[systemd-devel] Improving module loading

[Tom Gundersen]

On Tue, Dec 23, 2014 at 12:25 PM, Hoyer, Marko (ADITG/SW2)
<mhoyer at de.adit-jv.com> wrote:
> Some numbers to the above mentioned arguments:
> - in an idle system, systemd-udev-trigger.service takes by about 150-200ms just to get the complete device tree to send out "add" uevents again (udevd was deactivated while doing this measure)

I'm working on optimizing this a bit (though we are obviously talking
about percentage points, not orders of magnitude). I'd be interested
in seeing if it could be further optimized to help your usecase once I
have pushed out the basic rework.

> - the processing of the resulting uevents by udevd takes 1-2 seconds (with the default rule set) again in an idle system

I haven't looked at this much recently, but if you find any
bottlenecks, do shout so we can look at improving it if possible.

> - in a general solution, we'd need to wait for udevd to completely settle until we can start using the devices

Hm, I would question this. In a semi-modern system you should not need
to wait for settle at all, as everything should be hotplug capable. If
you are in total control of your software (which I assume you are),
you should be able to fix the non-hotplug capable software and drop
the settling. Have you tried this? What is the blocker here?

If you drop settling, then I guess the biggest tweak you can do is
with the order in which devices are triggered. I'm not seeing how we
can do something sensible about this in a generic fashion, but might
be worth fiddling with to figure out what is the optimal order on your
system (to have a baseline for future optimizations).

Cheers,

Tom