I'm not sure if it's just me, but I found the lack of reference to system time interesting. Maybe it's one those things everyone does (but never talks about), but if you're logging, one of the absolute performance killers can actually turn out to be getting the system time via gettimeofday() or whatever. That's a syscall which involves a context switch, which... (It goes downhill from there.)

Much better to just get the time every once in a while and cache it.