[systemd-devel] Improve boot-time of systemd

[Kay Sievers]

On Fri, Mar 18, 2011 at 14:40, Gustavo Sverzut Barbieri
<barbieri at profusion.mobi> wrote:
> On Fri, Mar 18, 2011 at 10:52 AM, Andrey Borzenkov <arvidjaar at mail.ru> wrote:
>> On Fri, Mar 18, 2011 at 12:35 PM, fykcee1 at gmail.com <fykcee1 at gmail.com> wrote:

>>> 1. What can readahead affect boot-time?
>>> Sadly observed negative affect -- boot-time increases at least 1s.
>>
>> From subjective feelings (no real measurements) I confirm it.
>
> I noticed it as well, even with my Macbook Pro i7 with 8Gb RAM and
> 128SSD using btrfs.

It's ~0.5 sec faster here with readahead on a SSD.

> But it could be improved yes. As you all said, maybe we should handle
> udev hotplug in a more throttled way by postponing non-critical
> devices and having everything else to be hotplug aware?

That's not really possible, you can not really make such list, and you
need to handle all parent devices from all 'interesting' devices
anyway to expose them.

The 'settle' service is only there for broken services. Originally it
wasn't even pulled into the base target but was free-hanging with
nobody getting blocked by it. Lennart pulled it in for a few broken
things and selinux to work, and it ended up blocking the base target
to be on the safe side for non-hotplug aware stuff. We might want to
re-check if that's really what we want.

Ideally, the entire 'settle' step would not even exist. I guess in
your limited environments, you can just drop the entire thing and let
the coldplug task run in the background.

Services need to cope with uninitialized devices then, and filter them
out when enumerating subsystems, and wait for the proper event from
udev. That should all be pretty straight-forward if you don't need to
support all the insanity in usual Linux distros.

Kay