Bug#648222: Significant 2D performance regression with ColorTiling

[Michal Suchanek]

On 10 November 2011 17:46, Alex Deucher <alexdeucher at gmail.com> wrote:
> On Wed, Nov 9, 2011 at 12:36 PM, Iustin Pop <iustin at debian.org> wrote:
>> Package: xserver-xorg-video-radeon
>>
>> Version: 1:6.14.3-1
>> Severity: minor
>>
>> Hi,
>>
>> The recent upgrade of xserver-xorg-video-radeon from 1:6.14.2-2 to
>> 1:6.14.3-1 enabled ColorTiling for my card, which in turn caused a
>> significant performance degradation in 2D (yes, I understand it should
>> make 3D faster, but I didn't know it should slow down 2D applications).
>>
>> I'm using plain 2D environment (openbox, no compositing, anything) and
>> plain xterm (bitmap fonts, no AA, etc.). The speed of display text has
>> changed significantly enough that I can "see" my mutt refreshing the
>> inbox and drawing the lines.
>>
>> Cat-ing a big (~4K lines of text) file on a full-screen xterm is:
>>
>> - 6.14.2-2 (low power profile): ~0.8s
>> - 6.14.3   (high power)       : ~3.1s
>> - 6.14.3   (low power)        : ~5.0s
>>
>> So it's more than 5x time slower, which makes it "unpleasant".
>>
>> Simply disabling ColorTiling makes the problem go away, and 6.14.3 is as
>> fast as 6.14.2.
>>
>
> Tiling will speed up all rendering (2D and 3D).  However, it sounds
> like you are using an environment that is mostly software rendering.
> As such in order for the CPU to access tiled buffers, the GPU has to
> copy them to a linear buffer before CPU can access it properly.

FWIW I have color tiling enabled and have no speed issues in urxvt -
TrueType fonts, AA enabled, etc.

Unlike xterm urxvt (rxvt-unicode) uses some special font-rendering
libraries, however.

If I understand it correctly xterm would use the in-server bitmap font
rendering which the X server can accelerate as much as it wants.

Thanks

Michal