Well, I found out that if i run a cpu stress test (i am using mprime
'torture test') while running chrony, suddenly my PPS source std dev goes
stable below 300ns.

So i guess this is realted to some kind of cpu scheduling. However i
disabled the c-state options in the bios, my CPU frequency is not altered
according to /proc/cpuinfo, and yet i still have bad results unless i run
this stress test.

Any idea ?


2017-09-01 15:52 GMT+02:00 Miroslav Lichvar <mlich...@redhat.com>:

> On Thu, Aug 31, 2017 at 05:25:09PM +0200, Thibaut BEYLER wrote:
> > No I tested it on ordinary x64 kernel (4.9 , 3.16 etc..) coming from
> debian
> > & fc repos with no custom options.
> >
> > I just installed pps-linux and invoked 'ldattach 18 /dev/ttyS0' (which
> also
> > loads pps_ldisc module) , maybe i'm missing something ?
>
> I'm not sure. Maybe the hardware cannot do better. From what I have
> seen, with a real serial port (no USB, etc) the PPS is usually stable to
> around
> 1 microsecond. For example, this is what I get with a Garmin 18x I have
> here:
>
> MS Name/IP address         Stratum Poll Reach LastRx Last sample
> ============================================================
> ===================
> #* PPS0                          0   4   377     8   +200ns[ +391ns] +/-
> 281ns
>
> Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std
> Dev
> ============================================================
> ==================
> PPS0                       11   6   161     +0.001      0.015    +18ns
>  415ns
>
> --
> Miroslav Lichvar
>
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