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SubjectRe: [patch] x86, apic: use 0x20 for the IRQ_MOVE_CLEANUP_VECTOR instead of 0x1f
On 01/11/2010 04:28 PM, Eric W. Biederman wrote:
> Sorry. I suck at multitasking.
> Without changes assign_irq_vector will reuse vectors in the range
> IRQ0_VECTOR to IRQ15_VECTOR in the code as it we currently ship it,
> when we switch irq0-15 into ioapic mode.
> Switching the loop to cover IRQ0_VECTOR to IRQ15_VECTOR is not a
> problem. I don't think it will find anything free as we assign those
> vectors on all cpus, but the data structures are fine.
> I am uncomfortable with the suggestion of sharing the priority of the
> IRQ_MOVE_CLEANUP_VECTOR with other interrupts. I know if it had be
> clear from the documentation that it was safe to share the irq level
> with other interrupts I would not have reserved the entire interrupt
> level for the IRQ_MOVE_CLEANUP_VECTOR.

What are the properties that you're looking for, and in what
documentation? We reviewed the Software Development Manual here at
Intel, and it rather explicitly states:

"Each interrupt priority level (sometimes interpreted by software as an
interrupt priority class) encompasses 16 vectors. Prioritizing
interrupts within a priority level is determined by the vector number.
The higher the vector number, the higher the priority within that
priority level. In determining the priority of a vector and ranking
of vectors within a priority group, the vector number is often divided
into two parts, with the high 4 bits of the vector indicating its
priority and the low 4 bit indicating its ranking within the priority

[Intel® 64 and IA-32 Architectures Software Developer’s Manual
Volume 3A: System Programming Guide, Part 1; September 2009, Order
Number 253668-032US; section 10.9.3, page 10-57f.]

So 0x20 is the lowest-priority vector within priority group 0x2.

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