linux-kernel - Re: Subject: [PATCH 1/2] x86: get back 15 vectors

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Message-ID: <4B423E24.90106@zytor.com>
Date:	Mon, 04 Jan 2010 11:14:44 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Yinghai Lu <yinghai@...nel.org>,
	Jesse Brandeburg <jesse.brandeburg@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	NetDEV list <netdev@...r.kernel.org>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>
Subject: Re: Subject: [PATCH 1/2] x86: get back 15 vectors

On 01/04/2010 11:04 AM, Eric W. Biederman wrote:
>>
>> any reason that we can not use 0x40?
> 
> Not that I now of.  Reading the comment it looks like it was only
> skipped so that the initial assignment of vectors would be.
> 
> 0x31, 0x41, 0x51, 0x61, 0x71, 0x81, 0x91, 0xa1, 0xb1, 0xc1, 0xd1, 0xe1
> Instead of.
> 0x30, 0x40, 0x50, 0x60, 0x70, 0x90, 0xa0, 0xb0, 0xc0, 0xc0, 0xe0
> 
> Which doesn't seem to be the worst notion, but at the point we are looking
> for every vector we can get it does seem to be problematic.
> 

This can presumably be worked around by tweaking the initial assignment
algorithm slightly, without losing a whole vector to that.

Also, if we abuse vector 0x1f as the IRQ reassignment vector, we free up
a full 16 vectors per CPU -- this seems worthwhile especially since it
is a decision that can be trivially undone in the future: this is all
kernel internal, we're not creating any kind of API.

	-hpa
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