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Date: Mon, 11 Jan 2010 14:57:14 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Suresh Siddha <suresh.b.siddha@intel.com>
CC: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
       "ebiederm@xmission.com" <ebiederm@xmission.com>,
       Yinghai Lu <yinghai@kernel.org>,
       "Maciej W. Rozycki" <macro@linux-mips.org>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: [patch] x86, apic: use 0x20 for the IRQ_MOVE_CLEANUP_VECTOR instead
 of 0x1f
References: <1263002989.2879.664.camel@sbs-t61.sc.intel.com>	 <4B47E7A9.6090904@zytor.com> <1263250418.2859.681.camel@sbs-t61.sc.intel.com>
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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