Re: [Xenomai-help] Huge clock drift

[Pavel Machek <pma@domain.hid>]

On Sat 2011-05-28 16:32:45, Jan Kiszka wrote:
> On 2011-05-27 21:11, Gilles Chanteperdrix wrote:
> > On 05/27/2011 08:29 PM, Jonas Witt wrote:
> >> Sorry, I missed the NTP-part. I am not using NTP. Just plain timer 
> >> queries on a single system.
> >>
> >> My clock source is tsc which is the same for Xenomai I suppose.
> >>
> >> I wonder how a Xenomai task, even if it occupies 50% or even 90% of a 4 
> >> milliseconds time slice can interfere with the tsc. The tsc is not 
> >> incremented via an interrupt, is it? But I do not know much about the 
> >> inner workings of these functions.
> > 
> > The problem is not the clocksource, the problem is the timer interrupt.
> > The kernel expects 1 timer tick every millisecond.
> 
> Not on archs that are CONFIG_NO_HZ capable.

Umm. NO_HZ is only active while system is idle. Kernel will still
expect the periodic ticks when CPU is busy....

(I'm not sure how the compensation works; perhaps it can compensate
even while busy..)

									Pavel