Messages in this thread | | | Date | Sun, 12 Sep 2004 09:00:51 -0700 | From | "Martin J. Bligh" <> | Subject | Re: [PATCH 1/3] Separate IRQ-stacks from 4K-stacks option |
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--Zwane Mwaikambo <zwane@linuxpower.ca> wrote (on Sunday, September 12, 2004 11:45:19 -0400):
> yOn Sun, 12 Sep 2004, Martin J. Bligh wrote: > >> --Andrea Arcangeli <andrea@novell.com> 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. > > Currently we do use priorities on i386/APIC, albeit unintentionally by > assigning higher IRQs higher vectors resulting in a higher priority. > However interrupt priorities on non deterministic general purpose > operating systems seems pointless for the vast majority of the devices > plugged into boxes these days. Not to mention possible starvation issues > from high frequency long running interrupts.
Well, the idea is that long running interrupts get low prios ;-)
But yes, we're fairly non-deterministic, apart from the timer interrupt, etc which are at one end of the scale, though I forget which ;-)
M.
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