Re: Missing some interrupts

On Mon, 2009-06-08 at 09:45 -0700, wael showair wrote:

wael showair wrote:

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You cannot really rely on getting the exact same number of edge
interrupts that were emitted. At least not unless you have a hard RT
system and can guarantee that you'll always dequeue them fast enough.

Yes, my system is a hard RT & i want to receive all the interrupts that
have been generated exactly

No. Linux is not hard RT. You cannot rely on this in a reliable way,
if for any reason the kernel masks interrupt for too long, which can
happen, you'll see that sort of coalescing happening.

what about using the RT-Preempt Patch? i can see that it will convert Linux
ti an RTOS.

Not only I don't think it's going to guarantee RT response (just improve
it), that's a pretty big hammer to work around what is a design bug in
your system in the first place :-)

i have check the function of do_IRQ: there is no ack called b 4 calling the
handler but actually it does the following:

You haven't read properly :-)

1. it gets the irq number using :
       irq = ppc_md.get_irq();

2. then it calls the handler : 
	if (irq != NO_IRQ && irq != NO_IRQ_IGNORE) {
			generic_handle_irq(irq);
	} else if (irq != NO_IRQ_IGNORE)
		/* That's not SMP safe ... but who cares ? */
		ppc_spurious_interrupts++;

i have checked the function of  generic_handle_irq  where it is defined
linux/irq.h & it calls the handler

No. It call the -flow- handler, which is a different thing (yes, the
terminology can be a bit confusing). The flow handler is configured
by the interrupt controller itself and will do whatever necessary
ack'ing, masking, EOI'ing etc... for a given PIC around the call to the
actual driver handler.

so from the previous code the processor or the pic does not ack but they
call my ISR handler.

They do. You missed it.

i have also read the specs of my OpenPIC & found that:

"the interrupt handler executing on the processor should then acknowledge
the interrupt by explicitly reading the IACK register.

Reading the IACK is what get_irq() does on OpenPIC.

The PIC unit
interprets this read as an interrupt acknowledge (IACK) cycle; in response,
the PIC unit returns the vector associated with the
interrupt source to the interrupt handler routine."

"At the end of the interrupt  the End Of Interrupt (EOI) register must be
set"

Which is done by the flow handler.

So the processor neither reads this iack register nor the handler set the
EOI register.

 
You obviously missed both :-)

Ben.