linux-kernel - Re: [PATCH] sparse_irq aka dyn

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Message-ID: <491CB500.8090203@sgi.com>
Date:	Thu, 13 Nov 2008 15:15:12 -0800
From:	Mike Travis <travis@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Yinghai Lu <yinghai@...nel.org>, mingo@...e.hu, tglx@...utronix.de,
	hpa@...or.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sparse_irq aka dyn_irq v13

Andrew Morton wrote:
> On Thu, 13 Nov 2008 14:41:36 -0800
> Yinghai Lu <yinghai@...nel.org> wrote:
> 
>> Andrew Morton wrote:
>>
>>>> ...
>>>>
>>>>>> +static unsigned int kstat_irqs_legacy[NR_IRQS_LEGACY][NR_CPUS];
>>>>> Do these need to be 32-bit?  Maybe they'll fit in 16-bit, dunno.
>>>>>
>>>> struct irq_desc {
>>>>         unsigned int            irq;
>>>> #ifdef CONFIG_SPARSE_IRQ
>>>>         struct list_head        list;
>>>>         struct list_head        hash_entry;
>>>>         struct timer_rand_state *timer_rand_state;
>>>>         unsigned int            *kstat_irqs;
>>> That doesn't address my question.
>>>
>>> The above array can be very large.  Can we halve its size by using
>>> 16-bit quantities?  Will this code ever encounter IRQ numbers larger
>>> than 65536?
>>>
>> NR_CPUS=4096, NR_IRQS_LEGACY=16, and that array will be 256k bytes
>>
>> later could change that alloc_bootmem, so NR_CPUS will be replaced to nr_cpu_ids
> 
> Do the entries in that array need to be 32-bit?

That's a good question.  If there are 4k or 16k cpus, would the number of
irq's being "kstat'd" need to be > 64k?  (I'm not exactly sure why there
are NR_CPUS * NR_IRQS_LEGACY kstat entries per IRQ?)
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