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SubjectRe: Subject: [PATCH 1/2] x86: get back 15 vectors
From(Eric W. Biederman)
DateMon, 04 Jan 2010 11:09:05 -0800
"H. Peter Anvin" <hpa@zytor.com> writes:

> On 01/04/2010 08:18 AM, Eric W. Biederman wrote:
>> Yinghai Lu <yinghai@kernel.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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