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HD7870 Crossfire questions.

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December 30, 2012 5:47:41 PM

Alright, so right now I got an ASRock B75M-GL motherboard and The Gigabyte HD7870 OC graphics card, along with an i5-3330 CPU.

I really want to be able to crossfire at some point (sooner rather than later), and sadly now, I realize that my motherboard runs in PCI-e 3.0 16x/2.0 4x mode, which sucks. Any idea on what kind of performance loss? I saw a benchmark which stated that the HD7970 had a ~6% loss in 2.0 4x mode.

My PSU is a Coolermaster 620 W.

I also did not know that the i5-3330 can't be overclocked. I can live with that, but it worries me if that also means it will easily bottleneck. Any ideas in that respect?

More about : hd7870 crossfire questions

December 30, 2012 5:51:47 PM

I would also like to add that I run 2 monitors at 1680x1050 resolution. These are run on VGA only, which means not grabbing a second graphics card either means getting a new screen or a HDMI to VGA adapter, which also factors into my decision to get the second card, since I already have 2 DVI to VGA sticks.
a b V Motherboard
December 30, 2012 6:03:47 PM

Hi :) 

Buy a 7990 (and a bigger 850 psu)

I did... its brilliant...

All the best Brett :) 

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Anonymous
a b V Motherboard
December 30, 2012 6:20:18 PM

seems you may have already seen this:


the question is are you willing to deal with that until you get a proper (x8, x8) motherboard?

i may not be entirely correct but i think that means a Z75/77. not sure how many B75 or H77 have x8, x8.
December 30, 2012 8:13:21 PM

Brett928S2: I just bought my HD7870, so upgrading to that is out of the question. My main idea was to be able to upgrade into crossfire.

looniam: That is exactly the chart I've seen. But the strange thing is, when I read up on crossfire on here, it seems as if the loss is more like ~25%? This was reported from a previous family of the HD series, however.

But a 6% loss I can live with, until a motherboard upgrade. I am worried, however, how this loss of performance will translate into a crossfire setup. I believe I won't see a 200% performance in 8x/8x regardless, probably more in the area of 150-180%. But being in 16x/4x I might see much less of a performance boost, than simply 6% less.

Would the 4x-slot card not drag down the 16x-slot, like how a 7850 would drag down a 7870? Making it in effect, 4x/4x speedwise? Or reducing the crossfire perfomance by 12%? According to one article on here, the general loss in 16x/4x mode was ~10%, and on rare occasion closer to ~25%.

Yes, I afak it would have to be Z77 or Z75, if I want PCIe 3.0 as well. I've found one or two boards with other chipsets and 2.0 8x/8x. Sadly, it seems almost all of them are slightly too expensive for me, when combined with buying another 7870, although one could always hope for a drop in price.

Also, any info on the issue with microstutter in regards to the 7xxx-series and crossfire setups?

And I still wonder if my i5-3330 is enough.

Thanks for the responses. :) 
Anonymous
a b V Motherboard
December 31, 2012 12:20:17 AM

LoveTrain said:

looniam: That is exactly the chart I've seen. But the strange thing is, when I read up on crossfire on here, it seems as if the loss is more like ~25%? This was reported from a previous family of the HD series, however.

But a 6% loss I can live with, until a motherboard upgrade. I am worried, however, how this loss of performance will translate into a crossfire setup. I believe I won't see a 200% performance in 8x/8x regardless, probably more in the area of 150-180%. But being in 16x/4x I might see much less of a performance boost, than simply 6% less.

Would the 4x-slot card not drag down the 16x-slot, like how a 7850 would drag down a 7870? Making it in effect, 4x/4x speedwise? Or reducing the crossfire perfomance by 12%? According to one article on here, the general loss in 16x/4x mode was ~10%, and on rare occasion closer to ~25%.

