Re: [PATCH] Prevent nested interrupts when the IRQ stack is near overflowing v2

Andi Kleen
2010-03-25T12:00:23Z

On Thu, Mar 25, 2010 at 12:16:17PM +0100, Thomas Gleixner wrote:
> > Pretty much the only 'core' driver today which enables IRQs in the irq
> > handlers and needs it is the old IDE layer. There are also a couple of
> > drivers which play games with disable/enable_irq in the IRQ paths for
> > other reasons (lack of irq threads when written and a hardware model thats
> > totally SMP unfriendly). 8390 is the obvious one here and it at least
> > would be far far saner using threaded IRQs and normal locking with IRQs
> > unmasked.
>
> Right, but that's not the problem here. We talk about a (hopefully)
> well written interrupt handler which runs for a very short
> time.

The NIC handlers can do quite some work under high traffic.
Even with interrupt mitigation and NAPI.

> What's the point of running it with interrupts enabled ?

Other interrupts.

> Nothing, we just run into stack overflow problems. So what's better:
> an unreliable and ugly hackaround

I don't think that's a accurate description of the patch at all.
Besides I believe it's reliable in all cases that matter.

-Andi
--
ak@linux.intel.com -- Speaking for myself only.