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

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Date:	Fri, 08 Jan 2010 19:23:48 -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 01/08/2010 06:09 PM, Suresh Siddha wrote:
> From: Suresh Siddha <suresh.b.siddha@...el.com>
> Subject: x86, apic: use 0x20 for the IRQ_MOVE_CLEANUP_VECTOR instead of 0x1f
> 
> After talking to some more folks inside intel (Peter Anvin, Asit Mallick),
> the safest option (for future compatibility etc) seen was to use vector 0x20
> for IRQ_MOVE_CLEANUP_VECTOR instead of using vector 0x1f (which is documented as
> reserved vector in the Intel IA32 manuals).
> 
> Also we don't need to reserve the entire privilege level (all 16 vectors in
> the priority bucket that IRQ_MOVE_CLEANUP_VECTOR falls into), as the
> x86 architecture (section 10.9.3 in SDM Vol3a) specifies that with in the
> priority level, the higher the vector number the higher the priority.
> And hence we don't need to reserve the complete priority level 0x20-0x2f for
> the IRQ migration cleanup logic.
> 
> So change the IRQ_MOVE_CLEANUP_VECTOR to 0x20 and  allow 0x21-0x2f to be used
> for device interrupts. 0x30-0x3f will be used for ISA interrupts (these
> also can be migrated in the context of IOAPIC and hence need to be at a higher
> priority level than IRQ_MOVE_CLEANUP_VECTOR).
> 

I guess another thing is whether or not we can allocate 0x20 as a normal
vector if we don't need IRQ_MOVE_CLEANUP_VECTORS, and rely on the
used_vectors for that one as well.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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