[Qemu-devel] Qemu 2D performance plunges below acceptable levels

[Alexey Eremenko]

Hi All !

In KVM-84 I found that 2D performance simply plunges below acceptable
levels. It turned out to be Qemu bug (or "feature")

How To reproduce:
It is *very* visible if you work with remote X forwarding, using SDL
rendering. (where your Qemu server and local desktop are different
machines)
A. Qemu -boot n
This tried to initialize network boot from PXE. All the text rendered
moves very slowly on screen...
-or-
B. run Windows guest + Passmark Performance Test -> 2D Performance -> Fonts Test
-or-
C. run Windows guest -> Start -> Run -> cmd -> "tree C:\" command

Performance decrease is over tenfold -- so it is very visible with naked eye.

Now I have found the cause:
It is Qemu-git commit: 7d957bd8cbcbf56f7916d375e65042d767f544b5
"-DisplayState interface change (Stefano Stabellini) from 2009-01-15"

At last ! It took 2 days to figure it out !
First I had to bisect KVM-userspace git,
then I had to map KVM-userspace git commits to Qemu-git commits, as
they are not the same.
Finally I had to bisect Qemu git.

-- 
-Alexey Eromenko, 15.2.2009