Re: [Xen-devel] PCI passthrough issue

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2011-02-01 at 23:01 +0000, Jean Baptiste Favre wrote:
> Le 01/02/2011 20:37, Konrad Rzeszutek Wilk a Ãcrit :
> > On Tue, Feb 01, 2011 at 04:23:09PM +0000, Ian Campbell wrote:
> >> 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
> > 
> > It could also have gotten the direction reverted (the 3c5XX code had it
> > wrong at some point so..). Might make sense to compile the kernel with
> > CONFIG_DMA_API_DEBUG  which is good at detecting these issues.
> > 
> >> 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
> > 
> > swiotlb=force will do it.
> OK, just performed native test.
> Installed 32bits Debian Squeeze, add 2.6.37 32bits kernel from
> experimental, setup grub with following options:
> "mem=256M swiotlb=force"
> 
> Ping tests work whatever can be packet size.
> 
> If I understood well what you explain to me, it's now clear that the
> problem is somewhat Xen related, isn't it ?

It certainly seems that way. I'm not 100% sure that swiotlb=force will
have actually made the driver use the swiotlb, it may just have forced
the swiotlb to be allocated. Konrad?

> I'll be able to continue any tests you want tomorrow.
> Do you still need me to compile domU kernel with "CONFIG_DMA_API_DEBUG"
> enabled ?

Yes please.

> If so, what tools will I need to get debug informations ?

Uh, Konrad?

Ian.


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