[systemd-devel] Adopt processes spawned before /lib/systemd/systemd takes over as PID 1?

[Cristian Rodríguez]

On Fri, Apr 17, 2015 at 4:06 PM, Matt Hoosier <matt.hoosier at gmail.com> wrote:
> On Fri, Apr 17, 2015 at 12:22 PM, Lennart Poettering
> <lennart at poettering.net> wrote:
>>
>> On Fri, 17.04.15 09:00, Matt Hoosier (matt.hoosier at gmail.com) wrote:
>>
>> > Hi,
>> >
>> > I'm writing to see whether there's a "best" way to allow systemd to
>> > inherit
>> > ownership of a process forked from a hand-crafted /sbin/init process
>> > before
>> > that hand-crafted process turns over the keys to systemd by doing
>> > exec("/lib/systemd/systemd") over the top of itself and allowing it to
>> > take
>> > over as PID 1.
>>
>> We support this only really for "kernel-like" processes that are
>> started from the initrd, and basically run as long as the system is up
>> without every being restarted in between, thus effectively appearing
>> much like a kernel process and nothing systemd should
>> manage. Processes like this should be marked with argv[0][0] = '@',
>> see for details:
>>
>> https://wiki.freedesktop.org/www/Software/systemd/RootStorageDaemons/
>>
>> > I know that sounds like an odd thing to ask about. The use-case has to
>> > do
>> > with being able to start some work extremely early during boot of
>> > embedded
>> > systems to achieve performance goals. I don't wish to subvert systemd,
>> > and
>> > in fact would love for systemd to be able to monitor the process, stop
>> > it,
>> > restart according to the normal [Service] configuration in a unit file
>> > describing the process.
>>
>> Hmm, are you sure that invoking the binary from systemd as first
>> service is really that much slower than starting systemd only afterwards?
>
>
> The bootcharting that I do seems to show that about 1.2 - 1.5 sec are spent
> internal to systemd before any external processes get run for the particular
> embedded CPU I'm using. That gap is a killer at the moment.

Did you watch this presentation ?

https://www.youtube.com/watch?v=RFVlbaDqll8

what part of systemd is taking 1.5 seconds to start, on what CPU and
how much of RAM does the board has ?