Re: [linux-audio-user] IRQ conflicts, acpi, and linux audio

On Sun, 27 Nov 2005 13:12:46 -0800 Mark Knecht <markknecht(a)gmail.com> wrote: Actually sttictly speaking this isn't true. Any code will be preempted by an IRQ unless it is running with IRQ's off. The cool thing about -rt is now that every interrupt handler is split into top half and bottom half (if it before already was split like this, it is now split in 3 pieces). The top half basically just clears the IRQ line and sets up some stuff, so the kernel thread _bottom half_ irq handler is notified, there's something to do. The top half is extremely fast, so the time which might ever be spent in IRQ off situation is very short. So any IRQ interrupts user space for only a very very very short time. And everything else (working on the interrupt requests, etc) is now subject to scheduler decisions. The kernel threads which are the IRQ bottom half handlers can be prioritized with -rt. This gives the user the control to i.e. make the soundcard bottom half irq handler always have priority over the hd bottom half irq handler. And even jackd can have higher prio than the hd bottom half irq handler. To get this control (to prioritize one over the other) they each have to have their own kernel thread bottom half irq handler which doesn't work when they share an irq (though this might evenbe possible). Anyways, the XT-PIC/APIC priorities only count very little on a -rt system as the possible time windows in which each top half irq handler runs is very small, so collisions are unlikely.. It is important though to have individual irq's to be able to priritize on the level where it counts. Regards, Florian Schmidt -- Palimm Palimm! http://tapas.affenbande.org