linux-kernel - Re: [PATCH] X86: Change the default value of nr_irqs from 32 to NR

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Date:	Wed, 20 Aug 2008 00:19:57 +0100
From:	Alex Nixon <alex.nixon@...rix.com>
To:	Yinghai Lu <yhlu.kernel@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Jeremy Fitzhardinge <Jeremy.Fitzhardinge@...rix.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] X86: Change the default value of nr_irqs from 32 to NR_IRQs

Yinghai Lu wrote:
> when !CONFIG_HAVE_SPARSE_IRQ, with dyn_array, could allocate irq_desc
> and etc as less as possible.
> when CONFIG_HAVE_SPARESE_IRQ, no actually meaning for nr_irqs.
> 
> YH

So I believe the only case this affects is !CONFIG_HAVE_SPARSE_IRQ

The worry is that with CONFIG_HAVE_DYN_ARRAY we may waste memory by 
pre-allocating more irq_descs than may be necessary (NR_IRQs vs 32)?

With !CONFIG_HAVE_DYN_ARRAY however, a static array of size NR_IRQS is 
allocated instead - so doesn't defaulting nr_irqs back to NR_IRQS just 
revert to the old behaviour (with the exception of the irq_descs being 
allocated in pre_alloc_dyn_array instead)?

- Alex
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