Re: GPU passthrough performance regression in >4GB vms due to XSA-60 changes

[Tomasz Wroblewski <tomasz.wroblewski@gmail.com>]

On 05/19/2014 01:01 PM, Jan Beulich wrote:
>>>> On 19.05.14 at 12:42, <tomasz.wroblewski@gmail.com> wrote:
>> Actually seems to be like the plausible explanation for the performance
>> issues we see could be that
>>
>> - some region of guest space has been relocated by hvmloader out to
>> 64bit memory to enlarge pci mmio hole (which stays in 32bit space)
>> - BUT the caching on that relocated region is UC since at the time of
>> the relocation MTRR was disabled and that caused the EPT entry to get UC
>> type.
> But this would be easily seen from 'D' debug key output - did you
> check this is what is the case?
Yes I've checked that, though I used some homebrew EPT dumping code 
instead. Mentioned it a bit earlier, in the original post as well as 
http://lists.xen.org/archives/html/xen-devel/2014-05/msg01965.html. I 
just incorrectly thought that it's the BAR being relocated which 
introduced some confusion..

> Jan
>