Re: Real-Time Preemption, -RT-2.6.12-final-V0.7.50-24

[Ingo Molnar <mingo@elte.hu>]

* Karsten Wiese <annabellesgarden@yahoo.de> wrote:

> looked at -50-33 now and wonder why is mask_IO_APIC_irq() called twice 
> from __do_IRQ()? given a threaded interrupt: __do_IRQ() calls 
> desc->handler->ack(irq). ack points to 
> mask_and_ack_level_ioapic_irq(), which calls mask_IO_APIC_irq(irq).  
> some lines later in __do_IRQ() desc->handler->disable(irq) is called.  
> disable points to mask_IO_APIC_irq(), now being called a 2nd time. I 
> think this 2nd call isn't necessary. Is there a difference between 
> masking an interrupt line and disabling it? What am I missing?

you are not missing anything - but i found no easy way for the time 
being to get rid of the second masking.

> Back at 2.6.12-rc5-RT-48-16 mask_and_ack_level_ioapic_irq() also 
> contained the mask_IO_APIC_irq(irq) call and level interrupt-rates 
> where fine. Some versions later it vanished there. Why was that?

i reorganized how redirection is being done, and i've implemented 
auto-ACK for the i8259A, to reduce IRQ handling costs. One goal was to 
avoid the masking of the interrupt line for the timer interrupt on 
i8259A - but i think i'm going to revert that, it's causing too many 
problems all around.

	Ingo