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Date: Fri, 08 Jan 2010 13:11:57 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Yinghai Lu <yinghai@kernel.org>
CC: "Eric W. Biederman" <ebiederm@xmission.com>, Ingo Molnar <mingo@elte.hu>,
       Thomas Gleixner <tglx@linutronix.de>,
       Andrew Morton <akpm@linux-foundation.org>,
       Jesse Brandeburg <jesse.brandeburg@intel.com>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5/5] x86: update nr_irqs according cpu num
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On 01/08/2010 12:06 PM, Yinghai Lu wrote:
>>>
>>> Ouch!  Unless I misread this code this will leave nr_irqs at
>>> NR_IRQS_LEGACY. aka 16.
>>>
>>> Let's do something stupid and simple.
>>> nr_irqs = nr_cpus_ids * 256;  /* Semi-arbitrary number */
>>
>> This would be 1048576 on the biggest machines we currently support.
>> Now, the number of IRQ *vectors* is limited to
>> (224-system vectors)*(cpu count), so one could argue that if there is
>> anything that is not semi-arbitrary it would be that number, but that
>> doesn't account for vector sharing.
> 
> (256 - 32 - 16 - system_vectors) * cpu_count + 16
> 
> the 16 is legacy from IRQ0 to 15 has domain with all cpus set.
> 

... assuming you're on a platform with a legacy PIC.  I would like to
see the legacy PIC hard-coded assumptions to go away, and instead be
done as runtime allocations on the relevant platforms.

> some interface in /proc/interrupts need it to make sure sth in sequence.

I can't even parse this sentence, never mind figuring out what it would
mean.  Certainly there is a better way to do that?

	-hpa