Re: [Xen-devel] PCI passthrough issue

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2011-02-01 at 15:38 +0000, Jean Baptiste Favre wrote:
> OK, just found it:
> after domU boot:
> - log in
> - ping -s 86 10.0.0.1 (fails)
> - rmmod sky2
> - modprobe sky2 copybreak=0 (no packet copied)
> - ping -s 86 10.0.0.1 (works)
> 
> So it's clearly related to that option.

Awesome!

> Now the question: what am I supposed to do ?

I think the next step is to try and reproduce on native 32 bit, with RAM
artificially limited via the mem= kernel command in option, this will
let us determine if this is a generic issue or is somehow Xen specific.

The main difference caused by the copybreak option is that for larger
frames (i.e. always when copybreak==0) it hits a code path which uses
pci_map_single and pci_map_page to access the received data. When len <
copybreak it takes a path which uses pci_dma_sync_single_for_cpu, so it
seems like the later path is broken somehow. If the issue does turn out
to be related to Xen then I think that points to the swiotlb code.

I assume you are not seeing "rx mapping error" in your domU dmesg? Did
you post a full guest console log at some point? Comparing the logs for
the 256MB, 398MB and 512MB guest RAM case might be useful.

Konrad, is there some way to force swiotlb use even for native to make
the native test cases more relevant? Or is there some other direction we
should try first?

> It seems that adding this options in /etc/modprobe.d/sky2.conf does not
> work, neither using /etc/modules

That will be a userspace issue in your distro, perhaps with openwrt they
are not expected to work that way.

Ian.



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