Re: [chrony-users] Fwd: Chrony malfunctioning at beaglebones

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On Mon, Nov 16, 2015 at 8:09 AM, Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:
> The problem with abs64() and the one in the thread were both actually
> not related directly to the nohz code. The effect of disabling nohz in
> 3.17+ kernels should be pretty small anyway and even if the nohz
> option was broken it would probably not explain the difference in the
> PPS jitter you see when the CPU is forced to wakeup.
> Is the CPU on BBB entering some deep sleep states like C2 and C3?
> Maybe the idle=halt kernel option could reduce the observed jitter.

It was not entering cpuidle states, actually the beaglebone support
for that just appeared this week.

So I just tried to recompile a kernel and disabling dyntick. That's
it. The jitter dropped to the best values I had before when having a
task running every 1ms, so AFAIK nohz=off is really not working.

And yes, beside dyntick, now with the cpuidle states, I also have to
disable them. So thanks for the advise.

Not sure if I should collect any more data regarding the nohz problem,
on other platforms, before I refer this to the kernel people.


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