[systemd-devel] preset activation on first boot takes too long

[Dimitri John Ledkov]

Heya,

I'm looking at bootcharts and it seems like first boot preset
activation takes too much time...

So at the moment, we iterate all units, then iterate through presets
until we find a match and act upon it.

However, most distros have "disable *" as their last setting, or don't
use presets at all.

Furthermore looking at a fully featured system (e.g. my ubuntu laptop):
* 158 files do not have install section
* 89 have an install secion

Also it seems odd to have all of this in the pid one critical path ->
e.g. these things are being parsed before anything happens.

Thus I wonder if the presets should be moved into e.g. a generator
that will do the following on first boot only:

* parse .preset files
* construct list of things to enable
* enable all the units in that list

This should cut I/O and processing time at first boot by a bit, since
only the units to be activated will be parsed.

That also kind of means that it will only work if the last fallback
policy is "disable *".

For a reference, preset enabling on first boot accounts for around
6.5% of the first boot time for me on fairly minimal containers / base
VMs.

What do you think about this?

-- 
Regards,

Dimitri.
Pura Vida!

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