[PATCH 0/5] Fix ntpd to not poll frequently

[Miroslav Lichvar]

On Wed, Oct 01, 2014 at 12:50:25AM +0200, Denys Vlasenko wrote:
> On Tue, Sep 30, 2014 at 11:44 AM, Miroslav Lichvar <mlichvar at redhat.com> wrote:
> > I'm not sure, I think it would be safer to follow the rule that if you
> > don't get a reply, you shouldn't ask again sooner than you would
> > otherwise.
> 
> Even if the poll interval is huge (may hours)?

What if most clients of the server were using this huge interval before the
server was unreachable and the traffic was already close to the maximum the
server was able to handle? Unlikely with public servers, but maybe some vendors
use only busybox and they have their own server.

FWIW, this is from the RFC 5905 (NTPv4):

   The poll() routine includes a feature that backs off the poll
   interval if the server becomes unreachable.  If reach is nonzero, the
   server is reachable and unreach is set to zero; otherwise, unreach is
   incremented by one for each poll to the maximum UNREACH.  Thereafter
   for each poll hpoll is increased by one, which doubles the poll
   interval up to the maximum MAXPOLL determined by the poll_update()
   routine.  When the server again becomes reachable, unreach is set to
   zero, hpoll is reset to the tc system variable, and operation resumes
   normally.

> > At this point I'm mostly concerned with the problem that nothing
> > increases the interval from the minimum (32 seconds) when the server
> > is unreachable. What are your thoughts on that?
> 
> Can you send me a patch which fixes this?
> More precisely, let's make ntpd increase poll interval modestly
> in this case (say, up to BIGPOLL).

Ok, I'll see if I can make one.

-- 
Miroslav Lichvar