[time-nuts] Simple NTP server based on a Raspberry Pi

Shaun Kelly shaun at impsec.net
Mon Oct 29 20:34:36 EDT 2012


On 10/29/12 19:17 , Sarah White wrote:
> On 10/29/2012 7:53 PM, Chris Albertson wrote:
>> I'm curious what load average numbers do you get if you type "uptime"
>> after running NTP for some hours.
[snips]
>> Basically, I'm thinking this method (raspi + refclock) is a good way to
>> feed a handfull of public stratum 2 servers which by definition don't
>> have their own local refclock.
>>
>> If you made your raspi stratum 1 server publicly available via
>> pool.ntp.org it would almost certainly be overloaded.

I have a Raspberry Pi in the pool now (ntp.impsec.net), though I've set
bandwidth low (512k) so I am not seeing a great deal of load:

root at ntp2:/home/pi# uptime
  19:19:57 up 9 days, 21:54,  1 user,  load average: 0.03, 0.08, 0.15


top - 19:20:10 up 9 days, 21:54,  1 user,  load average: 0.03, 0.08, 0.15
Tasks:  55 total,   1 running,  54 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.3 us,  0.2 sy,  0.0 ni, 93.9 id,  5.4 wa,  0.0 hi, 0.2 si,  
0.0 st
KiB Mem:    220652 total,   205332 used,    15320 free,    35256 buffers
KiB Swap:   102396 total,      880 used,   101516 free,   145376 cached

Watching with tcpdump I am seeing only a few packets per second average,
withg some periods of burstiness where I see maybe 30 packets per second
where it will maybe get up to 10-15% busy.

[more snips]
>>
>> Let's assume a raspi can handle 200 packets per second without loosing
>> performance too badly (limited by cpu load, etc.)
I'd think that's probably close based on what I'm seeing, though again I'm
just eyeballing tcpdump.  Mind you, I'm not using the supported turbo modes
so there might be some wiggle room with mild overclocking.


-Shaun
(sig pending)



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