Re: [Xen-devel] PCI passthrough issue

[Jean Baptiste Favre <xen-devel@xxxxxxxxxxx>]

Le 01/02/2011 20:37, Konrad Rzeszutek Wilk a écrit :
> 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 ?

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

Now, it's time to sleep here in France :) (or I'll get killed by my girl
friend :D )

Regards,
JB

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