linux-kernel - Re: Question about interrupt routing and irq allocation

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Message-ID: <20080527145606.GB24457@elte.hu>
Date:	Tue, 27 May 2008 16:56:06 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Avi Kivity <avi@...ranet.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Keir Fraser <Keir.Fraser@...citrix.com>
Subject: Re: Question about interrupt routing and irq allocation


* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

>> So the most intelligent method would be to reserve the Linux irq 
>> itself but not the vector, i.e. allocate from irq_cfg[] in 
>> arch/x86/kernel/io_apic_64.c so that the irq number does not get 
>> reused - setting irq_cfg[irq].vector to -1 will achieve that.
>
> I'm initially targeting 32-bit, though obviously I'd like something 
> that works for both 32 and 64 bit.  irq_cfg[] is missing in 
> io_apic_32.c; would I achieve the same effect by setting 
> irq_vector[irq] = 0xff or something?

ok, here comes the next phase of a rather cunning plan: please unify 
these vector allocators first! ;-)

it's nontrivial but would result in rather nice code. I dont know 
whether we want to extend per-CPU vectors to 32-bit as well ... but 
might be worth an attempt and we could give any exploratory patches a 
try in -tip. Eric, what do you think about the general approach?

this would also pave the way towards unified APIC code. Hm?

	Ingo
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