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

[Daniel Walker]

On Tue, 2005-07-12 at 16:02 +0200, Ingo Molnar wrote:
> * Karsten Wiese <annabellesgarden@xxxxxxxx> 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

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