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Re: [Xen-devel] pci adapter not working in dom0. works under plain Linux.

Tuesday, June 10, 2014, 3:08:32 PM, you wrote:

> On Tue, Jun 10, 2014 at 11:19:18AM +0000, James Harper wrote:
>> > 
>> > On Sun, Jun 08, 2014 at 11:01:25AM +0000, James Harper wrote:
>> > > I bought an unsupported DVB card (by mistake - I bought the v2 version
>> > instead of the supported v1 version), and I've just finished getting it 
>> > working
>> > under Linux, but spent the last day or so trying to figure out why it keeps
>> > dropping buffers even though the reception is perfect. As soon as I noticed
>> > that the lost data is always in PAGE_SIZE multiples, I figured I'd better 
>> > boot in
>> > plain Linux instead of Xen, and when I did that it worked perfectly.
>> > 
>> > What happens if you boot dom0 with 'dom0_mem=max:1G' and limit the
>> > amount of memory
>> > Xen sees by using 'mem=4G' on the Xen command line?
>> > 
>> That seems to make the problem go away. The machine itself has 5GB of memory 
>> in it, so (assuming an even spread) only 1/5 of allocations would come from 
>> >4GB memory right? This matches the missing pages of data in the resulting 
>> DMA transfers.

> That was my theory.
>> Where should I start looking for the fix? The card is PCIe so I would have 
>> thought it would have supported DMA to memory > 4GB, is that the problem? I 
>> think one of my USB devices has the same problem too.

> Ugh. They all should do the right job - that is using the DMA API.
>> Btw, what is dom0_mem=max:1G supposed to do? Dom0 still has ~3.7GB memory 
>> allocated to it on boot.

> Oh, I think I mentioned that it should have been on the 'dom0' line but
> I meant Xen line.

> If you try removing the 'mem=4G' and just use 'dom0_mem=max:1G' please?
> That should limit the amount of memory the dom0 uses (it sees the
> rest of the E820 - but does not use it) - and that means that the
> drivers should _also_ use said below memory.

> I had some preliminary patches for the V4L API to use a better
> DMA ops, but I fear that they are bitrotten (and I can't even
> find them!). But lets try first determine if the workarounds
> work for you.

Were you by any means referring to this thread / patch: 
http://lists.xen.org/archives/html/xen-devel/2012-01/msg01982.html ?


>> Thanks!
>> James

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