r200 exa performance regression in xserver-1.6?

[Simon Thum]

> I did a quick sysprof test while switching desktops, and it looks like
> it's all in memcpy:
> 
> miClearToBackground                                         0.00  77.45
>   miPaintWindow                                             0.00  77.45
>     ValidateGC                                              0.00  77.45
>       In file /usr/bin/Xorg                                 0.00  77.45
>         In file /usr/lib/xorg/modules/libexa.so             0.00  77.45
>           exaPrepareAccessGC                                0.00  77.45
>             exaPrepareAccess                                0.00  77.45
>               exaPrepareAccessReg                           0.00  77.45
>                 exaDoMigration                              0.00  77.45
>                   In file /usr/lib/xorg/modules/libexa.so   0.00  77.45
>                     memcpy                                 77.45  77.45
This looks a lot like what I had when I did not properly compile it to 
use DRI. Make sure DRI is available.