[ntp:questions] Test ntpd performance

Kasper Pedersen spam at kasperkp.dk
Sun Sep 26 16:10:39 UTC 2010

On 09/26/2010 02:05 AM, R C wrote:
> Hi all,
> Thanks for your prompt response.
> My main intension of this scalability testing is to find out 
> 1. how long it takes for the ntpd server to serve 100,000 clients. 
> 2. What is the rate at which the server can process client requets.

A crude testing tool I once wrote:


Do NOT run this against a box you do not have permission
to test. This ntp client makes d-link&co look positively
angelic by comparison.

(2): An Atom N270 box handles 19k requests per second 
(2.4GHz Core2: 39k). That's ~50us per request. To test 
your box, you will need 3+ client machines, each running 
multiple instances of ntpload. Increase the number of 
instances until the box under test hits 100% cpu.

(1) is ambiguous. I assume the question is not about how
long the system takes to recover if you turn on 100.000
clients within a few hundred ms (the answer would be a
few seconds or less depending on buffer sizes), but 
rather CPU time. That's 50usec * 100k clients / 16 sec
= 31% of a 1.6GHz Atom core, if we assume that ALL your 
clients are awful. If they are merely rude, or all 
powered up within a minute, then expect 50usec * 100k 
clients / 64 seconds = 8% of a 1.6GHz Atom core.

You need to worry about the unasked question #3, which
is 'Do I accidentally have stateful firewalling in place,
and if so, does the router/firewall have memory for 
100k additional states?'. 

/Kasper Pedersen

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