[ntp:questions] Test ntpd performance

R C rc_work at yahoo.com
Sun Sep 26 16:44:05 UTC 2010

Hi Kasper,

thanks for your response. 

1. Can you please tell me how to use the tool ntpload.c.
2. Is there an executable to use it? 
3. What does it do exactly?

Thank you.


From: Kasper Pedersen <spam at kasperkp.dk>
To: questions at lists.ntp.org
Sent: Sun, September 26, 2010 9:10:39 AM
Subject: Re: [ntp:questions] Test ntpd performance

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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