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

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Message-ID: <4B4E340F.7080106@zytor.com>
Date:	Wed, 13 Jan 2010 12:58:55 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Suresh Siddha <suresh.b.siddha@...el.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	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 01/13/2010 12:36 PM, Eric W. Biederman wrote:
> "H. Peter Anvin" <hpa@...or.com> writes:
> 
>> On 01/11/2010 05:52 PM, Eric W. Biederman wrote:
>>>
>>> After having the documentation quoted at me.  I am having a distinct
>>> memory of one piece of documentation saying:
>>> "interrupts within a priority level can be delivered in any order"
>>>
>>> So I am guessing there is not any ordering of interrupts in the same
>>> priority level until they get to the local apic.
>>>
>>
>> There is no ordering of interrupts before they hit the local APIC, since
>> the local APIC is what would serialize them...
> 
> The io apic serializes them, and sends them over either the 2-wire
> bus or the front side bus.   How much serialization and prioritization
> happens at that point I am not certain, but some certainly happens
> before you get to the local apic.
> 

Specifically, from the 82093AA spec:

"The interrupt number or the vector does not imply a particular priority
for being sent.  The IOAPIC continually polls the 24 interrupts in a
rotating fashion, one at a time.  The pending interrupt polled first is
the one sent."

In other words, the prioritization is all done at the LAPIC.

	-hpa

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