One issue with lowest priority delivery mode (as well as Ingo's) is that it
could have negative impacts on L2 caches (actually we saw such instances).
So we also have a patch to balance interrupts load (using statistic data)
without moving them around frequently (mostly static) and I think we can
combine that patch and lowest priority delivery mode.
Jun
> -----Original Message-----
> From: James Cleverdon [mailto:jamesclv@us.ibm.com]
> Sent: Thursday, December 12, 2002 7:32 PM
> To: Zwane Mwaikambo; Nakajima, Jun
> Cc: Martin Bligh; John Stultz; Linux Kernel
> Subject: Re: [PATCH][2.5][RFC] Using xAPIC apic address space on !Summit
>
> 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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