Overclocking SLI cards

[wrugoin]

From what I've read about SLI videocards, they have to be the exact same cards. I'm not too sure about brand names, but I know that you can't SLI a 6600GT and a 6800GT together. (I can only guess because there'd be uneven distribution of the workload)

This got me thinking. This board is filled with a lot of enthusiasts that love to OC their videocards. Would you be able to have two cards in SLI if once they're overclocked, they run under different clock or memory speeds. Meaning, if you overclock them, do you have to overclock them to the same GPU & Memory speeds?

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Sony DRU-510A DVD-RW<P ID="edit"><FONT SIZE=-1><EM>Edited by wrugoin on 10/24/04 03:12 PM.</EM></FONT></P>

 

[georgebeee]

says here:

"It is up to the add-in-card partner to determine if they follow NVIDIA’s reference designs for SLi support.

NVIDIA does not support SLI on two different models or from different vendors. SLI supports configurations with the same model (i.e. 6800 Ultra) from the same vendor (Vendor XYZ).

SLI is designed for PCI Express and not AGP. This new bus has superior bandwidth (two to four times AGP 8X), support for isochronous data transport, and the capability to drive multiple high-speed graphics devices. AGP 8X is limited to one high-speed graphics device and is not a good candidate for SLI."

copied that from Nvidia's website

 

[georgebeee]

so, I guess that answers half your question. I posted a note asking them for more information about SLI OC'ing. we'll see if they respond

 

[TheGreatGrapeApe]

Well it seems pretty abovious that you'd want similar clock speeds, anything out of whack would cause one half of the screen to get 45fps and the other half to get 42fps. That kind of thing would not only be noticeable but would likely also cause problems with the drivers (synching up frames if ones able to process faster. I suspect they will have enough problems with getting the drivers to work in enough games (heck they still have issues with just one card [like the others]) that adding out of synch cards may just compound problems. It would be similar to why you don't want different cards doing it different scene processing speeds.

It'll be interesting to see the official line on the issue though.

- You need a licence to buy a gun, but they'll sell anyone a stamp <i>(or internet account)</i> ! - <font color=green>RED </font color=green> <font color=red> GREEN</font color=red> GA to SK

 

[priyajeet]

they will have something like a failsafe built into the driver. Need to match the two FPS. Like make the FPS = min of the two.

:tongue: <A HREF="http://www.geocities.com/priyajeet/fing.jpg" target="_new"><i><font color=red>Very funny, Scotty.</font color=red><font color=blue> Now beam down my clothes.</font color=blue></i></A> :tongue:

 

[TheGreatGrapeApe]

And thus overclocking one card above the other would net no benifit, constantly measuring the FPS isn't as easy as simply saying clock A = clock B.

Of course it'll be interesting to see how it deals with complex rendering situations where the sky is empty (render a plain blue space) and yet the bottom half of the screen has tons of work to do.

Well we'll have to wait a while and see what happens. It'll be interesting to see how it does across a wide variety of games and whether it's as difficult to program for as the runtime compiler was, where you may have to wait a bit for driver updates before you get the full benifit.


- You need a licence to buy a gun, but they'll sell anyone a stamp <i>(or internet account)</i> ! - <font color=green>RED </font color=green> <font color=red> GREEN</font color=red> GA to SK

 

[priyajeet]

true, but then we'll be using two same cards. If we can OC one, we can do it to the other. Ofcourse keeping heat/power into consideration.
You are right, its too early to talk of this, it even hasnt hit the production machines yet. And looking at the shortage these days SLI will hit the consumer door only by next year.

:tongue: <A HREF="http://www.geocities.com/priyajeet/fing.jpg" target="_new"><i><font color=red>Very funny, Scotty.</font color=red><font color=blue> Now beam down my clothes.</font color=blue></i></A> :tongue:

 

[TheGreatGrapeApe]

If we can OC one, we can do it to the other.

You're missing the point, I'm not saying you can't OC both cards, but that OC'ing them out of phase per say would cause problems. That was the question in the original post. It is HIGHLY unlikely both cards would have the same maximum speeds, so it would be interesting to see what happens when they are out of sync.

nV says SLI will be here by next month. I think that more paper pushing, but we'll see. it quite possible that we'll see ALOT of SLI, but most likely implementations will be GF6600s except for reviewers and bungholio braggers.


- You need a licence to buy a gun, but they'll sell anyone a stamp <i>(or internet account)</i> ! - <font color=green>RED </font color=green> <font color=red> GREEN</font color=red> GA to SK
<P ID="edit"><FONT SIZE=-1><EM>Edited by TheGreatGrapeApe on 10/24/04 01:19 AM.</EM></FONT></P>

 

[RichPLS]

I would imagine that out of sync would mean that data would wait for slowest card to catch up. So you would just get a hit on the optimum performance expected.
I imagine threads would split processing, and to display them all processess would need to be complete before displaying.

_____________________________________________
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[RichPLS]

I would imagine that out of sync would mean that data would wait for slowest card to catch up. So you would just get a hit on the optimum performance expected.
I imagine threads would split processing, and to display them all processess would need to be complete before displaying.

