H/W: Raspberry Pi 3 Model B Plus Rev 1.3
Activity LED configured to show cpu activity (default is io)
O/S: Raspian-lite bulls-eye
Pi-Hole:
Core version is v6.1.4 (Latest: v6.1.4)
Web version is v6.2.1 (Latest: v6.2.1)
FTL version is v6.2.3 (Latest: v6.2.3)
Upstream DNS is unbound, in same system.
Actual Behaviour
On the R-P which hosts Pi-Hole I have the "active" LED configured to show cpu activity. Since upgrading to Pi-Hole V6 this LED is showing a very faint green pulse about every second when system is idle. If Pi-Hole is stopped this pulse does not occur.
Pulse is also absent if LED is configured to its default of showing io activity.
top/htop is showing pihole-FTL process averaging 0.7-1.0% CPU in an idle system. Again, this differs from the V5 case where the process was typically 0%.
What is V6 pihole-FTL doing every second, and is it really necessary to do it so frequently?
I would guess that this is due to the new architecture in FTL v6. It now includes an API, which replaces lighttpd and php, and handles some stuff server-side. In exchange, you no longer have lighttpd or php consuming any CPU via Pi-hole, as well as reduced client-side usage to render the Query Log.
Here are the release notes including links to the detailed notes for each component. These include some CPU-related tweaks.
Thanks, chrislph, I'm sure you're right - the symptom is new since I upgraded to V6 and nothing else significant changed in the pihole environment. I can't see anything obvious in the release notes - may need a developer to assuage my curiosity about this.
PS My suspicion is that this is connected with V6 pihole automatically picking up changes made to config files be e.g. manual edits, which from experiments seems to happen very quickly.