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

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Date:	Mon, 11 Jan 2010 18:17:30 -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 01/11/2010 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...

> What guarantee we need is the interesting question.
> 
> The cleanup ipi is sent when we have seen an interrupt arrive at it's
> newly configured location.  It is possible that there is still an
> interrupt in flight to the old configured location (think NUMA where
> the interrupt has been migrated from off node to on node).  We want
> the guarantee that the ipi arrives after the inflight irq.  Which
> means on the wire ordering as well as in the local apic ordering is
> interesting.

I don't think there is any such guarantee possible, but that that has
nothing to do with the interrupt priority.  Suresh tells me that that is
handled by detecting and re-posting the migration IRQ.

> I am slammed with other stuff right now so I don't think I will have
> time to find the old documentation I was looking at for a couple of
> more days.

I'm wondering if what you're thinking of are the really old LAPICs which
could only remember two pending interrupts per priority level?

	-hpa

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

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