hi res timer

Jan 20, 2006 4 Replies
Z

=_NextPart_000_0006_01C61D9F.272A7FA0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable



Hi,



In linux 2.6 kernel the clock_getRes says that it is 1ms accuracy. =20



I basically want to have a method run every 1 ms. However when I run it = on linux 2.6 kernel fedora core 2 i don't get that and I get a lot of = jitter.



We have tried running it as root and used top to renice it to a high = level.



What are we doing wrong? =20 Can someone point me to an example chuck of code that shows a hi-res = timer at over 100 hz.



thanks in advance



Vote
Twitter Facebook LinkedIn
M

Linux is not a hard realtime system, so you will find a jitter of _any_ size if you wait long enough and produce enough stress in the system.

If you want reliable timing you need to add something like RTAI.

-Michael

Vote
Twitter Facebook LinkedIn
R

Which 2.6 kernel, there are several of them :) Is it saying "accuracy" or is it saying "precision?"

What do you get and what is your definition of "a lot" of jitter? What would be acceptable jitter for your situation?

I seem to recall that there can be three values for HZ now in a

2.6.mumble kernel (maybe that cam in .14?) 100, 250 and 1000 I wonder if running HZ at 1000 and perhaps playing with timeslices and such might get things going "well enough" without having to go all the way to what I think is RTAI?

rick jones

firebug n, the idiot who tosses a lit cigarette out his car window these opinions are mine, all mine; HP might not want them anyway... :) feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...
Vote
Twitter Facebook LinkedIn
I

I was playing with .14 recently and saw it there. I'm not sure if it came any earlier, though.

echo izn@pwlvkqrw.nwv|tr zwvq aeto
Vote
Twitter Facebook LinkedIn
M

If you don't mind that _sometimes_ the timing condition is not met, you are fine (2.6 is said to be a better _soft_realtime_ system than previous versions). But there is no guarantee.

-Michael

Vote
Twitter Facebook LinkedIn

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required