linux-kernel - Re: [patch 4/4] genirq: add support for threaded interrupt handlers

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Message-Id: <20090226214514.f8a58731.akpm@linux-foundation.org>
Date:	Thu, 26 Feb 2009 21:45:14 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, peterz@...radead.org, rostedt@...dmis.org,
	jonathan@...masters.org
Subject: Re: [patch 4/4] genirq: add support for threaded interrupt handlers

On Thu, 26 Feb 2009 21:27:52 -0800 Arjan van de Ven <arjan@...radead.org> wrote:

> > 
> > Bearing in mind that the driver might choose to split the IRQ handling
> > between hard-irq context fastpath and process-context slowpath (I
> > hope), and that each path might want to take the same lock.
> > 
> 
> 
> Realistically, for the "we go threaded interrupts" case (which is
> opt-in), I think the only sane option is
> * the quickhandler runs with irqs off
> * the "slow" threaded handler runs with irqs on
> And we guarantee both of these conditions from the core, to the point
> that I think we should not allow any other combination.
> 
> This also should be fine for basically all cases; the quick handler
> really needs to be quick so irq off makes sense, and the slow handler
> can, worst case, turn off interrupts by itself, but normally is
> preemptable etc etc.

I was actually kinda surprised by the patch - it needs moderate changes
to each driver.  I'd have thought that it would be possible to arrange for
_all_ drivers to have their interrupt handlers automagically called from
process context with no driver changes.

Did anyone ever try that?  I think they did...
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