linux-kernel - Re: [PATCH 3/4] irq: initialize nr_irqs based on nr_cpu

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Date:	Sat, 10 Jan 2009 23:50:10 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Mike Travis <travis@....com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Yinghai Lu <yinghai@...nel.org>,
	Jack Steiner <steiner@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] irq: initialize nr_irqs based on nr_cpu_ids


* Mike Travis <travis@....com> wrote:

> Impact: Reduce memory usage.
> 
> This is the second half of the changes to make the irq_desc_ptrs be
> variable sized based on nr_cpu_ids.  The algorithm is the same as the
> setting of NR_IRQS except use nr_cpu_ids instead of NR_CPUS.  This is
> only when CONFIG_SPARSE_IRQS=y.
> 
> Signed-off-by: Mike Travis <travis@....com>
> ---
>  kernel/irq/handle.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> Files linux-2.6-for-ingo.orig/kernel/irq/.handle.c.swp and linux-2.6-for-ingo/kernel/irq/.handle.c.swp differ
> --- linux-2.6-for-ingo.orig/kernel/irq/handle.c
> +++ linux-2.6-for-ingo/kernel/irq/handle.c
> @@ -133,6 +133,11 @@ int __init early_irq_init(void)
>  	int legacy_count;
>  	int i;
>  
> +	/* initialize nr_irqs based on nr_cpu_ids */
> + 	nr_irqs =  (8 * nr_cpu_ids) > (32 * MAX_IO_APICS) ?
> + 			NR_VECTORS + (8 * nr_cpu_ids) :
> + 			NR_VECTORS + (32 * MAX_IO_APICS);
> +

this will break non-x86. Please move this to the x86 early-irq-init 
function instead, and also sync it up with the current NR_IRQS sizing 
macro.

I.e. do not duplicate the numbers but introduce some sort of 
max_nr_irqs(nr_cpus) define that is used to initialize NR_IRQS and also 
used later on to narrow down nr_irqs later on.

	Ingo
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