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Re: [Xen-devel] NR_PIRQS vs. NR_IRQS

To: Jan Beulich <jbeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] NR_PIRQS vs. NR_IRQS
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Fri, 14 Nov 2008 08:00:37 +0000
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On 14/11/08 07:54, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx> wrote:

>>> I agree with keeping this naming distinction of course, although I think
>>> allowing NR_IRQS > NR_VECTORS right now is not very useful. But maybe you
>>> have a box in mind that needs it?
>> 
>> I had sent a mail a few days ago on this, where IBM was testing 96 CPU
>> support (4-node system), and it crashing because of a PIRQ ending up in
>> DYNIRQ space (kernel perspective), because there being 300+ IO-APIC
>> pins. While the crash ought to be fixed with the subsequent patch, it's
>> clear that none of the devices with an accumulated pin number greater
>> than 255 will actually work on that system.
> 
> Oh dear. :-D

Is fixing this actually any harder than just bumping NR_IRQS/NR_PIRQS in Xen
and NR_PIRQS in Linux? Have IRQS and VECTORS got somehow accidentally tied
together in Xen?

These parameters should probably be build-time configurable.

 -- Keir



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