Re: [Xen-devel] [PATCH 6/6] Add MSI support to XEN

["Haitao Shan" <maillists.shan@xxxxxxxxx>]

Hi, Neil,

Please see my comments embedded.

2008/5/13 Neil Turton <nturton@xxxxxxxxxxxxxx>:
> I tried the latest unstable tree on a NIC which supports both MSI and
>  MSI-X.  When the driver was configured to use MSI mode, everything
>  worked fine but when it was configured to use MSI-X, the call to
>  pci_enable_msix succeeded but the interrupt didn't work.  Have these
>  patches been seen to work on an MSI-X device?
I have tested the patch using a NIC with both MSI-X and MSX
capabilities. I can successfully enable MSI-X for the NIC both in dom0
and in domU. The drivers I used for test is igb from
e1000.sourceforge.net.
Can you tell me how to reproduce your problem? Maybe there are some
pathes that I do not take care of. So that I can fix the problem.

>
>  In msix_capability_init (drivers/pci/msi-xen.c), there's a loop which
>  unmaps the old pirqs.  Shouldn't there be some similar code in
>  msi_capability_init?  I can't see any reason for the inconsistency
>  between the two functions.
Agree. I will add that.

>
>  Would it be possible to extend this code so that a PV backend driver
>  could map different MSI-X entries on a PCI device into different guests?
>  We already have frontend/backend drivers which allow multiple guests to
>  securely access the PCI memory of a single NIC and would like to extend
>  those drivers to map MSI-X interrupts directly to guests.  I
>  still don't understand enough about the new hypercalls to see how that
>  would work.
Do you mean your MSI-X capable NIC is owned simultaneously by multi
guests? Actually, I have not thought of this usage model. Currently,
we rely on pcibackend to provide the owner of the device. Yes, all
MSI-X interrupts are mapped to the same domain to which the device
belongs. But I think by properly set the dom_id for hypercall
PHYSDEVOP_map_pirq, it can cope wth such situations.

>
>  Cheers, Neil.
>
>
>
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