Why Barts is really VLIW4, not VLIW5 (and more on HD 5830/6790 being mainly 128-bit)

Sure, math doesn't lie (if used properly), but it can be used as part of a larger argument in which the non-math portions are flawed in some way.

How about with "the math doesn't prove it"?

I was going to mention this earlier, but I thought it was too obvious (plus I didn't know that it had to be in multiples of 64)….

 

From the other thread:

(Also, that seems like some math to me, as long as the performance results are in terms of numbers or similar stuff.)

 

*Ahem* OpenGL Guy works at AMD, in the driver development department (AFAIK). If anyone knows this stuff, it'll be him.

Barts is VLIW5. This is fact, it's not open to discussion, debate, or interpretation.

I think he's getting exasperated by you not listening to reason and instead insisting on clinging on to your personal opinions/delusions regardless of what anyone is saying.

You enjoy tilting at windmills, eh? How can you discuss that apples aren't in fact apples, but rather oranges? Seems less like a discussion to me and rather a stupid waste of time. Barts is VLIW5. End of story.

 

so after all that non math ( playing with a bunch of theoretical maximum numbers isn't the maths of it. Where is the accounting for the differences in the internal buses, changes in cache etc) how come you haven't answered

all your dodgy "math" aside how do you explain how transcendental are handled because it changed quite a bit between VLIW 4 and 5.

 

One does not need logic when he has facts.

And there are actually facts:

http://developer.amd.com/sdks/AMDAPPSDK/assets/AMD_Evergreen-Family_Instruction_Set_Architecture.pdf
It's named 'Evergreen' but it's actually for every gpu from R600 up to Evergreen/NI excluding Cayman.

http://developer.amd.com/sdks/AMDAPPSDK/assets/AMD_HD_6900_Series_Instruction_Set_Architecture.pdf
This one is specifically for Cayman

Look at the "Chapter 4: ALU clauses" in both and you'll find the info you need.

And as mczak already told you you could just look at the linux mesa drivers... Or ml.
You'd find posts like this one:
http://lists.freedesktop.org/archives/mesa-dev/2012-February/019495.html

It's coming from an vmware dev who actually writes low level gpu stuff.

 

You're using flawed data to dogy math, showing a spurious correlation, leading you to jump to an erroneous conclusion.

And you apparently lack the ability to comprehend the overwhelming evidence pointed out to you disproving your wild theory.

My poor statisticians heart aches reading this thread. It's like having _xxx_ back, except not in RPSC.

 

You have very "ignorant" (or naive) assumption that the ISA difference alone between the two VLIW architectures plays a pivotal role in whatever performance metrics you are flashing all over the place here. A GPU potential is still very much defined by a ton of dedicated graphics hardware in the pipeline, alongside the ALU throughput.
And no, the caching architecture in Cayman is pretty much the same as in the previous two generations.

 

Uhm, because Barts has a more efficient front-end to feed the available resources? I always thought Cypress was kind of a brute force approach of throwing more shaders into the card to achieve higher performance and wouldn't consider it a good example of an efficient VLIW5 GPU architecture. Law of dimnishing returns is a bitch and Barts shows this.

If you want to further hunt conspiracies, figure out how a GTX580 is so much faster than Cypress despite lower theoreticals.

 

Barts has among many other improvements:

- new front end, boosting utilization of shader core
- improved tesselation
- compared to 5830 fully functional 32 ROP's

On top of that game code rarely is limited by shader performance!
There are few purely shader limited tests, Perlin Noise from 3DMark is one of them. Just look at the results from this page and think about them for a second:
http://techreport.com/articles.x/20126/7

Barts performs exactly as you would expect from VLIW5 there.
Look at more complex tests to see how Barts is in line with Cypress on Particle, Cloth, and other tests where Cayman is showing good progress


Games are too complex workloads to just pinpoint any major similarities or differences between architectures. There might be 10% of the code running 300% faster on one architecture but 90% of code running a bit slower and you will get almost same speed on both of them. This kind of analysis is best done on low level code and synthetic benchmarks.
Game benches are great to establish how balanced architecture is for CURRENT workloads.

PS. You're not coming across as nice and polite person to me Bo_Fox but this might be my non native English. Try to listen with understanding more before going on crusade like seen in this topic.

 

Correct me if I am wrong, but isn't it all about shader utilization?

I did some calculations when the HD 7750 came out, and it turned out that it had like, 35% more performance per shader per clock than the HD 7950, which in turn is faster per shader per clock than the HD 7970 (looking at this card alone, it seems that GCN made no improvements in perf/shader).

And all of this on the same architecture.

If the HD 7970 had the same performance per shader than it's lower-end siblings, it would be much faster than even the previous dual-GPU cards.

I've it somewhere that it has much to do with the number of Asynchronous Command Engines (ACEs) on Tahiti, that is actually the same as with Cape Verde. Not sure though.

Maybe someone with more knowledge could explain it better?

 

Can i ask a noob question
vliw 5 i sort of understand 4 simple shaders + 1 complex
vliw 4 = 4 complex shaders
cgn is what ?

ps: about shader power the 2000 series had way much more shader power than its nv competition it but it wasnt until years later when the card was obsolete that the extra shading power helped framerate
(hope i got the right card)

 

I'm shocked that this thread made it to two pages overnight!

 

Im shocked at your maketing department Dave
look what i found from an amd slide

 

gcn, not cgn. vliw4 isn't exactly 4 complex alus, they are slightly more complex than the simple vliw5 ones as they need to perform the operations of the former complex alu but they need to work together for that.
For gcn, there's just one alu in that sense, with perhaps similar complexity to the ones in vliw4 (only looking at the shader alu itself, which doesn't really mean much, but anyway), since not multiple ones are working together for the more complex operations, but instead they need multiple clocks. I haven't actually seen a detailed analysis how fast these operations are on gcn.

HD2000 didn't actually have that much more shader power (not counting the SFU mul on 8800gtx, something like 30% more peak flops comparing hd2900xt to 8800gtx). I don't think this really ever helped that much with newer titles. Only starting with hd4xxx amd cards really had a huge peak flops advantage (often around 100%), since amd managed to cram in a lot more simds.

btw this thread is hilarious

 

thanks for that answer mczak, ive asked the question a couple of times but never really got an answer
so in simple terms vliw4 is groups of 4 while gcn are single entities ?