In order to find out why my home automation machine was running hot, I did some power profiling with powertop, top and iostat, and I noticed that the deCONZ binary was doing approximately 300 wakeups per second. This is the sort of thing that indicates a lot of frequent messages being processed.
I did some digging with strace and discovered that there is a ppoll() call being done every 0.003 seconds, the call looks like this:
ppoll([{fd=25, events=POLLIN}], 1, {tv_sec=0, tv_nsec=3000000}, NULL, 8) = 0 (Timeout)
In english this means: “Check to see if there’s data waiting on file descriptor 25, but return after 0.003 seconds” - and this is probably the source of the majority of the wakeups that deCONZ is doing.
If this polling interval were increased: even by a factor of 10 - to allow whatever else this polling loop processing is doing, no appreciable human latency would be introduced (there’s no other I/O happening on that thread), and CPU + heat + context switching could be reduced considerably.
This is just a guess based on strace data, it’s entirely possible there’s other considerations and the 0.003 second timeout is necessary for reasons I don’t understand. I don’t seem to have access to this source code so I can’t check.