Trifire 7750's

[ruhtraeel]

A silly idea came to my head today...

A10 6800k/Kaveri (Kaveri with the same # of SP's as a 7750) + two 7750's?!?

It would be cool if it didn't suffer from stutter, 7970 performance for the price of a 7970 without a CPU if it all went swimmingly

IMO the only practical thing about this would be trying to build a near 0 decibel gaming PC with passive cooling

 

[Yuriman]

Couple of problems -

1. HD7750 doesn't have a crossfire bridge

2. Kaveri has extremely limited memory bandwidth for the amount of stream processors - I'd expect it to lose 40% or more performance from that

3. An HD7970 is approximately 4 7750's in one die, not 3

4. Crossfire scaling

 

[zir_blazer]

Usually, you worst enemy when trying to run any sort of assymetric setup are the Drivers, *EVEN* when you're not trying to use the GPUs in Crossfire (Just as standalone Coprocessors for GPGPU stuff like BitCoin mining, Drivers are also a pain in the butt). Proper multiGPU scaling depends 100% on Drivers. Besides, I think that Asymetric Crossfire only officially supports the integrated GPU + some low or mid range Video Card, not two. You may not get it to work. And with the current sttutering status of Crossfire... Why bother?

Want passive cooling? You will need something very custom. Either a very, very good aftermarket passive heatsink that you can use to replace the standard one, or a custom, non-reference card that already comes with such a thing. Underclocking and undervolting also works and you will pretty much have to do it regardless anything else. It should be possible to pick a Radeon 7970, and check how its scales down to see if you can drastically cut power consumption without sacrificing too much performance. Indeed, you may end up purchasing a 7970, and losing 30-40% performance to get it to power consumption levels where you can passively cool it, but it will still be a single card.

 

[ruhtraeel]

Couple of problems -

1. HD7750 doesn't have a crossfire bridge

2. Kaveri has extremely limited memory bandwidth for the amount of stream processors - I'd expect it to lose 40% or more performance from that

3. An HD7970 is approximately 4 7750's in one die, not 3

4. Crossfire scaling

Crossfire on the 7750 is done on the mobo, not through a crossfire bridge.

I wouldn't imagine a Kaveri + 2 7750's to be viable, but I think if they got Kaveri with one 7750 to perform decently, it would be a good alternative for something like a mITX build.
If a Kaveri APU is close to a 7750, adding another 7750 might get around 7870 performance. Could make for a cheaper mITX build, with a cheaper mobo vs LGA 1155

But yeah from what I've heard, the memory bandwidth on Kaveri isn't great.

 

[Durvelle27]

Crossfire on the 7750 is done on the mobo, not through a crossfire bridge.

I wouldn't imagine a Kaveri + 2 7750's to be viable, but I think if they got Kaveri with one 7750 to perform decently, it would be a good alternative for something like a mITX build.

one of the worst ideas considering you can get a better single card for the same price or even cheaper. I would never crossfire lower end cards as its not worth it. Just get a single HD 7870 XT and call it a day. If you want passive they have a few 7850s that are

 

[Enigmoid]

A silly idea came to my head today...

A10 6800k/Kaveri (Kaveri with the same # of SP's as a 7750) + two 7750's?!?

It would be cool if it didn't suffer from stutter, 7970 performance for the price of a 7970 without a CPU if it all went swimmingly

IMO the only practical thing about this would be trying to build a near 0 decibel gaming PC with passive cooling

A10 kaveri may bottleneck a 7970 under cpu demanding games (BF3, Crysis 3, etc).

Low Vram (1 GB isn't enough).

From newegg.

http://www.newegg.com/Product/Produc...82E16814127709

$90 2GB 7750

7870 - $170 with rebates

http://www.newegg.com/Product/Produc...82E16814202025

7870 is the better bet

 

[Stuka87]

A10 kaveri may bottleneck a 7970 under cpu demanding games (BF3, Crysis 3, etc).

Low Vram (1 GB isn't enough).

From newegg.

http://www.newegg.com/Product/Produc...82E16814127709

$90 2GB 7750

7870 - $170 with rebates

http://www.newegg.com/Product/Produc...82E16814202025

7870 is the better bet

Very few games are going to peg out a 4GHz+ quad core. BF3 gets very close with a busy 64 player server. But OC the CPU a bit and it should be fine.

But I agree that CF 7750's is a waste. Maybe if you already had one 7750, then doing CF with the built in GPU may make sense. But its not going to be that fast.

 

[Enigmoid]

Very few games are going to peg out a 4GHz+ quad core. BF3 gets very close with a busy 64 player server. But OC the CPU a bit and it should be fine.

But I agree that CF 7750's is a waste. Maybe if you already had one 7750, then doing CF with the built in GPU may make sense. But its not going to be that fast.

Its a 4 GHz Kaveri quad (not ivy/haswell), my guess is add about 10-20% onto trinity/richland at the same frequency. And yes a 4300 (which has L3) will bottleneck a 7970 pretty bad in BF3 MP, also in games such as Crysis 3 or CPU heavy mmo games (gw2 comes to mind).

 

[Bateluer]

Seems dumb when you could spend less money on a single card, get more performance and avoid any issues related to multi-GPU set ups while likely using less power.

 

[Yuriman]

Crossfire on the 7750 is done on the mobo, not through a crossfire bridge.

I wouldn't imagine a Kaveri + 2 7750's to be viable, but I think if they got Kaveri with one 7750 to perform decently, it would be a good alternative for something like a mITX build.
If a Kaveri APU is close to a 7750, adding another 7750 might get around 7870 performance. Could make for a cheaper mITX build, with a cheaper mobo vs LGA 1155

But yeah from what I've heard, the memory bandwidth on Kaveri isn't great.

HD7750 - 512SPs, 128bit GDDR5 @ 1125mhz
HD7850 - 1024SPs, 256bit GDDR5 @ 1200mhz
HD7870LE - 1536SPs, 256bit GDDR5 @ 1500mhz
HD7950 - 1792SPs, 384bit GDDR5 @ 1250mhz
HD7970 - 2048SPs, 384bit GDDR5 @ 1375mhz

^ From this we can glean that two 7750 GDDR5's in Crossfire can be expected to, with perfect scaling, perform close to a single HD7850 1GB. Three add up to approximately a single HD7870LE (Tahiti core) with a hair more memory bandwidth and half the RAM. An HD7970 is essentially four HD7750's together on one die and 3x the RAM.

The problem here is scaling of price - you can get an HD7850 1GB for $130 on Newegg right now, while Tahiti LE is priced at $230. The cheapest 7750 is $80 on Newegg, which means you get (512/80) = 6.4 stream processors per dollar, as compared to 7.9 and 6.8 with the 7850 and 7870LE respectively. Then toss in Crossfire scaling and frame pacing issues.

Some cards it makes sense to Crossfire, and some it doesn't.

Kaveri would only make sense in Crossfire if the it had 4.8ghz 128bit GDDR5 supplying its iGPU, and it were priced at no more than $50 more than an equivalent 2-module chip including RAM costs (Athlon 750K = $75 so we're looking at a $135 upper bound), and had perfect Crossfire scaling. Unfortunately, we can expect Kaveri's iGPU to perform somewhat closer to a DDR3 7750 which is only about 60% as fast on average as the GDDR5 version, which (on paper) puts dual HD7750 + Kaveri TriFire in at 90% the theoretical performance of a single HD7850 1GB.

That said, Kaveri will probably still be the best solution for anyone who can't add a discrete GPU for whatever reason.