if_sis interrupt storm

I'm seeing an interrupt storm on the sis0 interface on 7.0-CURRENT (both 
on the May snapshot and a build from today's sources) - when 
transferring data the interrupt rate increases until throttling on irq19 
occurs and the system hangs - I see lots of messages reporting the 
throttling of interrupts on irq19 but also get an ATA command timeout 
message.   The problem first occurred when backing up data over the LAN, 
but I also see the issue at lower data rates: at 200KB/s the interrupt 
rate increases about once every second.

vmstat -i:
interrupt              total        rate
irq1: atkbd0         777           3 
irq6: fdc0                 9           0
irq14: ata0         1377           5
irq15 ata1            664           2
irq19: sis0++    72515       308
cpu0: timer     469669      1998
Total              545011      2319


I've tried disabling ACPI and compiling a custom kernel without USB 
support (previously sis0 was sharing an interrupt with uhci0) but the 
problem still occurs.

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FreeBSD 7.0-CURRENT #1: Tue May 15 23:09:10 BST 2007
    brucec_at_neutrino.draftnet:/usr/obj/usr/src/sys/MYKERNEL
WARNING: WITNESS option enabled, expect reduced performance.
Timecounter "i8254" frequency 1193182 Hz quality 0
CPU: AMD Athlon(TM) XP 2800+ (1668.71-MHz 686-class CPU)
  Origin = "AuthenticAMD"  Id = 0x6a0  Stepping = 0
  
Features=0x383fbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,MMX,FXSR,SSE>
  AMD Features=0xc0400800<SYSCALL,MMX+,3DNow!+,3DNow!>
real memory  = 1073725440 (1023 MB)
avail memory = 1041543168 (993 MB)
ACPI APIC Table: <ASUS   A7V333  >
ioapic0: Changing APIC ID to 2
ioapic0 <Version 0.2> irqs 0-23 on motherboard
kbd1 at kbdmux0
ath_hal: 0.9.20.3 (AR5210, AR5211, AR5212, RF5111, RF5112, RF2413, RF5413)
acpi0: <ASUS A7V333> on motherboard
acpi0: [ITHREAD]
acpi0: Power Button (fixed)
acpi0: reservation of 0, a0000 (3) failed
acpi0: reservation of 100000, 3ff00000 (3) failed
Timecounter "ACPI-fast" frequency 3579545 Hz quality 1000
acpi_timer0: <32-bit timer at 3.579545MHz> port 0xe408-0xe40b on acpi0
cpu0: <ACPI CPU> on acpi0
acpi_button0: <Power Button> on acpi0
pcib0: <ACPI Host-PCI bridge> port 0xcf8-0xcff on acpi0
pci0: <ACPI PCI bus> on pcib0
agp0: <VIA 8367 (KT266/KY266x/KT333) host to PCI bridge> on hostb0
pcib1: <ACPI PCI-PCI bridge> at device 1.0 on pci0
pci1: <ACPI PCI bus> on pcib1
vgapci0: <VGA-compatible display> mem 
0xde000000-0xdeffffff,0xe0000000-0xefffffff,0xdd000000-0xddffffff irq 16 
at device 0.0 on pci1
atapci0: <Promise PDC20276 UDMA133 controller> port 
0xd800-0xd807,0xd400-0xd403,0xd000-0xd007,0xb800-0xb803,0xb400-0xb40f 
mem 0xdc800000-0xdc803fff irq 19 at device 6.0 on pci0
atapci0: [ITHREAD]
ata2: <ATA channel 0> on atapci0
ata2: [ITHREAD]
ata3: <ATA channel 1> on atapci0
ata3: [ITHREAD]
pci0: <serial bus, FireWire> at device 7.0 (no driver attached)
pci0: <serial bus, USB> at device 9.0 (no driver attached)
pci0: <serial bus, USB> at device 9.1 (no driver attached)
pci0: <serial bus, USB> at device 9.2 (no driver attached)
sis0: <NatSemi DP8381[56] 10/100BaseTX> port 0xa400-0xa4ff mem 
0xda800000-0xda800fff irq 19 at device 12.0 on pci0
sis0: Silicon Revision: DP83815D
miibus0: <MII bus> on sis0
ukphy0: <Generic IEEE 802.3u media interface> PHY 0 on miibus0
ukphy0:  10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, auto
sis0: Ethernet address: 00:40:f4:57:98:71
sis0: [ITHREAD]
pci0: <serial bus, FireWire> at device 13.0 (no driver attached)
pci0: <multimedia, audio> at device 14.0 (no driver attached)
pci0: <input device> at device 14.1 (no driver attached)
atapci1: <AcerLabs M5281 SATA150 controller> port 
0x9400-0x9407,0x9000-0x9003,0x8800-0x8807,0x8400-0x8403,0x8000-0x800f 
irq 19 at device 16.0 on pci0
atapci1: [ITHREAD]
ata4: <ATA channel 0> on atapci1
ata4: [ITHREAD]
ata5: <ATA channel 1> on atapci1
ata5: [ITHREAD]
pci0: <mass storage> at device 16.1 (no driver attached)
isab0: <PCI-ISA bridge> at device 17.0 on pci0
isa0: <ISA bus> on isab0
atapci2: <VIA 8233A UDMA133 controller> port 
0x1f0-0x1f7,0x3f6,0x170-0x177,0x376,0x6000-0x600f at device 17.1 on pci0
ata0: <ATA channel 0> on atapci2
ata0: [ITHREAD]
ata1: <ATA channel 1> on atapci2
ata1: [ITHREAD]
fdc0: <floppy drive controller> port 0x3f2-0x3f5,0x3f7 irq 6 drq 2 on acpi0
fdc0: [FILTER]
fd0: <1440-KB 3.5" drive> on fdc0 drive 0
sio0: <16550A-compatible COM port> port 0x3f8-0x3ff irq 4 flags 0x10 on 
acpi0
sio0: type 16550A
sio0: [FILTER]
sio1: <16550A-compatible COM port> port 0x2f8-0x2ff irq 3 on acpi0
sio1: type 16550A
sio1: [FILTER]
atkbdc0: <Keyboard controller (i8042)> port 0x60,0x64 irq 1 on acpi0
atkbd0: <AT Keyboard> irq 1 on atkbdc0
kbd0 at atkbd0
atkbd0: [GIANT-LOCKED]
atkbd0: [ITHREAD]
pmtimer0 on isa0
sc0: <System console> at flags 0x100 on isa0
sc0: VGA <16 virtual consoles, flags=0x300>
vga0: <Generic ISA VGA> at port 0x3c0-0x3df iomem 0xa0000-0xbffff on isa0
Timecounter "TSC" frequency 1668711970 Hz quality 800
Timecounters tick every 1.000 msec
ad0: 76319MB <WDC WD800BB-00CAA1 17.07W17> at ata0-master UDMA100
ad1: 58644MB <IC35L060AVER07 0 ER6OA46A> at ata0-slave UDMA100
ad2: 78167MB <Maxtor 6Y080L0 YAR41BW0> at ata1-master UDMA133
acd0: DVDR <HL-DT-ST DVDRAM GSA-4163B/A104> at ata1-slave UDMA33
ad8: 239372MB <Maxtor 6V250F0 VA111630> at ata4-master SATA150
Trying to mount root from ufs:/dev/ad0s1a
sis0: Applying short cable fix (reg=f1)

--
Bruce Cran