If i have two cards in Crossfire, can they be clocked at different speeds?

R

Robert_J

Limp Gawd
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Oct 24, 2009
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Say i have a regular xfx 5850 and i get a special msi 5850 with two fans that can overclock well

can the xfx run at standard speeds while the msi is overclocked?
 
they will run at the lowest common speed from what i recall
your oc'ed card will downclock itself to match the regular 5850
 
They run at the slower speed of the two cards.

Just overclock your slower 5850. Chances are it will overclock nearly as well as the MSI, if not better give or take depending on chip quality.
 
Everyone is wrong, so far. :p
- there is no downclock of the faster card to match anything

i am running a Diamond HD 5870 reference (850/1250) in CrossFire-X with a PowerColor HD 5870 PCS+ (875/1275) and EACH CARD *KEEPS* its OWN clockspeed.

You can adjust each cards's clockspeed *separately* in CCC if you like; that is the beauty of CrossFire-X that allows for a mismatch of clockspeeds; you can also CF-X a HD 5850 with a HD 5870 and it will be faster than CrossFired 5850s.
:cool:
 
Apoppin is correct in the fact that the cards are able to be clocked independently and still work in crossfire and none of the cards will change their clocks to match the others.

However... it will still load balance to the extent that each card will be doing an equivalent amount of work. If one card is more powerful you will actually see lower GPU utilization on that card compared to the weaker card.
 
GotNoRice said:
Apoppin is correct in the fact that the cards are able to be clocked independently and still work in crossfire and none of the cards will change their clocks to match the others.

However... it will still load balance to the extent that each card will be doing an equivalent amount of work. If one card is more powerful you will actually see lower GPU utilization on that card compared to the weaker card.
Click to expand...

i did a lot of testing last Summer with pairing combinations of HD 4870, 4870-X2 and 4890 in CrossFire-X

CrossFire-X, eXplored

Although there is load balancing, a FrankenFire "pair" of HD 4870/4890 in CrossFire-X is faster than a "true" CrossFired pair of HD 4870s but slower than a pair of HD 4890s. And a highly overclocked HD 4870 paired with a HD 4890(xOC) comes very close to the performance of true HD 4890 CrossFire.
 
From what I remember about these discussions, it turned out that all the cards *will* downclock to match the lowest clocked card, but that this downclock won't actually be visible to the user.
 
Raap said:
From what I remember about these discussions, it turned out that all the cards *will* downclock to match the lowest clocked card, but that this downclock won't actually be visible to the user.
Click to expand...

Link, please. My testing says otherwise,

There is way too much misinformation out on CrossFire-X
 
Raap said:
From what I remember about these discussions, it turned out that all the cards *will* downclock to match the lowest clocked card, but that this downclock won't actually be visible to the user.
Click to expand...

only SLI will do that I believe, not CF. since you can do multiple different card together for CF, but not SLI.
 
shansoft said:
only SLI will do that I believe, not CF. since you can do multiple different card together for CF, but not SLI.
Click to expand...

Ah yeah, could be it was about SLI. Am I correct in thinking that the memory clocks of the two cards in CF must match though?
 
You can run any clock speed on any ATI card in any combination of cards that ya want(5970/5850 below), and it will be fine.

Heres a screen of three different clocks playing farcry2,works fine.

744/1009
933/1197
850/1200

Ingame screen
 
Raap said:
Ah yeah, could be it was about SLI. Am I correct in thinking that the memory clocks of the two cards in CF must match though?
Click to expand...

SLi is far more restrictive. You cannot pair a GTX 280 with a GTX 285 nor a GTX 480 with a GTX 470 as examples. CrossFire-X allows for serious "mixing and matching".
-- i.e. You can CF-X HD 5850 with HD 5870 and/or HD 5970 and overclock each ones core and memory separately with CCC.

Here is the combination chart. Notice it says "recommended" .. you *may* be able to pair 5770 with 5870; you can pair HD 4870-X2 with HD 4830.

http://game.amd.com/us-en/content/images/crossfirex/CF_combo_chart.jpg

If you pair a slower card with a fast one in CrossFire-X, you will get better performance than with that single fast card in many cases as the second card "adds" to the performance by balancing some of the load. But if you stick a really slow card in with a fast one, it will not work properly.
 
Yep, I can confirm I had no issues running CF 5850's at different speeds. People seem to think the rules that apply to SLI apply to CF.
 
LeninGHOLA said:
Yep, I can confirm I had no issues running CF 5850's at different speeds. People seem to think the rules that apply to SLI apply to CF.
Click to expand...

I don't think that is really the main source of confusion here. It's pretty clear at this point that clocks aren't changing.

The remaining point of contention seems to be whether mixing uneven cards results in a performance boost over two of the slower cards, or to what degree Crossfire is able to balance the load between cards with different capabilities.

