Re: [PATCH 1/3] Separate IRQ-stacks from 4K-stacks option

[Martin J. Bligh]

--Andrea Arcangeli <andrea@xxxxxxxxxx> wrote (on Sunday, September 12, 2004 16:17:01 +0200):

> On Fri, Sep 10, 2004 at 05:34:21PM +0200, Arjan van de Ven wrote:
>> disabling is actually not a bad idea; hard irq handlers run for a very short
> 
> you mean hard irq handlers "should run" for a very short time. There can
> be slow hardware that needs a long time, and fast hardware that needs a
> short time, and in turn it makes perfect sense to allow nesting to give
> low latency to the "fast" onces, like it has always happened so far (not
> only in linux AFIK). Disabling nesting completely sounds a very bad
> idea to me, when "limiting nesting" can be achieved easily as confirmed
> by Alan too.

IIRC, what we did in PTX was have 16 SPL levels, each interrupt was assigned
a prio, and higher prio interrupts could interrupt lower prio ones (but not
the same prio or higher). There's some support for that in the APIC, I think,
something like the high nybble is prio, and the low nybble is just an index.

M.

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