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

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Message-ID: <4B4BBEBA.4060403@zytor.com>
Date:	Mon, 11 Jan 2010 16:13:46 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
CC:	"Eric W. Biederman" <ebiederm@...ssion.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 04:06 PM, Suresh Siddha wrote:
>>
>> Yes, that's what I said.  My question was to Suresh what enforces that
>> in the case of his patch, which moves the legacy range into the middle
>> of the device vectors.
> 
> It's not the used_vector bitmap. That range will appear as used on all
> the cpu's and hence we won't be allocating it for anything else.
> 

OK, fair enough.

> Now the question is: for non-legacy (io-apic) case, instead of reserving
> this range for all the cpu's, does it make sense to generalize like any
> other vector?

It sounds like something that we could experiment with -- after
switching an IRQ to ioapic mode, make it a movable interrupt.  It
*seems* it should work, but it's scary stuff to muck with.

Eric, do you see any reason why it wouldn't work?  I truly couldn't
understand your previous remark, especially the bit about "it is
dangerous to play lowest priority irq games in that range".

	-hpa


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