3339
>
>
> On Tue, Apr 7, 2020 at 5:53 AM Eugenio Perez Martin <eperezma@redhat.com> wrote:
>>
>> Hi!
>>
>> So, from the previous mails, it seems that monitoring the used ring
>> (and the packed descriptors) is a good first step in that direction,
>> as DPDK did. This way, the device does not need to worry about the
>> dirty page tracking using a bitmap and the PCI writes limitation, and
>> we can evaluate later the proposed alternatives:
>> * Alternate used descriptors in packed.
>> * vDPA interface for vDPA devices in a convenient format.
>>
>> Any thoughts? Do you think that we should start with another way?
>>
>> Thanks!
>>