Re: Re: [Rtlinuxgpl] Interrupt Prioritization

Victor Yodaiken <[email protected]> Tue, 3 Jan 2006 18:36:29 -0700
Newsgroups gmane.linux.real-time.rtlinux.general
Organization FSM Labs
Message-ID <[email protected]>
On Tue, Jan 03, 2006 at 05:48:35PM -0500, Calin A. Culianu wrote:
> OK.  I get it.  One last question.  "If B is running and C becomes 
> runnable... ".
> 
> That happens if the timer interrupt fires, right?
> 
> So that means that the timer interrupt is always on when rt tasks are 
> running?
> 
> Is that always ok?  I mean doesn't that sort of introduce lots of jitter?

Not on modern machines and the alternative is to let a scheduled high 
priority task wait on a lower priority task.

On older machines, Michael used a complex trick to reduce timer jitter by
only scheduling the timer to expire if a high priority task was waiting.

> 
> (I am sure I can research this myself.. but your help is appreciated!!)
> 

-- 
---------------------------------------------------------
Victor Yodaiken 
Finite State Machine Labs: The RTLinux Company.
www.fsmlabs.com  www.rtlinux.com
1+ 505 838 9109

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