linux-kernel - Re: [PATCH] x86_64: resize NR_IRQS for large machines (re-submit)

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Date:	Wed, 26 Mar 2008 22:23:12 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Alan Mayer <ajm@....com>
Cc:	torvalds@...ux-foundation.org,
	linux-kernel list <linux-kernel@...r.kernel.org>,
	Robin Holt <holt@....com>, Jack Steiner <steiner@....com>,
	Russ Anderson <rja@....com>
Subject: Re: [PATCH] x86_64: resize NR_IRQS for large machines (re-submit)


* Alan Mayer <ajm@....com> wrote:

> On machines with very large numbers of cpus, tables that are 
> dimensioned by NR_IRQS get very large, especially the irq_desc table.  
> They are also very sparsely used.  When the cpu count is > 
> MAX_IO_APICS, use MAX_IO_APICS to set NR_IRQS, otherwise use NR_CPUS.

thanks Alan, applied this in place of the other patch.

this bit is still ugly:

> -#define NR_IRQS (NR_VECTORS + (32 *NR_CPUS))
> +#if NR_CPUS < MAX_IO_APICS
> +#define NR_IRQS (NR_VECTORS + (32 * NR_CPUS))
> +#else
> +#define NR_IRQS (NR_VECTORS + (32 * MAX_IO_APICS))
> +#endif
>  #define NR_IRQ_VECTORS NR_IRQS

but it doesnt really depart from the current status quo of huge 
[NR_IRQS] arrays either. Patches that make NR_IRQS a variable are 
welcome :)

	Ingo
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