Re: better leve triggered IRQ management needed

[Alan Cox <alan@redhat.com>]

On Mon, Apr 24, 2006 at 02:07:01PM -0700, Linus Torvalds wrote:
> debugging standpoint. So even if it's just that every registered SA_SHIRQ 
> would get a heartbeat at least once every five seconds (and we'd limit it 
> to SA_SHIRQ exactly because a driver that doesn't have that set may get 
> confused if it gets extra interrupts), that might sound totally useless, 
> but it might actually help somebody who otherwise might just make a pretty
> useless "the machine hung" bug-report.

Have to watch enable/disable_irq and the other races here.

> The fake interrupt could even print out a warning if somebody returns 
> SA_HANDLED (since normally there _shouldn't_ have been any work to handle 
> for it), and if that means that for somebody, things go from "the machine 
> hung" to "the machine got very slow, and printed out 'fake interrupt for 
> ide0 returned SA_HANDLED!'", that would potentially be a big debug aid.

There are high rate IRQ sources that would trigger that erratically due to
races but it could be useful in some kind of "linux irqdebug" mode

> We've had our ass saved quite a few times now by the irq storm detector 
> ("irq X: nobody cared" and friends), which has helped debug irqs that 
> haven't been set up properly, that I'm convinced things like this might 
> well make a huge deal.

Yep

Alan
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