Re: [patch v0] qapi/qmp: Add timestamps to qmp command responses.

[Roman Kagan]

On Tue, Sep 27, 2022 at 08:04:11AM +0200, Markus Armbruster wrote:
> Daniel P. Berrangé <berrange@redhat.com> writes:
> > On Mon, Sep 26, 2022 at 12:59:40PM +0300, Denis Plotnikov wrote:
> >> Example of result:
> >> 
> >>     ./qemu/scripts/qmp/qmp-shell /tmp/qmp.socket
> >> 
> >>     (QEMU) query-status
> >>     {"end": {"seconds": 1650367305, "microseconds": 831032},
> >>      "start": {"seconds": 1650367305, "microseconds": 831012},
> >>      "return": {"status": "running", "singlestep": false, "running": true}}
> >> 
> >> The responce of the qmp command contains the start & end time of
> >> the qmp command processing.
> 
> Seconds and microseconds since when?  The update to qmp-spec.txt should
> tell.
> 
> Why split the time into seconds and microseconds?

This is exactly how timestamps in QMP events are done, so we thought
we'd just follow suit

> > The mgmt app already knows when it send the QMP command and knows
> > when it gets the QMP reply.  This covers the time the QMP was
> > queued before processing (might be large if QMP is blocked on
> > another slow command) , the processing time, and the time any
> > reply was queued before sending (ought to be small).
> >
> > So IIUC, the value these fields add is that they let the mgmt
> > app extract only the command processing time, eliminating
> > any variance do to queue before/after.

Right, this is precisely the motivation.

Thanks,
Roman.