linux-kernel - Re: [PATCH] X86: Change the default value of nr_irqs from 32 to NR

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Date:	Tue, 19 Aug 2008 12:00:43 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Alex Nixon" <alex.nixon@...rix.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Jeremy Fitzhardinge" <Jeremy.Fitzhardinge@...rix.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] X86: Change the default value of nr_irqs from 32 to NR_IRQs

On Tue, Aug 19, 2008 at 11:32 AM, Alex Nixon <alex.nixon@...rix.com> wrote:
> Yinghai Lu wrote:
>>
>> On Tue, Aug 19, 2008 at 11:13 AM, Alex Nixon (Intern)
>> <Alex.Nixon@...rix.com> wrote:
>>>
>>> Yinghai Lu <yhlu.kernel@...il.com> wrote:
>>>>
>>>> On Tue, Aug 19, 2008 at 9:55 AM, Alex Nixon <alex.nixon@...rix.com>
>>>> wrote:
>>>>>
>>>>> If the number of discovered IRQs is suspiciously low, this patch causes
>>>>> the number reported to default to NR_IRQS, rather than 32.  NR_IRQS has
>>>>> already been defined to be a >sensible value for the current system (in
>>>>> particular, at least 224 when paravirtualisation is involved).
>>>>>
>>>> if only one ioapic, nr will be 24<<1, you will get 48. Does pv has io
>>>> apic
>>>> ?
>>>>
>>>> YH
>>>>
>>> I'm not sure about the general case, but Xen does not (Jeremy correct me
>>> if
>>> I'm wrong).
>>>
>>> Unless I'm missing something (which I may well be; I'm new to this area
>>> of
>>> code), it seems more logical anyway to default back to the calculated
>>> system-specific value (NR_IRQS), instead of 32, which seems rather
>>> arbitrary.
>>
>> can you try !CONFIG_HAVE_SPARSE_IRQ and CONFIG_HAVE_SPARSE_IRQ ?
>>
>> YH
>
> Sorry I should have mentioned originally - the bug occurs both with
> CONFIG_HAVE_SPARSE_IRQ enabled, and disabled.

maybe we need special probe_nr_irqs for PV or not call that in
setup_arch for xen -- it will leave nr_irqs == NR_IRQS

YH
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