Now there are quite a few benchmarks on the net that do show crossfire slowing down to the "lowest common denominator" when using mixed cards, though there are also some user results such as those above that show Crossfire being able to take advantage of the faster card more than the slower card.

If anything this is the point that needs clarification, and preferably some idea of what is going on under the hood rather than conjecture based on user experiences.
 
GotNoRice said:
I don't think that is really the main source of confusion here. It's pretty clear at this point that clocks aren't changing.

The remaining point of contention seems to be whether mixing uneven cards results in a performance boost over two of the slower cards, or to what degree Crossfire is able to balance the load between cards with different capabilities.

Now there are quite a few benchmarks on the net that do show crossfire slowing down to the "lowest common denominator" when using mixed cards, though there are also some user results such as those above that show Crossfire being able to take advantage of the faster card more than the slower card.

If anything this is the point that needs clarification, and preferably some idea of what is going on under the hood rather than conjecture based on user experiences.
Click to expand...
Let me try again :p

i did a lot of testing last Summer with pairing combinations of HD 4870, 4870-X2 and 4890 in CrossFire-X

CrossFire-X, eXplored

Although there is load balancing, a FrankenFire "pair" of HD 4870/4890 in CrossFire-X is faster than a "true" CrossFired pair of HD 4870s but slower than a pair of HD 4890s. And a highly overclocked HD 4870 paired with a HD 4890(xOC) comes very close to the performance of true HD 4890 CrossFire.

If you follow the link, there are 17 pages that pretty much answer your questions.
 
apoppin said:
Let me try again :p
Click to expand...

I read your article.

Here is an article using newer cards and newer drivers and out of all the tests they did 5870+5850 was only faster than 5850 crossfire in one benchmark and that was well within the margin of error (I think it was like 300 vs 304 fps). In most cases, 5870+5850 crossfire was actually slower than 5850 crossfire.

http://www.legitreviews.com/article/1107/1/

Again, I value the work you've done to investigate this issue but the question is clearly not answered yet with any degree of clarity or certainty.

Could it be due to the different stream processor count in the 5850 vs. 5870 whereas 4870, 4890, and 4870x2 all have the same number of stream processors per GPU? That's just one question that is still out there.
 
GotNoRice said:
I read your article.

Here is an article using newer cards and newer drivers and out of all the tests they did 5870+5850 was only faster than 5850 crossfire in one benchmark and that was well within the margin of error (I think it was like 300 vs 304 fps). In most cases, 5870+5850 crossfire was actually slower than 5850 crossfire.

http://www.legitreviews.com/article/1107/1/

Again, I value the work you've done to investigate this issue but the question is clearly not answered yet with any degree of clarity or certainty.

Could it be due to the different stream processor count in the 5850 vs. 5870 whereas 4870, 4890, and 4870x2 all have the same number of stream processors per GPU? That's just one question that is still out there.
Click to expand...
First of all, i don't think you should benchmark with two CrossFire interconnects. :p

Secondly, they only tested *3* games
:rolleyes:

Thirdly, they only tested at 1920x1200 which does not stress 5850/5870 CF at all

What conclusions can you draw from 3 games that may be also CPU-dependent ?
:confused:

But you are right, it needs to be tested again .. properly. i am working on it as part of a series dealing with finding the limits of HD 5870 architecture
:cool:
 
apoppin said:
Thirdly, they only tested at 1920x1200 which does not stress 5850/5870 CF at all

What conclusions can you draw from 3 games that may be also CPU-dependent ?
:confused:
Click to expand...

Well they tested 5850 crossfire and 5870 crossfire. 5870 crossfire was faster than 5850 crossfire, as expected, so clearly there is room left for improvement with more GPU power.

If the resolution or lack of CPU power were the reason 5850+5870 is not faster than 5850 crossfire, then it would stand to reason that there would be little to no benefit from going to 5870 crossfire either.

Looking forward to reading your results.
 
GotNoRice said:
Well they tested 5850 crossfire and 5870 crossfire. 5870 crossfire was faster than 5850 crossfire, as expected, so clearly there is room left for improvement with more GPU power.

If the resolution or lack of CPU power were the reason 5850+5870 is not faster than 5850 crossfire, then it would stand to reason that there would be little to no benefit from going to 5870 crossfire either.

Looking forward to reading your results.
Click to expand...

Thanks. My point is that they simply didn't test it at all. Three games don't prove anything nor can they even show a trend - especially with 19x12 as the highest resolution; there simply isn't *that* much performance difference at all ... not between 5850 CF, 5870 CF and 5850+5870 CF-X.

You also have got to realize that my project is ongoing; it will take about 2 months to get the entire series out as it is a MASSIVE project spanning Dragon Platform vs. Core i7, as well as dual vs. quad with CPU and GPU scaling. Part 1 starts next week with a review of PowerColor HD 5870 PCS+ .. the one you are looking for is Part 4 or 5

:eek:
 
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