Re: wiki page (was: Re: [linux-audio-user] dipping toes in 2.6 waters)

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Subject: Re: wiki page (was: Re: [linux-audio-user] dipping toes in 2.6 waters)
From: Florian Schmidt (mista.tapas_AT_gmx.net)
Date: Tue Aug 10 2004 - 23:33:56 EEST


On Mon, 09 Aug 2004 17:08:57 -0400
Lee Revell <rlrevell_AT_joe-job.com> wrote:

> I think Linux does not have ipls as such. When an interrupt handler
> is running it blocks further interrupts from the same source, but
> without the voluntary preempt patch, an interrupt from the disk will
> interrupt the soundcard interrupt handler. If you were to extend this
> scheme to support more than one priority (as opposed to 'this
> interrupt source' vs'other interrupt source'), you would have IPLs.

hi, i have to ask again, because there are still some unclarities for
me:

from links like this

http://roht.informatik.uni-halle.de/~ladischc/linux_interrupt_priorities.html

i get to the conclusion that there indeed was a hierarchy of IRQ's in
the traditional IRQ handlers in linux. I think this priority is located
in the PIC itself. I just don't know exactly how to understand the
implications. Does this priority only apply to irqs which happen to
happen on the exact same pci bus cycle? So, if soundcard and hd raise an
interrupt at the same time, the one with the higher PIC priority gets
precedence.. All this is still independent of the linux IRQ handlers. I
assume these PIC priorities still are effective when using threaded IRQ
handlers.

Now the question is: what happens in linux' traditional IRQ handler?
Does it honour PIC priorities? Let's assume an ide controller IRQ has
occured. Linux will handle it by running this irq's handler. This irq
handler disables further IRQ's from the same ide controller while it
runs. And reenable them when it finishes. Now during the running of the
irq handler a soundcard IRQ occurs. What happens? Does the PIC priority
have any influence on if the the Soundcards irq handler preempts the
ide-controller irq handler? Or does an irq from another source _always_
preempt irq handlers from other sources? In the case of threaded
handlers this is pretty clear. Only higher priority [not PIC priority
but task priority] irq handlers will preempt lower priority ones. But in
the case of traditional handlers?

Flo

-- 
Palimm Palimm!
http://affenbande.org/~tapas/


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