linux-kernel - Re: [patch (take 2)] genirq: fix simple and fasteoi irq handlers

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Date:	Mon, 6 Aug 2007 09:19:32 +0200
From:	Jarek Poplawski <jarkao2@...pl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Gabriel C <nix.or.die@...glemail.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jean-Baptiste Vignaud <vignaud@...dmail.fr>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	shemminger <shemminger@...ux-foundation.org>,
	linux-net <linux-net@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, marcin.slusarz@...il.com
Subject: Re: [patch (take 2)] genirq: fix simple and fasteoi irq handlers

On Mon, Aug 06, 2007 at 08:14:59AM +0200, Ingo Molnar wrote:
> 
> * Jarek Poplawski <jarkao2@...pl> wrote:
> 
> > Subject: genirq: fix simple and fasteoi irq handlers
> > 
> > After the "genirq: do not mask interrupts by default" patch interrupts 
> > should be disabled not immediately upon request, but after they 
> > happen. But, handle_simple_irq() and handle_fasteoi_irq() can skip 
> > this once or more if an irq is just serviced (IRQ_INPROGRESS), 
> > possibly disrupting a driver's work.
> 
> nice fix. I think this is exactly the type of bug we were hoping to be 
> able to identify and fix, and it could explain the regression in its 
> entirety. The big question - does it fix Marcin's regression?

Alas, there still could be something more... To be more sure, even
with this, there should be some debug printk (which could mess too),
but I don't know how much patience (and similar boxes...) Marcin has.
Of course, this "temporary fix" in -rc2 should give us more time.
But, I think you should confirm this gain with levels (I mean there
could be some saving on flag setting/ checking too). E.g. I've thought
about adding another ioapic_chip struct for fasteoi without .retrigger
(and maybe with .disable = .mask) maybe with some #ifdef CONFIG_...,
but maybe there could be reconsidered IRQ_DELAYED_DISABLE too (but
with this, there probably was a possibility to run this hw ->retrigger
'by chance' too, so with some strange IO-APICS there would be still
an unnecessary risk here).

The big question for me is still why this isn't more common: it seems
some (most of?) IO-APICS have some safety against this?

BTW: Marcin, if you're still willing to test anything (and your box is
alive after my previous 'could not make any damage' patch - sorry!),
this should be done with something before -rc2, so 2.6.22 or .23-rc1.

Jarek P.

PS: I've just read Marcin's messages - so, happily, it seems
everybody's alive! Thanks.
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