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To: Yinghai Lu <yinghai@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
       "H. Peter Anvin" <hpa@zytor.com>,
       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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	<m1bph4o1il.fsf@fess.ebiederm.org>
	<86802c441001081149k1be26027m62752604dca53aa@mail.gmail.com>
From: ebiederm@xmission.com (Eric W. Biederman)
Date: Fri, 08 Jan 2010 12:20:52 -0800
In-Reply-To: <86802c441001081149k1be26027m62752604dca53aa@mail.gmail.com> (Yinghai Lu's message of "Fri\, 8 Jan 2010 11\:49\:36 -0800")
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Yinghai Lu <yinghai@kernel.org> writes:

> On Fri, Jan 8, 2010 at 11:11 AM, Eric W. Biederman
> <ebiederm@xmission.com> wrote:
>> Yinghai Lu <yinghai@kernel.org> writes:
>>
>>> that is max number on run time.
>>
>> Ouch!  Unless I misread this code this will leave nr_irqs at
>> NR_IRQS_LEGACY. aka 16.
>
> nr_irqs is set to NR_IRQS before.

Yep my mistake.

>> Let's do something stupid and simple.
>> nr_irqs = nr_cpus_ids * 256;  /* Semi-arbitrary number */
>>
>> Ideally we would set "nr_irqs = 0x7fffffff;" but we have just enough
>> places using nr_irqs that I think those loops would get painful if we
>> were to do that.
>
> or you need have NR_IRQS = NR_CPUS * 256 at first,
>
> and then make nr_irqs = nr_cpu_ids * 224 ?

The important part is that NR_IRQS become an arbitrary number larger
than we can strictly support.

Based on my quick look the bad offenders (aka static sized arrays of
NR_IRQS) all look at NR_IRQS not nr_irqs.  So I don't see a point
in having nr_irqs < NR_IRQS.

So let's just kill arch_probe_nr_irqs() on x86.

Then we can worry about things like fixing xen and the interrupt
remapping code to not having NR_IRQS sized arrays.

Eric