R9 290(x) crossfired thru PLEX CHIP

[Ja.KooLit]

Is it a good idea to run a crossfire 290 (x) thru PLX chip?

Would there be a performance impact?

I have been searching all over net but all I can find are crossfired 290(x) with X79 mobos........

This is a question from a friend and I am just helping him to find an answer....


his rig z87 sniper 5 with 4770K

 

[buildzoid]

It might screw with frame pacing but other than that it should be perfectly ok.

 

[Ja.KooLit]

It might screw with frame pacing but other than that it should be perfectly ok.

Thanks could you elaborate more? I know for the fact that frame pacing of this cards are thru hardware...... I also thought about that but my own guess, only guess is that theoritically, it should be better because it will be filtered the video rendering thru PLEX chip.... its like a 2 rivers going into single river going to open SEA, (CPU)..... but that is just what I thought. I would want to see thru bench of course or personal experience......

He is also searching and searching though, I have more time searching thru internet.....


edit: He has same monitor resolution as mine 2560 x 1600..... we were actually thinking of buying one more 2560 x 1600 monitor and test if 290 crossfired can be able to handle games in

4800 x 2560 (portrait) or 7680 x 1600 resolution...... but both of us dont have 2011 CPU and mobo..... ^_^

 

[buildzoid]

The thing with PLX chips is that they don't make more lanes they do traffic management to make it look like there are more lanes. So traffic on the PCI-e goes form this:

GPU1 >> PCI-e 3.0 x8 >> CPU >> PCI-e 3.0 x8 >> GPU 2

to this:

GPU1 >> PCI-e 3.0 x16 >> PLX >> PCI-e 3.0 x16 >> CPU>> PLX >> PCI-e 3.0 x16 >> GPU 2

and according to the PLX website every pass through the PLX chip takes up another 110 nano seconds. In the diagram there are 2 passes through the PLX, off setting frame times by an extra 220ns which is such a big deal so you should be fine.

 

[Ja.KooLit]

ok ok... i know about PLX chips...... i do know also that they dont make more lanes......


what I am after now is that the R9 290 (non X) and R9 290X use PCI-E lanes to communicate each other.....

Theoretically, There is a big performance impact since now if there is PLX chip involve. Imagine like this........

2 person (2 R9 290) calling a company (CPU). but company uses a HUB (PLEX Chip). Unlike with no HUB, it can directly contact company....

Before, GPU's are communicating thru Xfire Bridges....

as to performance impact? Nobody knows unless somebody will really do extensive test.


as for PLEX chip, 220 nano seconds doesnt impact really on game performance.

Anandtech did an extensive test.

http://www.anandtech.com/show/7189/choosing-a-gaming-cpu-september-2013/6

look at Metro 2033. I7-4770K, 3 7970's using PLX has atleast 2 more FPS compared to 3930K, 3 7970's........

I know i know the games are old but that is just an example........


7970's uses bridge, R9 290's using PCI lanes........

That is what I am after for now.....

 

[buildzoid]

The 2FPS difference between the 3770k and 3930k is the fact that a 3770k is faster in single threaded tasks and has nothing to do with the PLX chip. Basically the PLX chip will be slower than native PCI-e by XXX nano seconds. In Xfire the PCI-e bus is used for shipping rendered images from the second card to the first and for the first to tell the second when to start working. The moving of a raw 1080p image over PCI-e 3.0 x16 takes 377ns from the second card to the cpu and another 377ns from the CPU to the first GPU. With the PLX you just add the delay that the PLX takes to re route and add it to both the GPU2 to CPU and CPU to GPU1 transfer and you get the effect of the PLX chip on the frame rate. The PLX chip on your mobo takes 126ns to reroute so it adds 252ns to the time between new frames which is so little that you won't ever notice.
So Xfire r9 290s over PLX is perfectly OK.

