[systemd-devel] Grouping services in systemd..

[Lennart Poettering]

On Do, 02.04.20 18:51, nitish nagesh (nagesh.nitish at gmail.com) wrote:

> Hi folks,
>
>   We are working on an embedded ARM Cortex A9 based system (aka low CPU).
> It runs on a custom linux based operating system which uses systemd.
>
>   We have a bunch of daemons (around ~50+) that come up during boot
> simultaneously which slows down the boot significantly as the CPU runs out
> of breath. We were thinking of staggering these daemons into 2 groups. The
> first group containing "critical" daemons (around 15) so that they finish
> faster and make the system usable sooner. Followed by the second group of
> daemons.
>
>    Separating daemons into buckets could be done using:
> 1) systemd targets: Introduce 2 new targets and classify the
> services/daemons into them. Layer these targets during boot.
> 2) Cgroups: Create a new systemd slice and put all the "critical" services
> into it. Allocate sufficient CPUShares value to the slice so that this
> slice gets its due CPU% to finish faster boot.
>
> Can you please suggest which of the above is a better approach? Respective
> pros/cons with each.
>
> Or if there is a third approach better than the above?
>
> Thanks in advance,

StartupCPUWeight= and StartupIOWeight= are probably what you should be
using? Have you played around with that? That passes this problem on
to the CPU/IO schedulers of the kernels. i.e. you still enqueue
everything in parallel, but tell the kernel what to schedule first.

In recent systemd versions the weights configured this way also affect
the order in which jobs are dispatched by systemd itself if multiple
are runnable at the same time.

Lennart

--
Lennart Poettering, Berlin