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

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Message-ID: <20100325120021.GN20695@one.firstfloor.org>
Date:	Thu, 25 Mar 2010 13:00:21 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
	LKML <linux-kernel@...r.kernel.org>, jesse.brandeburg@...el.com,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] Prevent nested interrupts when the IRQ stack is near overflowing v2

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@...ux.intel.com -- Speaking for myself only.
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