The uevent handling in udevd is not cpu hungry.
So, let's increase the default number of workers per cpu.
This decrease the number of queued uevents.
Without this commit (children_max is 16 on my laptop)
```
$ journalctl -b -u systemd-udevd.service | grep reached | wc -l
1544
```
With this commit (children_max is 30 on my laptop)
```
$ journalctl -b -u systemd-udevd.service | grep reached | wc -l
7
```
During boot process, many worker processes are forked and killed.
To decrease cycles of forking and killing worker, let's wait
3 seconds before killing workers. If new uevent or inotify event
comes within the delay, the killing porcess will be cancelled.
sysctl is disabled for /proc mounted from an user namespace thus entries like
/proc/sys/net/unix/max_dgram_qlen do not exist. In this case, skip the error
and do not try to change the default for the AF_UNIX datagram queue length.
It's not entirely impossible to screw something up playing with
kernel modules on a Saturday evening :-) This PR fixes a scenario
where a module has been loaded into the kernel but the module itself
has been removed from the disk.
```
$ lsmod | grep wireg
wireguard 225280 0
ip6_udp_tunnel 16384 1 wireguard
udp_tunnel 16384 1 wireguard
$ modprobe wireguard
modprobe: FATAL: Module wireguard not found in directory /lib/modules/4.18.16-200.fc28.x86_64
$ sudo ./systemd-networkd-tests.py NetworkdNetDevTests.test_wireguard
...
modprobe: FATAL: Module wireguard not found in directory /lib/modules/4.18.16-200.fc28.x86_64
test_wireguard (__main__.NetworkdNetDevTests) ... unexpected success
----------------------------------------------------------------------
Ran 1 test in 5.152s
FAILED (unexpected successes=1)
```
This is a follow-up to https://github.com/systemd/systemd/pull/10625.
A simple copy+paste mistake, since the reference to
systemd-localed.service was added to both locale.conf(5) and
vconsole.conf(5) in the same commit (8968e36f21).
After ec6a47044a, networkd starts
soon after removing links used by previous test. That causes
some racy situation of removing links and detecting links by networkd.
Yu Watanabe
Lennart Poettering
Tobias Jungel
Giuseppe Scrivano
Evgeny Vereshchagin
Lucas Werkmeister