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List:       systemd-devel
Subject:    Re: [systemd-devel] [PATCH 6/8] timesyncd: allow two missed replies before reselecting server
From:       Kay Sievers <kay () vrfy ! org>
Date:       2014-09-02 12:30:50
Message-ID: CAPXgP121zHYyHzUvxK13zyUt5KsW44q2NvgDFcFgfNa6bv82vA () mail ! gmail ! com
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On Tue, Sep 2, 2014 at 1:17 PM, Miroslav Lichvar <mlichvar@redhat.com> wrote:
> On Fri, Aug 29, 2014 at 06:31:10PM +0200, Kay Sievers wrote:
>> On Wed, Aug 27, 2014 at 4:47 PM, Miroslav Lichvar <mlichvar@redhat.com> wrote:
>> > After receiving a reply from the server, allow two missed replies before
>> > switching to another server to avoid unnecessary clock hopping when
>> > packets are getting lost in the network.
>>
>> Hmm, what's the reason to do this? The servers in the list are not
>> better or worse or sorted, are they?
>
> No, they are not, but offsets measured from different NTP servers are
> usually different (as the clocks are never exactly accurate, there are
> asymmetries in the network, etc.), so reselection introduces an offset
> that has to be corrected, possibly by stepping the clock. Also the
> polling interval may be shortened unnecessarily.
>
> Allowing few missed replies avoids reselection on every lost packet.

Sounds good. Applied.

Thanks,
Kay
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