Re: [rtl] Q: when are linux interrupt handlers are invoked?

[yodaiken@chelm.cs.nmt.edu]

On Fri, May 08, 1998 at 04:36:51PM -0700, Jun Sun wrote:
> 
> The RTL white paper says :
> 
> 	In RT-Linux, all interrupts are initially handled by the Real-Time 
> 	kernel and are passed to the Linux task only when there are no 
> 	real-time tasks to run. 
> 
> However, the rt-linux code seems to suggest that interrupts are passed to
> Linux before real-time tasks get a chance to run. Here is the reasoning :
> 
> 1. I assume assembly symbol "linux_IRQxx_interrupt" is the lowest-level
>    interrupt handler for those interrupts that are not interested by
>    any real-tasks.
> 
> 2. "linux_IRQxx_interrupt" sets a irq flag in SFREQ and will invoke 
>    "S_IRET" if the soft interrupt is turned on in linux.
> 
> 3. "S_IRET" will call the the linux interrupt handler through "SFIDT" table.
> 
> I don't see anywhere RT tasks have a chance to execute before the linux 
> interrupt handler is invoked.  It seems like RT tasks can be delayed 
> by lengthy linux interrupt handlers.  
> Is this right? Can someone either confirm this or point out what is 
> wrong with the logic?

The hard interrupts  are re-enabled before the linux driver is called.


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