CPU load on FreeBSD. Classic NTP 5-6% vs NTPsec 10-17%

Mike Yurlov ntp at kaluga.net
Fri Dec 13 08:31:14 UTC 2019

Hi All!

I recently started the public server for ntppool (Yo, Ask) on FreeBSD. 
Yesterday I was migrate from Classic NTPd to NTPSec (oh, it was 
painful!). I'm copy ntp.conf to ntpsec.conf and only convert "magic" 
127.127.20 x to refclock. When I looking to "top" I see NTPsec eat 
10-17% CPU. But Classic NTPd eat only 4-6% on same average 
3-4kpps/queries per second. Why?

System is FreeBSD 12.1-STABLE r353872, kernel compiled with options 
PPS_SYNC. Hardware is not new (but overhead for single ntpd) - 1RU MSI 
server with 6Gb memory and Intel(R) Core(TM)2 Quad CPU Q9400 @2.66GHz. 
1) uBlox 8 GPS+GLONASS on RS232 + PPS (primary and prefer)
2) Garmin 18x LVC on RS232 (backup and "noselect" because it have big 
jitter and does not have GLONASS)
3) some ntp Stratum1 servers

Classic NTPd is from BSD distribution/sources, version 4.2.8p13. NTPSec 
is 1.1.8 from .tar.gz.

I'm copy ntp.conf to ntpsec.conf and only convert "magic" 127.127.20 x to

refclock nmea unit 0 prefer mode 0x10000 minpoll 2 maxpoll 4 time2 
0.1782 refid GPS path /dev/gps0 baud 9600 flag1 1 flag2 0 flag3 1
refclock nmea unit 1 noselect mode 0x10000 minpoll 4 maxpoll 4 time2 
0.542 refid GPS path /dev/gps1 baud 4800 flag1 0 flag2 0 flag3 1

and run daemon as ntp -c ntpsec.conf

I read some topics/issues and suggest "server have many bad/flood 
queries (i'ts true, I'm inspecting traffic dump), so let's increase mru 
size?". Ok, I have 6Gb memory and powerfull CPU (for one ntpd task), 
therefore I' configure (values from some ntpsec issue topic):

mru initmem 100000 maxmem 250000 maxage 90000 minage 3600 incmem 1000

strange, but when I restart daemon, I does not see ~100M memory in 
ps/top output, only ~20M as usual and it increased slowly. After that I 
went to bed and ~7 hours later in the morning I have ~100Mb memory and 
68-70% ntpd CPU in "top". WOW! (I met similar behavior in very old 
traffic collecting daemons that use linear ip search in arrays without 

I comment mru settings and now have 12-17% again. It's 2x times more 
then Classic. NTPSec positioned as an improved alternative to the 
classic NTPd with code cleaning and optimization. Why so much CPU?


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