Re: [PATCH][2.5][RFC] Using xAPIC apic address space on !Summit

From: James Cleverdon (
Date: Thu Dec 12 2002 - 22:32:06 EST

On Thursday 12 December 2002 07:26 pm, Zwane Mwaikambo wrote:
> On Thu, 12 Dec 2002, Nakajima, Jun wrote:
> > BTW, we are working on a xAPIC patch that supports more than 8 CPUs in a
> > generic fashion (don't use hardcode OEM checking). We already tested it
> > on two OEM systems with 16 CPUs.
> > - It uses clustered mode. We don't want to use physical mode because it
> > does not support lowest priority delivery mode.
> Wouldn't that only be for all including self? Or is the documentation
> incorrect?
> Thanks,
> Zwane

I'm not sure I understand your question. Lowest Priority delivery mode only
works with logical interrupts. (I've tried it with physical intrs. It fails
miserably.) The "all including self" and "all excluding self" destination
shorthands don't do lowest priority arbitration. They always deliver the
interrupt to the CPUs mentioned in the shortand.

Lowest priority delivery mode isn't _too_ useful in Linux yet. It would be
nice to preferentially target idle CPUs with interrupts in real time. That
means changing each CPU's Task Priority Register (TPR) to represent how busy
it is. I've got some patches to do that, but haven't posted them as anything
more than a RFC.

James Cleverdon
IBM xSeries Linux Solutions
{jamesclv(Unix, preferred), cleverdj(Notes)} at us dot ibm dot com

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