[systemd-devel] Significant speedup of systemd boot time with CONFIG_HZ=1000

[Oester Jonas (CM-AI/PJ-CF31)]

> For a while, I was rather unhappy with the boot times I was seeing,
> but after changing CONFIG_HZ from 100 to 1000, that changed
> dramatically.

...

> There is also a rather peculiar delay between the startup of several
> services (dev-mqueue.mount, systemd-random-seed-load.service, etc)
> which is very regular.  Not sure why this happens.
> 
> Does anyone have any insights into why we have this huge difference?

CONFIG_PREEMPT is not enabled in your kernel configuration; in that case system performance is highly dependent on how often the scheduler runs (for some workloads at least). The delay between services most likely comes from the interaction between systemd and cgroup controllers (cf. http://0pointer.de/blog/projects/cgroups-vs-cgroups.html, which has further suggestions for how you might want to configure your kernel).

-- 
Jonas Öster 

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