Yes, I afak it would have to be Z77 or Z75, if I want PCIe 3.0 as well. I've found one or two boards with other chipsets and 2.0 8x/8x. Sadly, it seems almost all of them are slightly too expensive for me, when combined with buying another 7870, although one could always hope for a drop in price.

i think maybe you comparing apples to oranges looking a the bandwidth performance with a Xfire performance gain. i mean we could play with numbers a little bit and speculate that the card itself would have 94% performance but since it is 50% of a Xfire set up then your loss of performance is 3% and not 6%.

after looking around for a bit i found a few things:
Crossfire x16,x4 vs x8,x8 Comparison
a discussion thread where the OP had ~9% increase benhmarking x16,x4 to a x8 x8.

but looking here:
CrossFire x8/x8 or x16/x4: The Ongoing Dilemma
the results of performance difference weren't nearly as pronounced in games as in a synthetic benchmark.

now i do like the conclusion:
Quote:
Conclusion: If you have a CrossFireX-compatible motherboard, and you’ve just realised that x16/x4 is the only PCI Express scenario available to you, don’t feel left out at all. Stick that second graphics card in and enjoy better performance without any worries as to the efficiency of your new system.


the results will depend on what game(s) and how well it(they) Xfire along with what resolution your are gaming at. i would suggest thinking about going for it; worst case scenario is you will get a substantial increase in performance, not perfect but substantial.



hope this helped.
December 31, 2012 1:02:00 AM

Thank you for the reply! It seems it's not that huge a performance hit, although it's hard to find anything on the 7xxx-series, as most benchmark comparing the two setups are with 5xxx-series and 6xxx-series. I think I'll buy the GPU somewhat soon and see how it goes.

The micro stuttering still worries me though, and I wonder if the 7xxx-series handles that better than previous series. Also any idea on the CPU-bottleneck aspect? Is the i5-3330 strong enough for 2x7870's?

Again, thanks for your time.
a b V Motherboard
December 31, 2012 2:33:56 PM

LoveTrain said:
Thank you for the reply! It seems it's not that huge a performance hit, although it's hard to find anything on the 7xxx-series, as most benchmark comparing the two setups are with 5xxx-series and 6xxx-series. I think I'll buy the GPU somewhat soon and see how it goes.

The micro stuttering still worries me though, and I wonder if the 7xxx-series handles that better than previous series. Also any idea on the CPU-bottleneck aspect? Is the i5-3330 strong enough for 2x7870's?

Again, thanks for your time.



Hi :) 

For what its worth I get no micro stuttering on my 7990 , but both gpus are on one card, which is probably what makes the difference...

All the best Brett :) 
Anonymous
a b V Motherboard
December 31, 2012 6:54:06 PM

as far as any bottleneck from the i5-3330; i have my doubts it would and if it does i again doubt it would be significant. both the cpu and motherboard are very limited with any overclocking, practically none. you *could* raise the Bclk slightly by 5% (insert warning here) but that won't lead to a very noticeable gain while playing but every little bit may help.


warning: increasing the Bclk also affects the PCI bus and RAM speed; they are used to/spec'd for a 100Mhz timing. raising it 10% (110Mhz) or beyond has been known to cause some severe instability issues and possibly damage components. increasing it by 5% or less will decrease the likelihood of this happening.

however beware of the risks and slowly increase the speed by 0.5 Mhz in steps and test w/Prime95 to insure stability.

though to sum it up about microstutter or bottlenecking issues. you really won't know until you try Xfiring those 7870s. on the whole; this look pretty good for you to be able to NOT have any big issues; so i think it not a bad idea to try it out and see what happens.
a b V Motherboard
January 1, 2013 11:16:25 PM

Quote:
*** off Brett. No one wants a 7990 so go drive away in your Porsche to Harvard and buy some degrees.



Hi :) 

You REALLY NEED to read Toms rules about personal insults.... and I already have a couple of degrees , thank you...

REPORTED...........

All the best Brett :) 
January 2, 2013 12:37:09 AM

Cool it. This is a legit discussion, so let it run its course so the OP can get the info he is after.
January 3, 2013 8:41:18 AM

Yea, I think I'll leave the BCLK at what it's at, and avoid messing with that. Seems more trouble than what it's worth.

I'll have the second card Tuesday, so I think I'll try out some benchmarks etc. then and report back. Maybe someone else will be able to use what I learn. Seems there's quite scarce actual information regarding my setup/similar setup.
January 3, 2013 11:09:08 AM

my i5 3470 have feature to raise the clock 400Mhz with motherboard "non-k processor overclock" function (or is it all ivy bridge feature?). The multiplier can reach 38x with all core (3.8Ghz) and 40x with one core (4GHz). That feature surely will make your processor have a slightly better life before it bottleneck some GPU (maybe 3-4 years later, lol, that quite long!)
!