AMD Fusion On Gallium3D Leaves A Lot To Be Desired

[phoronix]

Phoronix: AMD Fusion On Gallium3D Leaves A Lot To Be Desired

It's been a few months since last running any AMD Fusion tests under Linux, so here's a look at the AMD A8-3870K "Llano" APU performance under both the latest Catalyst driver and the open-source Radeon Gallium3D stack with Ubuntu 12.04. Besides the open-source driver being handily beaten by the Catalyst binary driver, the power efficiency is also a disappointment.

http://www.phoronix.com/vr.php?view=17255

[Qaridarium]

VLIW... without a better shader compiler the radeon driver don't have any chance.

and amd is not planing to build a shader compiler based on obsolete technique.

the hd7970 will get a proper shader compiler.

in other words opensource divers needs 3-4 years more time to catch up. -


RIP- VLIW...

[log0]

OK. I don't meant this as a criticism on driver developers. I am sure they are doing their best. And I've got no idea about writing device drivers. But I am wondering how it is possible that one implementation is an order of magnitude slower than another. Is it the complex hardware interface? Or is OpenGL so broken making it so difficult to write fast, efficient drivers? Is the nouveau approach to reverse-engineer a well performing driver maybe the better approach(assuming that a faster driver exists)?

[Drago]

OK. I don't meant this as a criticism on driver developers. I am sure they are doing their best. And I've got no idea about writing device drivers. But I am wondering how it is possible that one implementation is an order of magnitude slower than another. Is it the complex hardware interface? Or is OpenGL so broken making it so difficult to write fast, efficient drivers? Is the nouveau approach to reverse-engineer a well performing driver maybe the better approach(assuming that a faster driver exists)?

The thing is that, nvidia had until kepler, sheduler in hardware, and thus it optimizes shareders itself, rather than relying on driver code to to that(in case of AMD VLIW). With GCN AMD integrated hardware sheduler, so performance gap will shrink.

[darkbasic]

Shader compiler *isn't* the culprit, desktop cards are ~50/60% of catalyst while this shit is two orders om magnitude slower

[Death Knight]

Aaah, Phoronix forget to set "GPU clock to LOW", which is AMD's advice for PM issues on open source stack!
Look at this thread also...

[marek]

OK. I don't meant this as a criticism on driver developers. I am sure they are doing their best. And I've got no idea about writing device drivers. But I am wondering how it is possible that one implementation is an order of magnitude slower than another. Is it the complex hardware interface? Or is OpenGL so broken making it so difficult to write fast, efficient drivers? Is the nouveau approach to reverse-engineer a well performing driver maybe the better approach(assuming that a faster driver exists)?

The problem is lack of manpower. r600g needs like another 5 developers working full-time to make sure the driver works best - adding new features, fixing bugs, profiling and identifying the bottlenecks and optimizing the driver. So far developers have been mostly adding new features and fixing bugs when they had time. Optimizations must be done in the entire stack, including shared components like core Mesa.

I wonder if Michael enabled 2D tiling.

[log0]

I see. What I am wondering about is why do graphics card drivers require this amount of manpower? Is it the hardware or the API? How is it possible to write driver code that could be more than ten times faster? Or is it that the hardware doesn't map to the exposed API(OpenGL) and requires complex translation? Sorry if the questions sound silly, I've never worked with bare hardware.

[clavko]

Open source driver seems roughly the same level of performance
as open source driver for Intel's SB graphics. I guess one should
really use Catalyst. If your card is supported, though.

[pingufunkybeat]

I see. What I am wondering about is why do graphics card drivers require this amount of manpower? Is it the hardware or the API? How is it possible to write driver code that could be more than ten times faster? Or is it that the hardware doesn't map to the exposed API(OpenGL) and requires complex translation? Sorry if the questions sound silly, I've never worked with bare hardware.

N.B. I'm not a driver developer, just an interested observer

In this case, the open source driver was forced into a low-power mode, while the proprietary driver was going on at full blast. Also, it's possible that not all functionality (such as tiling) was enabled on the open source driver. When there's an order-of-magnitude difference, then either something is wrong, or the driver is too new and there's lots of work needed still.

The problem with OpenGL drivers (and GPU drivers in general) is that they are amazingly complex hardware that takes incredible amounts of code (especially full OpenGL support). It's much more complex than a network card driver or a mouse driver. With most chips, the Gallium3d drivers for radeons are around 60-70% of the proprietary driver, which is as close as you can get with "regular" effort.

Then the things get complicated. A GPU driver runs on the CPU and often has to do many things before it can prepare a frame for rendering. If it is not optimised, then the time adds up, lots of little delays all over the stack, which need to be optimised one-by-one, hundreds of them. This is very time-intensive and takes a lot of manpower. If you are running something at 100 frames per second ,then this quickly adds up and makes a huge difference. Even a small delay multiplied by 100 becomes a long wait. That's why the developers are first focusing on getting a driver working correctly, and only then try to optimise it.

With some work, and Tom's VLIW packetiser and the new shader compiler, and the Hyper-Z support, things should come to more than 80% of the proprietary performance, perhaps even more (rough guess). That's really good, and the additional work after than becomes too complex, with very little gain.