Distribution:  Debian Woody
Hardware Environment:  

Motherboard is an ASUS P4C800-E with the 875P/ICH5-R chipset. I have the BIOS
configured into "enhanced" mode. The CD drive is a "Sony DVD RW DW-U10A"
(actually a DVD[+-]RW drive).  Also attached are a WDC WD360GD-00FNA0 SATA drive
and a 120G IDE drive.  The CPU is a 2.8 GHz P4 with HT enabled.

Software Environment:

* SMP kernel
* NOT using sata/scsi driver
* ide-scsi driver

Problem Description:

On the 2.4.24 kernel I'm seeing extremely high interrupt/system loads (on the
order of 15,000 interrupts/sec) on irq 11 when I load the ide-scsi module.
Mounting a filesystem on my CD drive (the only ide-scsi device) causes the
interrupts to go back to a normal level. Removing the ide-scsi module doesn't
cause the problem to clear up (the high level of interrupts continue). The
interrupt level is high enough to cause the system to lock up entirely sometimes
until some other interrupt (eg, from my USB mouse) is received.
Until I load ide-scsi, things work fine.

Twiddling unmaskirq in /proc/ide/hdc/settings does not help. Enabling debugging
in ide-scsi.c doesn't yield anything.  

Interestingly, this seems to clear the problem:

   echo "using_dma:1" > /proc/ide/hdc/settings

until the cdrom drive is accessed again.

% cat /proc/interrupts 
           CPU0       CPU1       
  0:    3813077          0    IO-APIC-edge  timer
  1:      15312          0    IO-APIC-edge  keyboard
  2:          0          0          XT-PIC  cascade
  5:     260633          0   IO-APIC-level  EMU10K1, ehci_hcd
 10:   13210839          0   IO-APIC-level  usb-uhci, usb-uhci, nvidia
 11:   77639978       1957   IO-APIC-level  ide0, ide1, ide2, usb-uhci, eth0
 14:          0          0   IO-APIC-level  Intel ICH5
 15:      91289          0   IO-APIC-level  usb-uhci
NMI:          0          0 
LOC:    3816101    3816101 
ERR:          0
MIS:       3060