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    SubjectRe: Subject: [PATCH 1/2] x86: get back 15 vectors
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    Yinghai Lu <yinghai@kernel.org> writes:

    > On 01/04/2010 11:09 AM, Eric W. Biederman wrote:
    >> "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.
    >
    > 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.

    Eric


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