 

[Ja.KooLit]

The 2FPS difference between the 3770k and 3930k is the fact that a 3770k is faster in single threaded tasks and has nothing to do with the PLX chip. Basically the PLX chip will be slower than native PCI-e by XXX nano seconds. In Xfire the PCI-e bus is used for shipping rendered images from the second card to the first and for the first to tell the second when to start working. The moving of a raw 1080p image over PCI-e 3.0 x16 takes 377ns from the second card to the cpu and another 377ns from the CPU to the first GPU. With the PLX you just add the delay that the PLX takes to re route and add it to both the GPU2 to CPU and CPU to GPU1 transfer and you get the effect of the PLX chip on the frame rate. The PLX chip on your mobo takes 126ns to reroute so it adds 252ns to the time between new frames which is so little that you won't ever notice.
So Xfire r9 290s over PLX is perfectly OK.

Thanks. logically yes it should work. I ask Ian of Anandtech, (thanks Ian for the quick reply) and he said it should be perfectly ok.....

I wish there is return policy here in Korea but the fact that once it was opened, no return but I can exchange if there is a problem.

He just dont want to pull the trigger yet cause of this return policy. without a firm evidence that it should work........

 

[Ja.KooLit]

bump? anybody who has more input?

 

[Arjai]

IDK, but, sounds like you could take GPU 1 and cover it in chocolate, GPU 2 and cover it in Peanut butter. In theory, according to Hoyle, it would only add 114ns to the PLX chip total. Meaning the transfer rate would still be quicker than the time between when you think you are gonna sneeze, and you close your eyes...to sneeze.

Much quicker.

 

[Ja.KooLit]

IDK, but, sounds like you could take GPU 1 and cover it in chocolate, GPU 2 and cover it in Peanut butter. In theory, according to Hoyle, it would only add 114ns to the PLX chip total. Meaning the transfer rate would still be quicker than the time between when you think you are gonna sneeze, and you close your eyes...to sneeze.

Much quicker.

of course it is much quicker....

its just I am after if there is a huge difference between running them PCIE3 x 8 (dual) directly connected to CPU.

and a crossfired 290's thru PLX chips

 

[Arjai]

I know you wanted a second opinion, I just goofed off but, from buildzoid 's description... timings should not be an issue. However, if you are like me, less IS more.

So, in theory, fewer gates, fewer hinges to oil.

Hmm, mayhaps I can think of a few more obscurities to describe something as obviously as I can....

 

[Ja.KooLit]

Appreciate it by trying to explain more. There is no need for you to do it. I got the logic. But actual impacts is what I am after for.....

look for example 290's vs 780's..... 290's has more bandwidth than gtx 780's. but, its always like that. NVIDIA cards has always less band width than AMD. and all benches is neck to neck comparison with todays games and apps. Its not like head vs toes difference.

But now there is a PLX involve. would there be a performance impact now that 290's are sharing infos with these PLX? Who knows until somebody has actually do a very intensive testing....

IF only, here in korea, there is a 30 days return, I will test it myself once I got hold with the mobo I like with PLX chip..... But rules here is that once you bought it, no return. I can exchange but with same type not different type.....

So........ before actually pulling trigger on 290's I just want to read some benches....

In that way, I can decide if its a good idea to get 290's xfire or tri fired or even quad fire with PLX chips mobos

 

[Arjai]

In my opinion, as a non tech, is that it unlikely you will have a major meltdown running on a PLX. It may not be the ultimate bandwidth setup, however, it does appear, if what buildzoid 's statements are true, that there will be a minor nanoseconds difference and will be a nice upgrade, despite the blower fan noise.

Perhaps, YOU will be the one doing an extensive review of the 290's xfired on a PLX?

 

[Ja.KooLit]

well I can but I dont have 780ti's to compare or other cards to compare

Paging AMD and NVIDIA please lend me 2 or 3 290x and 2 o3 780ti's so I can have extensive review about these gpu's with PLX involve