Re: [chrony-users] Time offset on versions 3+ without hw timestamping

Thanks, that seems like an interesting solution for power-saving. So far i disabled c-state and power management system-wide ( using /dev/cpu_dma_latency and governors) which gives really good results (more stable peer delay & std dev)

My PPS stddev get under 500ns, I however still get a constant offset betwen my PPS source and my ntp sources of about 8-9us (same with different PPS sources)

I really don't think it's a problem on the ntp servers side as it's using two asic-powered sources with hardware timestamping, get constant stddev under 10ns and can get value like 1.28us for "peer delay" and "max. error" under 4us when i bypass the switch (for testing purpose)

I guess there is still some delay somewhere on the PPS signal processing that gives this offset.

2017-10-06 9:40 GMT+02:00 Miroslav Lichvar <mlichvar@xxxxxxxxxx>:

On Mon, Sep 11, 2017 at 03:58:07PM +0200, Thibaut BEYLER wrote:
> Coming back to my isues with chrony 3 : I played a bit with cpu power
> management recently, at first to figure out first my problem with PPS
> sources, and found out that disabling the c-states would improve *drastically
> *chrony performances on my systems.

> Would there be any way to get those performance without disabling c-states
> system-wide ?

In case you are not following the chrony-dev list, there was a post
about a program that can disable power saving on a CPU core just for a
moment when it's waiting for the PPS interrupt.

https://listengine.tuxfamily.org/chrony.tuxfamily.org/chrony-dev/2017/10/msg00012.html

--
Miroslav Lichvar

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