X.Org Server Change Allows GLAMOR To Fallback To Software Rendering For Obsolete GPUs

[Eirikr1848]

And to be somehow more precise this change is important mainly for the very first D3D9 hardware generation which came with Shader Model 2.0. Those GPUs had support for only 64 ALU instructions while later Shader Model 2.0a and Shader Model 2.0b had support for 512.

In the end this affects predominantly Intel iGPUs of the third and one model of the fourth generation, ergo the GMA 900 up to GMA 3150 models. From ATI/AMD only the original R300 series aka Radeon 9550 to 9800 GPUs were affected. All later Radeon GPUs came with Shader Model 2.0b or newer.

Nvidia isn't affected by this because their D3D9 GPUs always came at least with Shader Model 2.0a and had therefore always support for 512 ALU instructions.

However, this doesn't mean that Glamor works out of the box on ATI Radeon R400 and Nvidia NV30+ hardware. As of April 2024 Glamor works only for R500 ergo Shader Model 3.0 based hardware while the development for R400 is ongoing. Regarding Nvidia NV30 and NV40 hardware the state of Glamor is unfortunately quite unclear. Probably this is because the nv30 nouveau driver is in a not so good condition, - compared with he r300 driver.

GLAMOR doesn’t work on my Dell Vostro 1000 with Radeon Xpress 200 AKA Radeon Xpress 1100/1150 (reported as both). It’s an RV480 but only has 64ALU and GLAMOR I believe requires 128.

Does this mean it will use the 64 ALU + software to “augment” those to create a hybrid software/hardware solution or is it strictly software-only?

[ReaperX7]

I can see where in the server space, many motherboards using older GPU chipsets like Rage128 for basic rendering would benefit from this without throwing driver errors and such.

[jlm400]

However, this doesn't mean that Glamor works out of the box on ATI Radeon R400 and Nvidia NV30+ hardware.

A couple of years ago I had sold my graphics card to buy a new one and didn't have an iGPU, but I had a Geforce 7200 GS (from 2006!) lying around, so I put that in my computer. Surprisingly, it worked flawlessly out of the box, aside from performance on composited window managers.

[lorn10]

Linuxhippy
The main problem on R400 Radeon hardware seems to be a limited "loop unrolling" capability. For more details simply check the corresponding Mesa MR 28630.

Eirikr1848
As far I known there are only a small amount of Glamor shaders which are problematic. One of those is described as "gradient shader" and that one will be processed then in software. So I think you will still have hardware accelerated Glamor shaders in most cases even on RV480 hardware.

Finally, the best would be if those problematic Glamor shaders could be completed with a GLES2 alternative. So this would mean that we would have two types of gradient shaders, one GLES2 compliant and the other GLES3+. The current state is (as of April 2024) that Glamor claims that it is GLES2 compliant while it simply isn't 100% GLES2 conformant.

[oiaohm]

I can see where in the server space, many motherboards using older GPU chipsets like Rage128 for basic rendering would benefit from this without throwing driver errors and such.

Many server motherboards you find aspeed

https://www.aspeedtech.com/server_ast2500/

https://www.aspeedtech.com/file/support/Aspeed%20Graphics%20User%20Guide.pdf

This is not older GPU chipset this is 2020 part. Yes a modern 2d only display output device found in many server motherboards found as BMC ("Base Board Management Controller") to allow you to remote control the computer.

There are other BMC with equal as bad display outputs displayed to OS with somewhere between no GPU and very poor GPU. When I say very poor GPU I mean GPU that look very much stone aged for functionality even compared to Rage128 and these are all GPU designs under 10 years old. Yes the aspeed closest historic item is your old VGA graphics cards yes this is as in 1987 level functionality well before the Rage128.

Server space still has items that are before GPU designs. Yes VGA out ports on some new motherboards are serous-ally 1987 level vga on a 2024 made motherboard.

You have mix of very old GPU designs with mix of pre GPU designs done modern(like the aspeed) with somewhat modern GPU thrown in for good measure integrated into new server motherboards. This is true mess of a problem space.

[MrCooper]

Just in time for Xwayland 24.1

I can see where in the server space, many motherboards using older GPU chipsets like Rage128 for basic rendering would benefit from this without throwing driver errors and such.

glamor can't accelerate anything with a GPU which doesn't have pixel shaders. So this will allow glamor to work with R300-R500 generation Radeons, not older ATI GPUs though.

[oiaohm]

Just in time for Xwayland 24.1

glamor can't accelerate anything with a GPU which doesn't have pixel shaders. So this will allow glamor to work with R300-R500 generation Radeons, not older ATI GPUs though.

https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/956

Not quite there are cases where you end up with llvmpipe with a GPU less like aspeed hidden behind virgl these days due to patch above. It might be idea to detect llvmpipe on virgl again for this software rendering depending on cost of the software rendering..

This virgl stuff is not items people normally think about it does make things a little less black and white.

[dec05eba]

decades of bloat and removal of "obsolete optimizations" plus blending 2d images in shaders instead of dedicated fixed function pipelines, ... ¯\_(ツ)_/¯

One reason is also the difference in resolution. A difference in resolution affects cpu performance much much more than gpu performance