Re: high precision tracking: trying to understand sudden jumps

starlight@xxxxxxxxxxx wrote:

The clients are a rag-tag assembly of diverse systems including a Centos 4.5 Linux i686, Linux x86_64, Sun Ultra 10, Sun Ultra 80, IBM RS/6000 44p, Windows 2003 X64, and a Windows XP laptop.

How are you interpolating the 16ms ticks on the Windows system? How are you disabling power management on the lap top?


It generally is working well, with the systems tracking anywhere from +/- 100 microseconds to +/- 500 microseconds most of the time.

How are you measuring the difference from true time? In principle, if ntpd can measure it, it will correct it.


However once or twice a day, all the systems experience a random, uncorrelated time shift of from one to several milliseconds. Had an issue where a UPS voltage correction shift

In which direction is the slip? Backward only slips against true time (these might appear as forward slips if the real error is in the server) are typically due to lost clock interrupts. If that is the case it implies you are using a tick rate of other than 100Hz. Please note that the Linux kernel code is broken for clock frequencies other than 100Hz and the use of 1000Hz significantly increases the likelihood of a lost interrupt.

The normal source of lsot interrupts is disk drivers using programmed transfers.

and cheap power supply on the Windows X64 box appeared to be a
problem, but that was fixed by configuring the UPS to consider 110V nominal instead of 120V.

.

Relevant Pages

  • Re: Tick counting problem
    ... How do you establish that ticks are being missed: ... I read LCD -- it shows smaller numer at higher frequencies. ... The second thing is, when I change type of "licz" to int, ... but with a 16MHz device I would have thought it could service 10K interrupts per second. ...
    (comp.lang.c)
  • Re: Tick counting problem
    ... How do you establish that ticks are being missed: ... I read LCD -- it shows smaller numer at higher frequencies. ... The second thing is, when I change type of "licz" to int, ... interrupts per second. ...
    (comp.lang.c)
  • Re: 64bit ticks, was Re: Changing p_swtime and td_slptime to ticks
    ... | ticks is used a lot. ... Also the number of interrupts are hz * number of ... cores in which the number of cores is going up quickly. ...
    (freebsd-arch)