Thanks Pasi. Back to pci passthrough debugging.

I enabled nic interface via ifconfig and it doesn't receive any interrupts.
Driver in domU experiences tx timeout  and if I try to write to a disk in
domU(i.e cat /proc/interrupts > /root/debugs) system never recovers. From
dom0 cannot execute reboot/shutdown... have to use magic way to reboot the
system. I looked into xen-devel forum for any possible soln(patch mentioned
in the forum are all present in xen code I have). Inputs appreciated.

1. when dom0 is booted, device has irq 11 assigned

lspci -v on dom0

 Ethernet controller: Unknown device dead:face
        Subsystem: Unknown device dead:face
        Flags: bus master, medium devsel, latency 32, IRQ 11
        Memory at d0000000 (32-bit, non-prefetchable) [size=128M]

2. After domU boots up, irq is reassigned to 17 and it shares with usb/ide
disk and other devices
lspci -v on dom0

 Ethernet controller: Unknown device dead:face
        Subsystem: Unknown device dead:face
        Flags: bus master, medium devsel, latency 32, IRQ 17
        Memory at d0000000 (32-bit, non-prefetchable) [size=128M]

lspci -v on domU

00:00.0 Ethernet controller: Device dead:face
        Subsystem: Device dead:face
        Flags: bus master, medium devsel, latency 32, IRQ 17
        Memory at d0000000 (32-bit, non-prefetchable) [size=128M]
        Kernel driver in use: ncr2f
        Kernel modules: ncr2f

cat /proc/interrupts from domU

# cat /proc/interrupts
           CPU0
 17:          0  xen-pirq-pcifront  ncr2f0
502:       6336   xen-dyn-event     eth0
503:       2951   xen-dyn-event     blkif
504:        105   xen-dyn-event     hvc_console
505:         52   xen-dyn-event     pcifront
506:        351   xen-dyn-event     xenbus
507:          0   xen-dyn-ipi       callfuncsingle0
508:          0   xen-dyn-virq      debug0
509:          0   xen-dyn-ipi       callfunc0
510:          0   xen-dyn-ipi       resched0
511:       5949   xen-dyn-virq      timer0
NMI:          0   Non-maskable interrupts
LOC:          0   Local timer interrupts
SPU:          0   Spurious interrupts
PMI:          0   Performance monitoring interrupts
PND:          0   Performance pending work
RES:          0   Rescheduling interrupts
CAL:          0   Function call interrupts
TLB:          0   TLB shootdowns
TRM:          0   Thermal event interrupts
THR:          0   Threshold APIC interrupts
MCE:          0   Machine check exceptions
MCP:          0   Machine check polls
ERR:          0
MIS:          0

After around 50 secs...

# cat /proc/interrupts
           CPU0
 17:          0  xen-pirq-pcifront  ncr2f0
502:       7283   xen-dyn-event     eth0
503:       2951   xen-dyn-event     blkif
504:        121   xen-dyn-event     hvc_console
505:         52   xen-dyn-event     pcifront
506:        351   xen-dyn-event     xenbus
507:          0   xen-dyn-ipi       callfuncsingle0
508:          0   xen-dyn-virq      debug0
509:          0   xen-dyn-ipi       callfunc0
510:          0   xen-dyn-ipi       resched0
511:       6237   xen-dyn-virq      timer0
NMI:          0   Non-maskable interrupts
LOC:          0   Local timer interrupts
SPU:          0   Spurious interrupts
PMI:          0   Performance monitoring interrupts
PND:          0   Performance pending work
RES:          0   Rescheduling interrupts
CAL:          0   Function call interrupts
TLB:          0   TLB shootdowns
TRM:          0   Thermal event interrupts
THR:          0   Threshold APIC interrupts
MCE:          0   Machine check exceptions
MCP:          0   Machine check polls
ERR:          0
MIS:          0