Tahiti's Bottleneck

[Lepton87]

We all know that 7970 has 2048 shaders and 7950 has 1792 shaders, that makes 7970 have over 14% more shaders yet at equal clocks the gap between the cards is far less then that, around 5%. Where's the bottleneck? It certainly isn't memory bandwidth as evidenced by tahiti LE performing on par with 7950 while having only 80% of its memory bandwidth. If someone didn't see tahiti LE benchmarks here there are http://www.computerbase.de/artikel/grafikkarten/2012/test-vtx3d-hd-7870-black-tahiti-le/4/

In many cases it's faster then non-boost 7950. Alas I think it's gonna be very a limited product akin to 6930 unless they have a huge stockpile of tahiti dice with less then 1792 shaders functional. What do you think?

 

[Olikan]

....arguably, the TDP/watt is a huge bottleneck for tahiti, this card have enought resources to reach >1.3Ghz with really good scalling

but i will point ROPs and TMUs as the problem

 

[aaksheytalwar]

Clock to clock the difference in fps where it really counts varies from 7-10%+ especially for min fps.

 

[Lepton87]

Clock to clock the difference in fps where it really counts varies from 7-10%+ especially for min fps.

Any links with the tests?

 

[Silverforce11]

Same as 5850 vs 5870, 6950 vs 6970.

ROP/TMUs.

 

[aaksheytalwar]

Any links with the tests?

Have a look at 5+ websites which compare minimum fps where both are below 60 fps and in recent games. Will prove itself if you google it

 

[Lepton87]

Have a look at 5+ websites which compare minimum fps where both are below 60 fps and in recent games. Will prove itself if you google it

There're no many tests where they test at equal clocks.

ROP/TMUs

not likely, especially TMUs

http://www.computerbase.de/artikel/grafikkarten/2012/test-vtx3d-hd-7870-black-tahiti-le/4/


See those tahiti le tests, it has less Texture (GT/s) and only 80% of memory bandwidth and is still roughly on par with 7950 otoh it has higher ROP performance. I wonder how much performance 7950 would lose if we equalized its bandwidth with tahiti le. That way the only visible difference would be ROP performance and of course tessellation performance and other things that scale with clock that we rarely consider like dispatch unit etc.

 

[aaksheytalwar]

You won't find same clocks. You will need to calculate and extrapolate.

 

[Termie]

I'm not sure what the answer is, but in my opinion, the 7950 is not a balanced card. Yes, sometimes a 7950 boost is about the same speed as a base 7970, but other times, it is much closer to the 7870. Therefore, given that the only advantage of a 7970 is shaders, you could come to the exact opposite conclusion as in the OP. It's all game-dependent.

 

[lavaheadache]

I think Tahiti's bottleneck is the shoddy driver team.

 

[aaksheytalwar]

I think Tahiti's bottleneck is the shoddy driver team.

And can you explain why isn't the 680 consistently significantly faster than the 670? The nvidia shoddy driver team?

 

[MTDEW]

I think Tahiti's bottleneck is the shoddy driver team.

I think we have a winner! :biggrin:

 

[lavaheadache]

I think we have a winner! :biggrin:

:biggrin:


seriously though.

 

[lavaheadache]

And can you explain why isn't the 680 consistently significantly faster than the 670? The nvidia shoddy driver team?

I'm not sure why you even mention nVidia in this thread. Are you looking for yet another new Red vs. Green battleground?

 

[aaksheytalwar]

The same reason why you talk something which is fictious.

 

[MTDEW]

:biggrin:


seriously though.

Oh i believe you are serious, that is what made it so funny.
I just bought a pair of 7950's, and wish i didnt.
And that is all i'm saying on here, otherwise this WILL turn into a red vs green thread.

 

[lehtv]

What's wrong with your 7950's? If it's microstutter, try radeonpro

 

[Leadbox]

I think it's the 7950's low clocks that spoil it, AMD had to put some distance between it and the 7970

 

[MTDEW]

What's wrong with your 7950's? If it's microstutter, try radeonpro

Thats the problem.
I have to cap the frame-rate to get smooth gameplay which negates the benefit of multi-gpu.
Single card - plays and performs great
Two in x-fire - well not so much

I thought at least far Cry 3 would be optimized for x-fire since its a Gaming Evolved Title.

And i'm not looking forward to Crysis 3, since it will NEED multi GPU's and i'm not holding my breathe on an x-fire profile/optimized driver on Crysis 3's launch.

I just don't think AMD's driver team has the resources to deal with all the high profile game releases in the 4th quarter every year.

Ok, i'm bailing from this thread.
All that is ever on VC&G anymore is red/green fighting.
And i want no part of it.

 

[p_monks33]

I agree with Lava, I believe if nvidia had the 7970 as their flagship card it would definitely be a better product on the software side. Amd's drivers aren't really bad, but they could use a lot of work when comparing them to nvidia. The bottleneck for me is in CCC crashing and triple monitor use and presets being a pain in the you know what. The 7970 is an absolute monster though.

 

[Lepton87]

After thinking about it more, I think that all in all tahiti is quite a balanced chip. If 14% increase in shader count brought similar increase in performance it would mean that shading power is the distinct bottleneck. One more indication that tahiti is a balanced chip is performance increase almost linear to corresponding increase in operating frequencies. 6970 didn't scale that well with clocks, kepler also don't scale that well with clock-speed. With that said there is always the weakest link. The architecture seems sound and I hope that GCN 2.0 will break 450mm2 barrier. I know, wishful thinking. Cayman was just slightly bigger then evergreen, why would this be different this time.

 

[BrightCandle]

I dont know. I am constantly disappointed with the performance of todays GPUs (NVidia and AMD) and I can't really explain why. Maybe its just the games are less well written for the hardware of the day.

 

[Maximilian]

So.... ROPS/TMU's it is then?

 

[thilanliyan]

I thought at least far Cry 3 would be optimized for x-fire since its a Gaming Evolved Title.

Read around, FC3 stutters...period.

Sometimes, stuttering is a game engine problem.

Like this:
http://forums.steampowered.com/forums//showthread.php?t=3022637

 

[Lepton87]

I dont know. I am constantly disappointed with the performance of todays GPUs (NVidia and AMD) and I can't really explain why. Maybe its just the games are less well written for the hardware of the day.

Me too, that's probably because since 2900XT failure ATi(AMD) ditched the big GPU die strategy and went for the sweet spot in terms of die size and performance. This generation nV realized that they can milk their mid tier GPU so releasing their big GPU as a GeForce would be bad for their profit margins. nV can both have slower and more expensive cards and still outsell AMD. (GTX680 comes to mind) nV calculated that they can earn more money by not releasing GK110 to the consumer market then by releasing it. That might change of course.
ps.

If I could get that kind of performance out of the box then I might bite.