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SubjectRe: Subject: [PATCH 1/2] x86: get back 15 vectors
Yinghai Lu <> writes:

> On 01/04/2010 11:09 AM, Eric W. Biederman wrote:
>> "H. Peter Anvin" <> writes:
>>> On 01/04/2010 08:18 AM, Eric W. Biederman wrote:
>>>> Yinghai Lu <> 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.
> so we can use [0x10, 0x1f]
> sth like this?

Something. We can not use all of 0x10 - 0x1f, it is simply
that hardware can address all of that. 0x10 is already defined
as something I forget what. 0x12 is already the MCE_VECTOR.

Since hardware has not yet defined 0x1f (and is not likely to for
a while. We can use that). So we wind up using hardware priority
a single ipi, and hardware exceptions.


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