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

[Tomasz Wroblewski <tomasz.wroblewski@xxxxxxxxx>]

On 05/15/2014 03:39 PM, Tomasz Wroblewski wrote:
> On 05/15/2014 03:23 PM, Jan Beulich wrote:
> > > > > On 15.05.14 at 14:10, <tomasz.wroblewski@xxxxxxxxx> wrote:
> > > Not really sure why it only affects 64bit vms but I've just noticed the
> > > pci BARs for the card are being relocated by hvmloader as per some 
> > > logs:
> > > (XEN) HVM3: Relocating guest memory for lowmem MMIO space enabled
> > > (XEN) HVM3: Relocating 0xffff pages from 0e0001000 to 14dc00000 for
> > > lowmem MMIO hole
> > > (XEN) HVM3: Relocating 0x1 pages from 0e0000000 to 15dbff000 for lowmem
> > > MMIO hole
> > >
> > > So it might be also related to that.
> > Indeed it might - what are the (guest) MTRR types for those regions?
> It's writeback for both the 32bit and 64bit above ranges.
... however, after a bit more debugging its uncached at the time 
hvmloader does the relocation so that's why it ends up like that in EPT 
tables. It does go to writeback only soon after. Haven't pinpointed the 
exact time point for that yet nor why it's being updated to writeback, 
but it seems to be before the guest starts booting (i.e. still on bios 
screens).
> > Jan

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