linux-kernel - Re: [PATCH] irq: Start the transition of irq

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Date:	Sun, 21 Mar 2010 15:43:47 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
cc:	Yinghai Lu <yinghai@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Julia Lawall <julia@...u.dk>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-arch@...r.kernel.org
Subject: Re: [PATCH] irq: Start the transition of irq_chip methods taking a
 desc

Eric,

On Sun, 21 Mar 2010, Eric W. Biederman wrote:
> 
> With SPARSE_IRQ irq_to_desc becomes an unnecessary lookup operation on
> the fast path of dispatching irqs to their handlers.  We can avoid
> this cost by passing an irq_desc pointer instead of using an integer
> irq token to the irq_chip methods.
> 
> A single patch to convert all of the architectures is an unreviewable
> 2000+ line patch.  A gradual transition scenario with two sets of
> irq_chip methods in irq_chip is an unmanageable mess in kernel/irq.
> 
> So instead I define some macros so the generic irq code in kernel/irq/
> can compile either way based on a boolean Kconfig variable
> CONFIG_CHIP_PARAM_DESC.  This allows us to convert one architecture at
> a time, reducing the follow on patches to manageable proportions.  It
> is a little bit ugly but it is much better than the alternatives, and
> as soon as we finish the transition we can kill the macros.
> 
> I introduce the macros CHIP_ARG, CHIP_VAR, and CHIP_PARAM where
> appropriate.  I change a few declarations of irq as int to unsigned
> int.  I normalize the variables names in the functions that call
> chip methods to ensure that I have the variables irq and desc present
> allowing CHIP_ARG to work properly.  Most importantly none of the irq
> logic changes with this patch.

I like that approach very much. Is the output binary equivivalent?

Thanks,

	tglx
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