Re: Real-Time Preemption, -RT-2.6.12-final-V0.7.50-24

Daniel Walker
2005-07-12T14:28:45Z

On Tue, 2005-07-12 at 16:02 +0200, Ingo Molnar wrote:
> * Karsten Wiese <annabellesgarden@yahoo.de> wrote:
>
> > Hi Ingo
> >
> > I've refined io_apic.c a little more:
>
> great. I've applied these changes and have released the -28 patch. (note
> that the last chunk of your patch was malformed, have applied it by
> hand.)
>
> i'm wondering what your thoughts are about IOAPIC_POSTFLUSH - i had to
> turn it on unconditionally again, to get rid of spurious interrupts and
> outright interrupt storms (and resulting lockups) on some systems.
> IOAPIC_POSTFLUSH is now causing much of the IO-APIC related IRQ handling
> overhead.

I observed a situation on a dual xeon where IOAPIC_POSTFLUSH , if on,
would actually cause spurious interrupts. It was odd cause it's suppose
to stop them .. If there was a lot of interrupt traffic on one IRQ , it
would cause interrupt traffic on another IRQ. This would result in
"nobody cared" messages , and the storming IRQ line would get shutdown.

This would only happen in PREEMPT_RT .

Daniel