[Spice-devel] "qxl: add optinal 64bit vram bar" patch significantly slows down Spice

[Avi Kivity]

On 04/16/2012 12:39 PM, Gerd Hoffmann wrote:
> On 04/06/12 15:54, Hans de Goede wrote:
> > Hi Gerd,
> > 
> > While cherry picking some spice patches into my own qemu-kvm-1.0 branch,
> > so that we can add them to Fedora-17 I noticed a significant slowdown
> > after I was done cherry picking. Investigation has shown your
> > "qxl: add optinal 64bit vram bar" patch to be the culprit.
> > 
> > I noticed this using an old Fedora-14 32 bits vm with an xorg-x11-drv-qxl
> > patched to use the async methods.
> > 
> > If I scroll through the gnome applications menu with the mouse with
> > plain qemu-kvm-1.0 all is fine, but once I add your:
> > "qxl: add optinal 64bit vram bar" the updating of the display
> > becomes noticably slower, the blue bar highlighting the selected
> > menu entry becomes lagged compared to the mouse cursor.
>
> Avi?  This looks like a memory aliasing issue.
>
> Old state:
>   vram bar, backed by memory
>
> New state:
>   vram bar, 64bit, backed by memory, might not be mapped.
>   vram bar, 32bit, alias for the first part of the 64bit bar.
>
> Full patch:
>
> http://git.qemu.org/?p=qemu.git;a=commitdiff;h=6f2b175a090f367c3aab2226c4741b439671307a
>
> Any hints?
>

(qemu) info mtree
...
pci
...
  00000000fc022000-00000000fc022fff (prio 1): alias qxl.vram32 @qxl.vram
0000000000000000-0000000000000fff
...
qxl.vram
0000000000000000-0000000000000fff (prio 0): qxl.vram

Looks like both the BAR and it's backing region were initialized to 4k. 
The number 4096 does show up in the patch, probably it sneaked into the
BAR somehow.

-- 
error compiling committee.c: too many arguments to function