Confused by number of TMUs (NV G80)

[gszpetkowski]

The GPU-Z shows that my 8800 GTX has 64 TMUs, however associated TechPowerUp website indicates half of that:

http://www.techpowerup.com/gpudb/187/geforce-8800-gtx.html

Moreover, I think that both numbers might be incorrect. According to reference from NVIDIA's domain the G80 has only eight TMUs (Texture Mapping Units). Each of such unit is associated with two multiprocessors, that compose a TPC (eight clusters in total). Each TMU consist of:

• four Texture Addressing Units (TA)
• eight Texture Filtering Units (TF)

Hence, 64 would mean number of TFs and 32 number of TAs. Is that right?

References:
ftp://download.nvidia.com/developer/cuda/seminar/TDCI_Arch.pdf (page 54)
http://en.wikipedia.org/wiki/Texture_mapping_unit

 

[BiggieShady]

GPU-Z is right, TPU gpudb has an error to fix ... you should report it by clicking "Report an error" on the site

 

[MrGenius]

The "correct" number of TMUs is 8.

Texturing

• G80

• Every 2 SMs connect to a TMU (Texture Mapping Unit)

• 8 TMUs in total

• Each TMU contains 4 TA (Texture

Addressing) and 8 TF (Texture Filtering)

ftp://download.nvidia.com/developer/cuda/seminar/TDCI_Arch.pdf

TMU = 4 Texture Addressors + 8 Texture Filters

64 is completely wrong. And represents only the number of Texture Filters. Texture filtering is only part of what a TMU handles. Hence...GPU-Z is wrong! But it would be just as "inaccurate" to state 96(32 TAs + 64 TFs).

Though, 32 is closer to the truth. If we limit the meaning of the term "Mapping" to "locating texture mapped pixel coordinates in 3D space". For which the 32 Texture Addressors could be used. However, this doesn't meet the full definition of a TMU's function. Which also includes texture filtering operations.

 

[gszpetkowski]

GPU-Z is right, TPU gpudb has an error to fix ... you should report it by clicking "Report an error" on the site

Is it correct that definition of Texture Mapping Unit has changed between GT200 and Fermi? There is some discrepancy between those pages:

http://en.wikipedia.org/wiki/GeForce_200_series#GeForce_200_Series
http://en.wikipedia.org/wiki/GeForce_400_series#Products

The former states that number of TMUs is the same as number TFs (thus 80 for GTX 280 and 64 for G80), however the latter page uses number of TAs instead, thus only 64 TMUs in the fully-enabled GF100 (rather than 256).

The "correct" number of TMUs is 8.
...

Thanks for clear and definitive answer. I have also asked at NVIDIA's developer forum. Hopefully, they'll provide some answer as well.

Do you know how can I supply a bug report for GPU-Z?

 

[MrGenius]

It's about the most confusingly misworded conundrum I've ever come across. That's for certain. Who gets the right to determine the definition of a TMU, much less change it to mean something else? Who the hell knows I guess? I do comprehend the English language very well. And I tend to stick to the most widely accepted meanings of terms/words. Which would be that a TMU performs the functions of BOTH addressing and filtering textures. Regardless of the numbers of those components/parts comprising the unit as a whole. That's the only thing that makes any sense to me. It's not a TAU or a TFU...it's a TMU!!! AND IT MUST, AS A WHOLE/UNIT, BE CAPABLE OF HANDLING BOTH TEXTURE ADDRESSING AND TEXTURE FILTERING!!!

But whatever...I'm probably wrong. I just like pretending that I'm smart enough to figure it all out. When, in fact, I'm usually "only smart enough to get myself into a whole lot of trouble".

GPU-Z bug report? No...I haven't a clue.

 

[W1zzard]

By posting here you reported it.

 

[BiggieShady]

It's about the most confusingly misworded conundrum I've ever come across. That's for certain. Who gets the right to determine the definition of a TMU, much less change it to mean something else? Who the hell knows I guess?

Yeah, it successfully confused me