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    SubjectRe: [patch] x86, apic: use 0x20 for the IRQ_MOVE_CLEANUP_VECTOR instead of 0x1f
    On 01/08/2010 06:09 PM, Suresh Siddha wrote:
    >
    > So change the IRQ_MOVE_CLEANUP_VECTOR to 0x20 and allow 0x21-0x2f to be used
    > for device interrupts. 0x30-0x3f will be used for ISA interrupts (these
    > also can be migrated in the context of IOAPIC and hence need to be at a higher
    > priority level than IRQ_MOVE_CLEANUP_VECTOR).
    >

    You're referring to when they're accessed as IOAPIC interrupts as
    opposed to ExtInt interrupts?

    >
    > -/*
    > - * First APIC vector available to drivers: (vectors 0x30-0xee). We
    > - * start allocating at 0x31 to spread out vectors evenly between
    > - * priority levels. (0x80 is the syscall vector)
    > - */
    > -#define FIRST_DEVICE_VECTOR (IRQ15_VECTOR + 1)
    > -#define VECTOR_OFFSET_START 1
    > -
    > #define NR_VECTORS 256
    >
    > #define FPU_IRQ 13
    > diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
    > index d5bfa29..5c090a1 100644
    > --- a/arch/x86/kernel/apic/io_apic.c
    > +++ b/arch/x86/kernel/apic/io_apic.c
    > @@ -1162,8 +1162,8 @@ __assign_irq_vector(int irq, struct irq_cfg *cfg, const struct cpumask *mask)
    > * Also, we've got to be careful not to trash gate
    > * 0x80, because int 0x80 is hm, kind of importantish. ;)
    > */
    > - static int current_vector = FIRST_DEVICE_VECTOR + VECTOR_OFFSET_START;
    > - static int current_offset = VECTOR_OFFSET_START % 8;
    > + static int current_vector = FIRST_DEVICE_VECTOR;
    > + static int current_offset = 0;
    > unsigned int old_vector;
    > int cpu, err;
    > cpumask_var_t tmp_mask;
    >

    I'm not entirely sure I like losing this bit, even though it isn't
    really necessary with your changes (VECTOR_OFFSET_START would be 0).
    I'm afraid we might end up with the same buglet being "reinvented" later.

    However, my most serious concern with this patch is that there is a
    fairly significant change due to this patch, which is that the legacy
    IRQ vectors now fall *inside* the FIRST_DEVICE_VECTOR range. This isn't
    a bad thing -- in fact, it is fundamentally the right thing to do
    especially once we consider platforms which *don't* have the legacy IRQs
    -- but it makes me scared of unexpected behavior changes as a result.
    If you feel confident that that is not the case, could you outline why
    it shouldn't be a problem?

    -hpa

    --
    H. Peter Anvin, Intel Open Source Technology Center
    I work for Intel. I don't speak on their behalf.



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