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From: Bruce Evans <bde@zeta.org.au>
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Subject: Re: New interrupt stuff breaks ASUS 2 CPU system
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On Fri, 7 Nov 2003, Stefan [iso-8859-1] E=DFer wrote:

> On 2003-11-07 20:04 +1100, Bruce Evans <bde@zeta.org.au> wrote:
> > However, using the apic almost doubles the overheads for the a45 cases.
> > This seems to be due to extra interrupts.  The UART and/or driver alrea=
dy
>
> Just another data point:
>
> Seems that the interrupt rate doubled for drm0 on my system
> (from 60 to 120 driving a LCD at 60Hz vertical refresh).
>
> I thought this might be a problem with shared interrupts (drm0
> and xl0 shared APIC IRQ 16), but removing the (actually unused)
> xl driver did not make a difference ...

Hmm.  My a45 UARTs are the only ones with a pci level triggered interrupt:

    Nov  7 01:48:44 gamplex kernel: ioapic0: Routing IRQ 5 -> intpin 19
    Nov  7 01:48:44 gamplex kernel: ioapic0: intpin 5 disabled
    Nov  7 01:48:44 gamplex kernel: ioapic0: intpin 19 trigger: level
    Nov  7 01:48:44 gamplex kernel: ioapic0: intpin 19 polarity: active-lo

There is only one other level triggered interrupt the system that is
used:

    Nov  7 01:48:44 gamplex kernel: ioapic0: Routing IRQ 11 -> intpin 18
    Nov  7 01:48:44 gamplex kernel: ioapic0: intpin 11 disabled
    Nov  7 01:48:44 gamplex kernel: ioapic0: intpin 18 trigger: level
    Nov  7 01:48:44 gamplex kernel: ioapic0: intpin 18 polarity: active-lo

and I suspect it may be doing strange things too: I found that rev.1.23
of ata_lowlevel.c broke atapicam, but the new interrupt code magically
fixed it.  One of the atapicam devices is the only device on IRQ11.

Bruce