linux-kernel - Re: [question] NR

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Date:	Wed, 24 Nov 2010 14:53:14 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Haojian Zhuang <haojian.zhuang@...il.com>
cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [question] NR_IRQS in genirq

On Wed, 24 Nov 2010, Haojian Zhuang wrote:
> On Wed, Nov 24, 2010 at 9:18 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > Why can nr_irqs become larger? Is that a theoretical problem or did
> > you run into this ?
> 
> My hardware environment is ARM. Each machine description can specify
> nr_irqs. In my implementation of PXA, NR_IRQS is fixed for SoC
> internal IRQs. And there's some additional board IRQs, we arrange them
> between NR_IRQS and nr_irqs. So nr_irqs will be larger than NR_IRQS if
> board IRQs exists.

And that's wrong. NR_IRQS is the upper bound. nr_irqs is the runtime
bound which is supposed to be <= NR_IRQS.

The whole point of sparse_irq is that it does not statically allocate
irq_desc[NR_IRQS] to reduce memory consumption if only a small number
of irqs are actuallt used by a specific board.

Thanks,

	tglx
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