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

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Message-ID: <m1my0thelq.fsf@fess.ebiederm.org>
Date:	Mon, 04 Jan 2010 11:09:05 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"H. Peter Anvin" <hpa@...or.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\@vger.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

"H. Peter Anvin" <hpa@...or.com> writes:

> On 01/04/2010 08:18 AM, Eric W. Biederman wrote:
>> Yinghai Lu <yinghai@...nel.org> writes:
>> 
>> This patch is wrong.
>> 
>>> between FIRST_EXTERNAL_VECTOR (0x20) and FIRST_DEVICE_VECTOR (0x41)
>>>
>>> for 0x20 and 0x2f, we are safe be used_vectors will prevent it to use used one.
>> 
>> We can not use any of 0x20 - 0x2f for ioapic irqs.  We need the entire
>> priority level to ensure that the irq move cleanup ipi is of a lower
>> priority.
>> 
>
> Almost makes one want to abuse 0x1f for that.  Although 0x00..0x1f are
> reserved for exceptions, the APICs range down to 0x10, and well, when
> 0x1f ends up actually getting used as an exception vector that we
> support, then we can trivially change that.  In the meantime it would
> actually make use of an otherwise-unusable APIC priority level.

An optimization like that (with a big fat comment) seems reasonable
to me.

Eric
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