Thank you very much for all your answers.
>Среда, 8 января 2020, 10:54 +03:00 от Oleksandr Andrushchenko <
>oleksandr_andrushche...@epam.com >:
>
>On 1/6/20 10:38 AM, Jürgen Groß wrote:
>> On 06.01.20 08:56, Santucco wrote:
>>> Hello,
>>>
>>> I’m trying to use vdispl interface from PV OS, it doesn’t work.
>>> Configuration details:
>>> Xen 4.12.1
>>> Dom0: Linux 4.20.17-gentoo #13 SMP Sat Dec 28 11:12:24 MSK 2019
>>> x86_64 Intel(R) Celeron(R) CPU N3050 @ 1.60GHz GenuineIntel GNU/Linux
>>> DomU: x86 Plan9, PV
>>> displ_be as a backend for vdispl and vkb
>>>
>>> when VM starts, displ_be reports about an error:
>>> gnttab: error: ioctl DMABUF_EXP_FROM_REFS failed: Invalid argument
>>> (displ_be.log:221)
>>>
>>> related Dom0 output is:
>>> [ 191.579278] Cannot provide dma-buf: use_ptemode 1
>>> (dmesg.create.log:123)
>>
>> This seems to be a limitation of the xen dma-buf driver. It was written
>> for being used on ARM initially where PV is not available.
>This is true and we never tried/targeted PV domains with this
>implementation,
>so if there is a need for that someone has to take a look on the proper
>implementation for PV…
Have I got your right and there is no the proper implementation :-)?
>>
>> CC-ing Oleksandr Andrushchenko who is the author of that driver. He
>> should be able to tell us what would be needed to enable PV dom0.
>>
>> Depending on your use case it might be possible to use PVH dom0, but
>> support for this mode is "experimental" only and some features are not
>> yet working.
>>
>Well, one of the workarounds possible is to drop zero-copying use-case
>(this is why display backend tries to create dmu-bufs from grants passed
>by the guest domain and fails because of "Cannot provide dma-buf:
>use_ptemode 1")
>So, in this case display backend will do memory copying for the incoming
>frames
>and won't touch DMABUF_EXP_FROM_REFS ioctl.
>To do so just disable zero-copying while building the backend [1]
Thanks, I have just tried the workaround. The backend has failed in an other
place not corresponding with dma_buf.
Anyway it is enough to continue debugging my frontend implementation.
Do you know how big is performance penalty in comparison with the zero-copy
variant?
Does it make a sense if I make a dedicated HVM domain with linux only for the
purpose of vdispl and vkbd backends? Is there a hope this approach will work?
>>
>> Juergen
>>
>[1] https://github.com/xen-troops/displ_be/blob/master/CMakeLists.txt#L12
Best regards,
Alexander Sychev
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