[ntp:questions] Test ntpd performance

Dave Hart hart at ntp.org
Sat Sep 25 23:31:24 UTC 2010


On Fri, Sep 24, 2010 at 6:23 PM, R C <rc_work at yahoo.com> wrote:
> I want to test the performance of the ntpd server. Are there any free/open
> source ntp clients that measure the server scalability?

I don't know of any such scalability-testing client software, but I
can tell you ntpd scalability is typically a non-issue.  The traffic
involves small packets, which take very little time to process, so
typically you'll run into router scalability issues before server
ones.

I am involved with a publicly-accessible pool.ntp.org server running
on a 2.5 GHz Celeron.  It uses ntpd built without disabling ntpd's
built-in debugging support, though it is using compiler optimization,
it's also carrying around extra sanity-checking code and activity
tracing that is typically not enabled at runtime, but still causes
extra overhead compared to a ntpd configured with --disable-debugging.

Here's some hard data on its scalability:

hart at pool1> ps ax | fgrep ntpd
 3332  ??  Rs   193:57.22 /usr/local/bin/ntpd -c /etc/ntp.conf -g
 3333  ??  I      0:16.44 /usr/local/bin/ntpd -c /etc/ntp.conf -g
21884  p0  R+     0:00.00 fgrep ntpd
hart at pool1> ntpq -c sysstats
uptime:                 789921
sysstats reset:         789921
packets received:       181690517
current version:        115060504
older version:          50474534
bad length or format:   16152355
authentication failed:  369435
declined:               2605
restricted:             11647
rate limited:           15114153
KoD responses:          1291563
processed for time:     54715
hart at pool1>

There are two ntpd processes, the second is a DNS worker child of the
first.  Apparently there's a DNS name in its ntp.conf which isn't
resolving which it is continuing to retry occasionally.  In 789921s,
it has consumed 11654s of CPU time, or about 1.5%.  Undoubtedly
there's some system overhead not accounted for in that CPU time, but
you can see the CPU requirement to keep up with an average of 230
requests/s is marginal.  Its ntpd performance is great:


hart at pool1> ntpq -crv -p
associd=0 status=0618 leap_none, sync_ntp, 1 event, no_sys_peer,
version="ntpd 4.2.7p50 at 1.2188-o Thu Sep 16 19:45:06 UTC 2010 (3)",
processor="i386", system="FreeBSD/6.4-STABLE", leap=00, stratum=2,
precision=-20, rootdelay=1.637, rootdisp=10.881, refid=127.67.113.92,
reftime=d04902de.fb29a07c  Sat, Sep 25 2010 23:23:10.981,
clock=d0490453.ef2cc9cb  Sat, Sep 25 2010 23:29:23.934, peer=37589, tc=7,
mintc=3, offset=-0.035, frequency=-67.148, sys_jitter=0.831,
clk_jitter=0.092, clk_wander=0.001
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 192.168.4.255   .BCST.          16 B    -   64    0    0.000    0.000   0.001
-clock.sjc.he.ne .CDMA.           1 u    1  128  377    0.550   -1.135   1.203
+clock.fmt.he.ne .PPS.            1 u  122  128  377    1.092    0.015   0.056
*clock.fmt.he.ne .PPS.            1 u  108  128  377    1.637   -0.203   0.883
+clepsydra.dec.c .GPS.            1 u  116  128  377    0.679    0.017   0.015
+usno.pa-x.dec.c .USNO.           1 u  102  128  377    0.616    0.048   0.235
-psp-os1.ntp.org 192.168.4.22     3 s   63   64  376    0.111   -0.019   0.039
-clock.isc.org   .GPS.            1 u    7  128  377    0.228   -3.965   0.390
 149.20.54.20 (p 131.107.13.100   2 u  109  128  377    0.328    8.792   3.214
hart at pool1>

Would you mind elaborating on what question(s) you hope to answer
through testing?

Cheers,
Dave Hart



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