[systemd-devel] Plot time data anomalies

[Lennart Poettering]

On Mi, 11.01.23 13:31, Lennart Poettering (lennart at poettering.net) wrote:

> On Mi, 11.01.23 11:53, Joshua Zivkovic (joshua.zivkovic at codethink.co.uk) wrote:
>
> > Hello,
> >
> > I've been working on adding JSON and table output to `systemd-analyze
> > plot`, to allow programmatic access to the data presented in the SVG
> > produced by `systemd-analyze plot`. Whilst using this data I have
> > noticed some irregularities in the initialisation times associated with
> > a variety of units. It seems as though these units are being activated,
> > deactivated and then reactivated because they have recorded
> > deactivation times that are before the recorded activation time.
> >
> > Looking at some of these units, they don't use the `Restart=`
> > configuration so it's unusual that they are seemingly being restarted.
> >
> > These irregularities are dealt with by forcing the values to some other
> > recorded value of that unit through a series of conditions in the SVG
> > production code.
> >
> > I'm interested in whether this means that the times for unit
> > initialisation, presented by `plot`, aren't entirely accurate and if
> > there is anything that can be done about this.
>
> You should read them with a grain of salt. And you should only run the
> tool shortly after booting (i.e. where there's a reasonably chance no
> service has been restarted yet). If you do it later then the data is
> going to be garbage because of the discrepancy between what we
> actually track (startup time of most recent invocation) to what people
> might expect (startup time of first invocation).
>
> Also note that services that are not referenced by anything (and
> didn't fail) might have been unloaded (i.e. "GC'ed"), which means
> their startup timing info is released and won't show up in the
> displayed data either.

I added some explanatory docs for this now, in this PR:

https://github.com/systemd/systemd/pull/26019

ptal

Lennart

--
Lennart Poettering, Berlin