Re: [PATCH 0/5] migration: Downtime observability improvements

[Joao Martins]

On 04/10/2023 18:19, Peter Xu wrote:
> On Tue, Sep 26, 2023 at 05:18:36PM +0100, Joao Martins wrote:
>> For now, mainly precopy data, and here I added both tracepoints and
>> QMP stats via query-migrate. Postcopy is still missing.
> 
> IIUC many of those will cover postcopy too, but not all?
> 
> I think the problem is postcopy didn't update downtime_start, however it
> updates MigrationState.downtime, and probably we can start to keep it more
> like precopy, e.g., in postcopy_start(), where downtime_start can be
> time_at_stop (or it can be more accurate; now it's probably fetching the
> timestamp too early).
> 
Good point!

> Basically if we want to expose anything, especially some qapi object, IMHO
> we'd better make it work for both pre/post copy because otherwise it'll be
> hard for mgmt app to know which qemu supports precopy only, and which
> support both (if we'll add that for postcopy too).
> 

Yeap, I totally agree.