linux-kernel - Re: [patch] x86, apic: use 0x20 for the IRQ_MOVE_CLEANUP

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Message-ID: <4B4BACCA.2040805@zytor.com>
Date:	Mon, 11 Jan 2010 14:57:14 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"ebiederm@...ssion.com" <ebiederm@...ssion.com>,
	Yinghai Lu <yinghai@...nel.org>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch] x86, apic: use 0x20 for the IRQ_MOVE_CLEANUP_VECTOR instead
 of 0x1f

On 01/11/2010 02:53 PM, Suresh Siddha wrote:
> 
>> However, my most serious concern with this patch is that there is a
>> fairly significant change due to this patch, which is that the legacy
>> IRQ vectors now fall *inside* the FIRST_DEVICE_VECTOR range.  This isn't
>> a bad thing -- in fact, it is fundamentally the right thing to do
>> especially once we consider platforms which *don't* have the legacy IRQs
>> -- but it makes me scared of unexpected behavior changes as a result.
>> If you feel confident that that is not the case, could you outline why
>> it shouldn't be a problem?
> 
> In irqinit.c, we statically pre-assign the per-cpu vector to irq
> mappings (vector_irq) for all the legacy IRQ vectors. Similarly irq_cfg
> is statically initialized for legacy IRQ's in io_apic.c. So we won't be
> able to use this space for anything else.
> 

What enforces that, though?  The used_vector bitmap?  In the past it was
enforced simply by being < FIRST_DEVICE_VECTOR.

	-hpa

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