_____________________________________________
<font color=red> And the sign says "You got to have a membership card to get inside" Huh
So I got me a pen and paper And I made up my own little sign </font color=red>

 

[wrugoin]

Of course it'll be interesting to see how it deals with complex rendering situations where the sky is empty (render a plain blue space) and yet the bottom half of the screen has tons of work to do.

and

anything out of whack would cause one half of the screen to get 45fps and the other half to get 42fps

How exactly does SLI work. I was under the impression that it rendered ever other line on the screen, but from this it seems like each GPU renders half the screen (top/bottom)

From my little text example, how does SLI work?

note GPU 1 = X, GPU 2 = O

Sample A.
XXXXXXXXXXXXXXXXXXXXXXXXXXXXX
OOOOOOOOOOOOOOOOOOOOOOOOOO
XXXXXXXXXXXXXXXXXXXXXXXXXXXXX
OOOOOOOOOOOOOOOOOOOOOOOOOO
XXXXXXXXXXXXXXXXXXXXXXXXXXXXX
OOOOOOOOOOOOOOOOOOOOOOOOOO
XXXXXXXXXXXXXXXXXXXXXXXXXXXXX
OOOOOOOOOOOOOOOOOOOOOOOOOO
XXXXXXXXXXXXXXXXXXXXXXXXXXXXX
OOOOOOOOOOOOOOOOOOOOOOOOOO

Sample B.
XXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXX
OOOOOOOOOOOOOOOOOOOOOOOOOO
OOOOOOOOOOOOOOOOOOOOOOOOOO
OOOOOOOOOOOOOOOOOOOOOOOOOO
OOOOOOOOOOOOOOOOOOOOOOOOOO

Thanks for any help,
Mike.



---MY RIG---
MSI Nforce2 w/ Athlon XP 1700+
512MB PC-2700 Kingmax
Geforce 2 GTS (*blush*)
WD800JB 80GB,IMB 20GB
USB 2.0 WD 15GB HDD
Pioneer 16X Slot DVD
Sony DRU-510A DVD-RW

 

[priyajeet]

sample B.
see ALX video array here
<A HREF="http://www.alienware.com/ALX_pages/main_content.aspx" target="_new">http://www.alienware.com/ALX_pages/main_content.aspx</A>

SLI will be working in the same way.

:tongue: <A HREF="http://www.geocities.com/priyajeet/fing.jpg" target="_new"><i><font color=red>Very funny, Scotty.</font color=red><font color=blue> Now beam down my clothes.</font color=blue></i></A> :tongue:

 

[TheGreatGrapeApe]

According to the demos out there it splits the screen in two. Top and bottom.

I'll see if I can find the examples again, where it shows the work of just the one card.

Here's the [H] pics that shows the load balancing, shich may assume that it somehow determines that one can do more of the screen than the other so somehow it'd do a 60/40 split to take advanatage of the top/bottom bias.

<A HREF="http://www.hardocp.com/image.html?image=MTA4ODIyMTcyN2dhRndFYWhCUU1fMl8xMV9sLmpwZw==" target="_new">http://www.hardocp.com/image.html?image=MTA4ODIyMTcyN2dhRndFYWhCUU1fMl8xMV9sLmpwZw==</A>

I think the video was from a demo in Deadmonton Alberta. I posted it a while back.


- You need a licence to buy a gun, but they'll sell anyone a stamp <i>(or internet account)</i> ! - <font color=green>RED </font color=green> <font color=red> GREEN</font color=red> GA to SK

 

[TheGreatGrapeApe]

Of course that's ALX not SLI, but they do look similar.



- You need a licence to buy a gun, but they'll sell anyone a stamp <i>(or internet account)</i> ! - <font color=green>RED </font color=green> <font color=red> GREEN</font color=red> GA to SK

 

[wrugoin]

Ahhh, thanks for the info. After some research, I found that the "every other line" process for SLI was a 3Dfx (voodoo2) approach, whereas Nvidia splits the screen top to bottom and uses dynamic balancing.

I'm just thinking, Greatgrapeape, you mentioned that you might find great unbalance when rendering sceens where you have sky and ground, and the ground half requires much more processing power. Wouldn't you think that if they split the screen vertically instead, they'd find less of an occsasion to dynamically balance the GPU load?

---MY RIG---
MSI Nforce2 w/ Athlon XP 1700+
512MB PC-2700 Kingmax
Geforce 2 GTS (*blush*)
WD800JB 80GB,IMB 20GB
USB 2.0 WD 15GB HDD
Pioneer 16X Slot DVD
Sony DRU-510A DVD-RW<P ID="edit"><FONT SIZE=-1><EM>Edited by wrugoin on 10/24/04 05:03 PM.</EM></FONT></P>

 

[georgebeee]

isn't there a connector between the 2 cards? isn't it possible for the one card not to start on the next frame until they both finish the frame they are on? does one card start at the top and the other at the bottom and neither card move on to the next frame until they meet in the middle?

 

[spitoon]

isn't there a connector between the 2 cards? isn't it possible for the one card not to start on the next frame until they both finish the frame they are on? does one card start at the top and the other at the bottom and neither card move on to the next frame until they meet in the middle?

That's kind of how I was picturing it...the fact that they are connected together by the SLI bridge may over-rule many of the changes you can make...for example, in the control panel for SLI'd cards you would only have one setting for AA, controlling both cards, and one setting for Vsync, again controlling both cards...the same could be done for clock frequencies, so they are both running at the same speed...in the event that someone puts two different cards together (or changes the BIOS) the clocks would default to the slower speed. Sounds like a lot of work for the driver...