Re: [Xen-devel] [PV] PCI passthrough and interrupt sharing

[Chris <hap10@xxxxxxxxxxxxxx>]

Thomas Friebel wrote:
> When both NICs share the same IRQ, sooner or later host and
> guest networking both hang.

I'm having trouble reproducing this behavior.  My test setup contains
two physical NICs that share an IRQ.  Immediately after a fresh boot,
'cat /proc/interrupts' shows:

           CPU0       CPU1
 ...
 10:         74        489        Phys-irq  eth2, peth1
 ...

ACPI was disabled by appending 'acpi=off' to the dom0 kernel parameters.
 Similarly, IRQ sharing was caused by adding the "pirq=" dom0 kernel
parameter.

Then I used pciback late-binding to "hide" eth2 from dom0 and make it
accessible to domU.  After completing the late-binding process
(described in the users manual), /proc/interrupts gives:

           CPU0       CPU1
 ...
 10:    8408301        516        Phys-irq  peth1
 ...
 264:        93          0     Dynamic-irq  pciback
 ...

Apparently IRQ sharing no longer occurs after the pciback driver binds
to the device.  Let me know if this is what you observed.

With the NIC bound to pciback and domU started, I began the network
stress-tested as per your suggestion:

ssh <physical-guest-NIC> cat /dev/zero > /dev/null

After a long wait (it's been running for at least 15 minutes now)
connectivity in both dom0 and domU are (a bit sluggish but) still
working normally.

-Chris

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