Time issues on Linux

[Ralph Lange <ralph.lange@gmx.de>]

Dear Core,

We recently ran into an issue that others might have experienced before: [1]

Calling time functions that honour timezones - e.g. mktime() or 
localtime() - causes filesystem reads when accessing the timezone 
information. In setups where these functions are being called from 
driver threads in possibly fast loops (in our case converting time 
stamps from incoming PLC data packets) this easily leads to congestion 
and jitter in the 10s of millisecond range. (Connecting an IOC to 10 
PLCs with fast updates caused the system to completely overload and come 
close to a standstill, with TCP buffers overflowing and constant 350% 
CPU utilization on a 4 core VM.)
In libCom/osi's epicsTime module, I see epicsTimeToTM() and 
epicsTimeToGMTM() methods that allow to select if the timezone mechanism 
should be used or not.
However, the other direction only offers epicsTimeFromTM() that honors 
timezones, and eventually calls mktime().
Would you agree that epicsTimeFromGMTM() and the matching 
epicsTime::epicsTime(const gm_tm_nano_sec &tm) should be added?
Thanks for your help,
~Ralph

[1] See also https://rachelbythebay.com/w/2013/06/11/time/