Here is a ping from my Raspberry Pi with Home Assistant to my router over Wifi:
64 bytes from 192.168.42.1: icmp_seq=1 ttl=64 time=16.8 ms
64 bytes from 192.168.42.1: icmp_seq=2 ttl=64 time=81.5 ms
64 bytes from 192.168.42.1: icmp_seq=3 ttl=64 time=11.1 ms
64 bytes from 192.168.42.1: icmp_seq=4 ttl=64 time=4.76 ms
64 bytes from 192.168.42.1: icmp_seq=5 ttl=64 time=126 ms
64 bytes from 192.168.42.1: icmp_seq=6 ttl=64 time=72.1 ms
64 bytes from 192.168.42.1: icmp_seq=7 ttl=64 time=1029 ms
64 bytes from 192.168.42.1: icmp_seq=8 ttl=64 time=689 ms
64 bytes from 192.168.42.1: icmp_seq=9 ttl=64 time=157 ms
64 bytes from 192.168.42.1: icmp_seq=10 ttl=64 time=4.61 ms
64 bytes from 192.168.42.1: icmp_seq=11 ttl=64 time=396 ms
64 bytes from 192.168.42.1: icmp_seq=12 ttl=64 time=105 ms
64 bytes from 192.168.42.1: icmp_seq=13 ttl=64 time=21.0 ms
64 bytes from 192.168.42.1: icmp_seq=14 ttl=64 time=1.79 ms
64 bytes from 192.168.42.1: icmp_seq=15 ttl=64 time=79.4 ms
64 bytes from 192.168.42.1: icmp_seq=16 ttl=64 time=2281 ms
64 bytes from 192.168.42.1: icmp_seq=17 ttl=64 time=2410 ms
64 bytes from 192.168.42.1: icmp_seq=18 ttl=64 time=1387 ms
64 bytes from 192.168.42.1: icmp_seq=19 ttl=64 time=878 ms
64 bytes from 192.168.42.1: icmp_seq=20 ttl=64 time=487 ms
64 bytes from 192.168.42.1: icmp_seq=21 ttl=64 time=153 ms
load average: 0.09, 0.21, 0.29
This problem started when I added -v /run/dbus:/run/dbus:ro to my docker command line, which now reads:
docker run -d \
--name homeassistant \
--privileged \
--restart=unless-stopped \
-e TZ=Europe/Berlin \
-v /opt/homeassistant/config:/config \
-v /run/dbus:/run/dbus:ro \
--network=host \
ghcr.io/home-assistant/raspberrypi4-homeassistant:stable
Here’s a ping after I removed the line and restarted HA:
64 bytes from 192.168.42.1: icmp_seq=1 ttl=64 time=1.47 ms
64 bytes from 192.168.42.1: icmp_seq=2 ttl=64 time=1.41 ms
64 bytes from 192.168.42.1: icmp_seq=3 ttl=64 time=5.20 ms
64 bytes from 192.168.42.1: icmp_seq=4 ttl=64 time=12.5 ms
64 bytes from 192.168.42.1: icmp_seq=5 ttl=64 time=1.39 ms
64 bytes from 192.168.42.1: icmp_seq=6 ttl=64 time=1.48 ms
64 bytes from 192.168.42.1: icmp_seq=7 ttl=64 time=1.66 ms
64 bytes from 192.168.42.1: icmp_seq=8 ttl=64 time=1.97 ms
64 bytes from 192.168.42.1: icmp_seq=9 ttl=64 time=4.12 ms
64 bytes from 192.168.42.1: icmp_seq=10 ttl=64 time=1.29 ms
64 bytes from 192.168.42.1: icmp_seq=11 ttl=64 time=1.43 ms
64 bytes from 192.168.42.1: icmp_seq=12 ttl=64 time=5.38 ms
64 bytes from 192.168.42.1: icmp_seq=13 ttl=64 time=1.48 ms
64 bytes from 192.168.42.1: icmp_seq=14 ttl=64 time=25.2 ms
64 bytes from 192.168.42.1: icmp_seq=15 ttl=64 time=35.5 ms
64 bytes from 192.168.42.1: icmp_seq=16 ttl=64 time=1.82 ms
64 bytes from 192.168.42.1: icmp_seq=17 ttl=64 time=1.52 ms
64 bytes from 192.168.42.1: icmp_seq=18 ttl=64 time=0.976 ms
64 bytes from 192.168.42.1: icmp_seq=19 ttl=64 time=1.20 ms
64 bytes from 192.168.42.1: icmp_seq=20 ttl=64 time=29.9 ms
load average: 0.45, 0.52, 0.39
It doesn’t seem to be purely a CPU issue, I have added load averages to the listings above. (They are from different times after HA startup, I just wanted to demonstrate that the load isn’t higher with the mount.) HA doesn’t show up in top particularly different with and without the mount either.
It’s a Raspberry Pi 4 Model B Rev 1.4, so 4 cores.
I can reliably reproduce this, as soon as I add the mount, the spikes begin, when I remove it, they go away. In fact I can tell whether the dbus directory is mounted or not just by looking at the ping. 
The spikes do not coincide with SD card throughput as reported by iostat. The SD card is mostly idle.