Duplicated hardware interrupts

[Peter Jeremy]

Whilst tracking down some interrupt latency problems, I've found that
I'm getting duplicate interrupts from some, but not all, devices.  The
double interrupts appear to always occur for some IRQs and never occur
on others.  Based on those symptoms, I wonder if there's a hardware
issue.

The system is a GigaByte GA-7VRX-P motherboard (VIA KT333) with an
Athlon XP-1800 running 5.3-RELEASE-p5 with APIC and ACPI:
CPU: AMD Athlon(tm) XP 1800+ (1533.40-MHz 686-class CPU)
  Origin = "AuthenticAMD"  Id = 0x662  Stepping = 2
  Features=0x383fbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,MMX,FXSR,SSE>
  AMD Features=0xc0480000<MP,AMIE,DSP,3DNow!>
real memory  = 536805376 (511 MB)
avail memory = 515629056 (491 MB)
ACPI APIC Table: <AMIINT AMIINI09>
ioapic0 <Version 0.2> irqs 0-23 on motherboard
...
acpi0: <AMIINT AMIINI09> on motherboard

I'm not seeing duplicate interrupts on atkbd0, rtc, fdc0, psm0 and ata0.

I am seeing duplicate interrupts on drm0, rl0 and my video capture card.

FWIW, the kernel code I'm using to check the interrupts is attached.
Userland just mmap's the buffer, converts it to ASCII and dumps it to
disk for later processing.

Has anyone else seen anything like this?
-- 
Peter Jeremy