timerfd question

[Ken Brown]

This question is almost certainly too vague to be answerable, but I'll try 
anyway.  Is there any obvious reason that it's bad to have two timers running 
simultaneously, one using timerfd (started via timerfd_settime) and one using a 
POSIX timer (started via timer_settime)?

Here's the context: Emacs runs timers.  Until recently it used timerfd if 
available, and otherwise a POSIX timer.  After a recent change, it starts both 
kinds of timers.  This causes a severe slowdown on Cygwin 
(https://debbugs.gnu.org/cgi/bugreport.cgi?bug=51734#32).  The easiest thing is 
just to disable that change on Cygwin, but I'd feel better understanding why 
this is a problem.

Ken