smf

Prometheus can add latency to the data path.

Use a low priority scheduling group for the metrics.

ref: https://groups.google.com/forum/#!topic/seastar-dev/adKyzRgqc5E

> with_scheduling_group(maintenance_scheduling_group, [&] { 
>                   return 
> prometheus_server.listen(ipv4_addr{prom_addr.addr_list.front(), 
> pport}).handle_exception([pport, &cfg] (auto ep) { 
>  

Description

I have a very large smf 1.1.21 forum of over 1.5 million users. I know I should've upgraded awhile ago due to security risks etc. However, I have been very lazy. I kinda got some energy lately to redo my old theme into the new SMF 2.1 latest (github) version and fina