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SubjectRe: i8259 IRQ problems
On Thu, 23 Mar 2000, Manfred Spraul wrote:

> 1) why do we use 0x30 for the INVALIDATE_TLB_INTERRUPT?
> The interrupt is extremely time critical [another cpu waits for
> completion], and very short.
>
> Shouldn't we use an interrupt with the highest io apic priority?
> [0xF0..0xFF]?

AFAIR, APIC does not use the priority to choose the sequence of
dispensing interrupts. It dispenses them in the order they arrive.
Besides it doesn't really matter as about the only interrupt that can
arrive at the same time is the local timer interrupt -- LINT0 and LINT1
interrupts are not used this way, PC interrupts are currently not used at
all and if we receive an error interrupt then we probably have more
troubles than just the increased TLB invalidation latency. IIRC, there is
a fixed arbitration used between local and serial (i.e. these received
over the inter-APIC bus) interrupts but I don't remember the details -- I
can lookup docs if you are curious.

The priority is used to mask out some of interrupts when running higher
priority tasks. We do not use this model -- the task priority register is
set to zero once and forever.

--
+ Maciej W. Rozycki, Technical University of Gdansk, Poland +
+--------------------------------------------------------------+
+ e-mail: macro@ds2.pg.gda.pl, PGP key available +


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