[ntp:questions] Test ntpd performance

Rick Jones rick.jones2 at hp.com
Mon Sep 27 19:21:50 UTC 2010

unruh <unruh at wormhole.physics.ubc.ca> wrote:
> The dominant rate limiter is the network-- even if you have a 1Gb
> network-- switches, interrupts, etc.

Including a 14 byte Ethernet header, an NTP query/response appears to
be 80 bytes or 640 bits.  The 1GbE interframe gap is allowed to be as
low as 64 bit times.  So, call that 640+64 or 704 bits.  That is a
maximum then of a little over 1.42 million queries per second (since
1GbE is full-duplex).  

Now, I have seen aggregate netperf TCP_RR tests achieve in excess of
1.8M transactions (queries) per second over a 10GbE NIC, but never to
a single-threaded process. The 10GbE NIC I was using at the time did
have a low-ish PPS limit.

The most I've seen a single netperf *single-byte* burst-mode test do
is on the order of 350K transactions per second, and that is when
netperf is bound to a core other than the one taking interrupts from
the NIC to get some additional parallelism.  In a netperf TCP_RR test,
netperf does virutally nothing but a send()/recv() pair and a couple
conditionals and adds.

Are there "multi-threaded" NTP server implementations?  If not, I
suspect it is possible for an NTP server to saturate before the 1GbE
network to which it is connected.

rick jones
oxymoron n, Hummer H2 with California Save Our Coasts and Oceans plates
these opinions are mine, all mine; HP might not want them anyway... :)
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

More information about the questions mailing list