linux-kernel - Re: lockdep and threaded IRQs

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Message-Id: <20090302145757.38a44307.akpm@linux-foundation.org>
Date:	Mon, 2 Mar 2009 14:57:57 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>
Cc:	a.p.zijlstra@...llo.nl, dbrownell@...rs.sourceforge.net,
	tglx@...utronix.de, me@...ipebalbi.com,
	linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
	felipe.balbi@...ia.com, dmitry.torokhov@...il.com,
	sameo@...nedhand.com
Subject: Re: lockdep and threaded IRQs

On Mon, 02 Mar 2009 14:46:47 -0800 (PST)
David Miller <davem@...emloft.net> wrote:

> From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date: Mon, 02 Mar 2009 23:19:31 +0100
> 
> > I state that every !IRQF_DISABLED usage is a bug, either due to broken
> > hardware or broken drivers.
> 
> We'll send you the bill to have everyone's hardware
> replaced :-)

yes, but with what?

No matter how fast all our interrupt handlers are, running them with
local interrupts disabled has to worsen the worst-case interrupt
latency.

I don't see how removing !IRQF_DISABLED improves the kernel - in fact
there's a latency argument for making !IRQF_DISABLED the default.
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