Tri SLI and what card to use as master

[ibpalle]

Hi all

I'll be taking my watercooled system apart over the next couple of weeks to rebuild it with a different airflow configuration. At the same time I want to move the gfx cards about as I have found out that the bottom 8xPCI-E slot holds the master card in a tri-SLI configuration, not the top 16xPCI-E that I expected.

Each card is connected to a 24" monitor for a surround setup.

Now, I have 3 cards that each behave differently.

C1: Ocuk(Palit) gtx680. Consistently runs 26MHz core above the 2 others. Power usage approx +7-9% higher than the others. Temp 4-5c above the others
C2: Zotac gtx680. Runs same speed as C3. Uses 2% more power than C3. runs 1-2c hotter than C3.
C3: MSI gtx680. 48c on load. core 1100Mhz.

So the question now is which card to use as master. Here is what I came up with:

Top PCI-Ex16 : Sync with Master : MSI : PhysX card
Middle PCI-Ex8: Sync with Master : Zotac
Bottom PCI-Ex8: Master : Ocuk

It looks to me like the master card runs one or two percent below what the sync cards does possibly due to the sync cards having to keep in sync with the master. I have tried finding info about this on google but cant really find anything about the so I have not confirmed thats how it works. If it does then putting the Ocuk card in the master slot at the bottom would free it from having to keep in sync, releasing a few % to raise the baseline as it were.

MSI card goes in the x16 slot and gets designated as the physx card. Its the coolest running card so should be better able to cope with physx and also, gets the x16 slot because of that.

Zotac card goes in the middle on the remaining x8 slot.

If the master - sync relationship does not work as I assume above then the positioning could be different. If the master card has the highest workload then the MSI card needs to be in the bottom slot....

Decisions, decisions....

Anyways - hope someone has a few pointers on what, if any, performance differences there are between a master and the sync systems in tri-SLI.

 

[spoffle]

I don't think SLi uses the "master" and "slave" way it used to.

 

[OptimaLnrg]

How have you determined which card is the 'master'? (8x slot)

 

[whyscotty]

which motherboard ?

 

[ibpalle]

MB is a P6X58D-E. And looking at the info sheet from from MSI kombustor it appears things have changed since I last looked at it - or I have just made a fool of myself.

GPU1 (Ocuk in x16 slot)
________________________________________________________________________________
Display device : GeForce GTX 680 on GK104 GPU
Display driver : 310.70
BIOS : 80.04.09.00.01
GUID : VEN_10DE&DEV_1180&SUBSYS_096910DE&REV_A1&BUS_3&DEV_0&FN_0
Multi-GPU role : master

GPU2
________________________________________________________________________________
Display device : MSI N680GTX series on GK104 GPU
Display driver : 310.70
BIOS : 80.04.47.00.03
GUID : VEN_10DE&DEV_1180&SUBSYS_28201462&REV_A1&BUS_4&DEV_0&FN_0
Multi-GPU role : synchronized with master

GPU3 (Zotac)
________________________________________________________________________________
Display device : GeForce GTX 680 on GK104 GPU
Display driver : 310.70
BIOS : 80.04.09.00.01
GUID : VEN_10DE&DEV_1180&SUBSYS_125519DA&REV_A1&BUS_5&DEV_0&FN_0
Multi-GPU role : synchronized with master

In gpuz the ocuk card shows up as number 2, Zotac as number 1 and MSI as the third. All very confusing. Anyways - top x16 slot now has master ard and the Ocuk card is in there but would it be better to get the MSI in there?

 

[OptimaLnrg]

I generally don't trust kombustor to get anything right. I couldn't get it to stress both cards in sli anyway.

Imo one of your cards is boosting higher because it has a better core. I don't think there's any point moving them around though. A lot of hassle for no good reason.

..unless it's only the cpu on watercooling and the gpus have different cooler designs?

 

[ibpalle]

No, the cooling is the same on all cards. An EK Nickel-Plexi block on each.

I'll keep them as is then. Performance wise its all good. Just checking if I had missed a trick somewhere

 

[OptimaLnrg]

what i do wonder actually, is how the frames for each display are negotiated when the displays are connected to different gpus?

Because with crossfire you can only use the connections on 1 gpu, I assume because that's the 'master', whereas here the 'master' must be collecting a completed frame and then sending it to a different gpu for output to display?

would that induce the possibility of micro-stutter? or am I rambling BS?

 

[ibpalle]

Good question Back to google for a bit...