Question for Those Running SLI & a Third Card for PhysX

Joined
Nov 15, 2006
Messages
30
I tried asking this on the Nvidia forums but surprisingly cannot get a straight answer. I'm wondering if anyone else out there is using three video cards - two in SLI and one for PhysX - without any issues with the PhysX card being recognized.

I can dedicate the third card (a GeForce GTX 750) to PhysX in the Nvidia control panel and it seems to work fine. However, if I reboot - this card is no longer recognized as a dedicated PhysX card nor is it even selectable anymore in the Nvidia control panel.

So what I have to do is one of two things. I can either disable then reenable SLI - at which point the GTX 750 magically reappears in the control panel as a dedicated PhysX card. Or I can disable/reenable the GTX 750 in Device Manager to get the same effect.

I'm puzzled why I would need to do this as the GTX 750 appears to be just fine in Device Manager when I boot. It seems like it could be a driver issue (I'm currently using 353.30), but the problem occurs with older drivers as well. So now I'm starting to wonder if it could even be related to my motherboard somehow (a Gigabyte GA-X99-UD3P).

In order to help diagnose the problem, I would really like to know if anyone with a similar arrangement using three video cards is not having this problem. That would tell me it's likely not driver-related.

Of course, if anyone has a solution to this problem that would be just Jim Dandy :D but I can't find anything anywhere on the internet on how to fix this.
 

wirk

Gawd
Joined
Sep 2, 2014
Messages
811
I missed your previous post. I happen to have 2x Titan X and a GTX 970. So just for playing with stuff I allocated the GTX as PhysX in addition to the Titan X SLI. It seems to work perfectly, the problem is I can not see any difference anywhere with the PhysX enabled. I am using latest drivers now but I think it would work fine with the previous drivers too.

Do you have 3 identical cards? Maybe this is the problem?
 
Joined
Nov 15, 2006
Messages
30
Thanks for checking Wirk.

So as long as your configuration continues to show your GTX 970 as a dedicated PhysX card after you reboot then yeah - sounds like your setup works just fine. I'm also using two Titan X's as well. Was planning on switching out my third card for a GTX 950 Ti whenever they become available but not sure if that will make a difference.

If the issue was my motherboard I would think my third card would not show up correctly in Device Manager so I'm completely baffled. For now, I just have to always remember to do that toggle off/on trick to get it to show up right as the PhysX card.
 

NoOther

Supreme [H]ardness
Joined
May 14, 2008
Messages
6,468
I have had the same problem in the past, I had to keep re-enabling the PhysX card. Honestly though, I didn't see much overall benefit to having the SLI + PhysX card. I just up my SLI cards and let them run PhysX if I want it.
 

wirk

Gawd
Joined
Sep 2, 2014
Messages
811
Thanks for checking Wirk.

So as long as your configuration continues to show your GTX 970 as a dedicated PhysX card after you reboot then yeah - sounds like your setup works just fine. I'm also using two Titan X's as well. Was planning on switching out my third card for a GTX 950 Ti whenever they become available but not sure if that will make a difference. If the issue was my motherboard I would think my third card would not show up correctly in Device Manager so I'm completely baffled. For now, I just have to always remember to do that toggle off/on trick to get it to show up right as the PhysX card.

My configuration is stable, keeps after rebooting. More of interest is where are you expecting to see the impact of PhysX?
 

doubletake

Gawd
Joined
Apr 27, 2013
Messages
664
Haven't run a PhysX card alongside my SLI TItan X yet, but with my old SLI 780 + 750Ti setup, I never had a problem with the PhysX card not being detected, even with my sub-optimal 4-way z97 board with PLX chip (as opposed to your native x99 PCI-E lanes).
 

cybrnook

[H]ard|Gawd
Joined
Jan 14, 2013
Messages
1,202
Just want to throw out there, you do realize that unless you are on X99 or higher, or have PLX chips on board, when you add that third card, you are dropping the link speed to your primary GPU's..?

you are likely dropping from 8 x 8 to something like 8 x 4 x 4

Not sure how much PhysX rendering you are doing to make it worth a dedicated GPU, but if you are running anything recent, PhysX can surely be rendered on a Primary GPU, saving you some bandwidth.
 

wirk

Gawd
Joined
Sep 2, 2014
Messages
811
Just want to throw out there, you do realize that unless you are on X99 or higher, or have PLX chips on board, when you add that third card, you are dropping the link speed to your primary GPU's..? you are likely dropping from 8 x 8 to something like 8 x 4 x 4. Not sure how much PhysX rendering you are doing to make it worth a dedicated GPU, but if you are running anything recent, PhysX can surely be rendered on a Primary GPU, saving you some bandwidth.

There is zero impact of PCIe x8 or x4 on gaming performance, not even for PCIe 3.0 but also PCIe 2.0 which is half speed of 3.0.
 

cybrnook

[H]ard|Gawd
Joined
Jan 14, 2013
Messages
1,202
There is zero impact of PCIe x8 or x4 on gaming performance, not even for PCIe 3.0 but also PCIe 2.0 which is half speed of 3.0.

Makes sense...

I guess I don't even understand why motherboard manf's bother putting PCIe lane divider info in the documentation. Or why Chip manf bother to tell us how many lanes our chips have, or hell, why we even have PCIe Gen 3.0, guess none of it matters, let's go back to AGP.
 
Last edited:

bob616

Limp Gawd
Joined
Mar 30, 2015
Messages
166
Might be a setting in your BIOS I don't have that motherboard so I can't be specific but look for settings related to PCIe especially ones that scan for or are related to legacy hardware try changing them.
 

wirk

Gawd
Joined
Sep 2, 2014
Messages
811
Makes sense...
I guess I don't even understand why motherboard manf's bother putting PCIe lane divider info in the documentation. Or why Chip manf bother to tell us how many lanes our chips have, or hell, why we even have PCIe Gen 3.0, guess none of it matters, let's go back to AGP.

Increasing the bus speed is relatively simple so it's being done, remember the PCIe 4.0 is coming soon. But is also is very good for development since it makes possible for others component manufacturers to improve their performance, otherwise there is chicken and egg problem. In graphics cards we will have to see if DirectX 12 has higher demands on bus speed. It is known that Intel professional card for numerical computations aka Intel Phi can utilize fully the PCIe 3.0x16 bus capacity.
 

arestavo

[H]ard|Gawd
Joined
Mar 25, 2013
Messages
1,665
Makes sense...

I guess I don't even understand why motherboard manf's bother putting PCIe lane divider info in the documentation. Or why Chip manf bother to tell us how many lanes our chips have, or hell, why we even have PCIe Gen 3.0, guess none of it matters, let's go back to AGP.

Faugh! AGP? Try ISA! That's all we need :p

For the OP: I ran (3) GTX 580 Classifieds a couple years ago, and I could easily set 2-way SLI and then dedicate the unused 3rd card to PhysX. I would hazard a guess that Nvidia's drivers haven't regressed that much and so will still let you do that.
 
Joined
Nov 15, 2006
Messages
30
Just want to throw this out there, you do realize that OP IS on X99? "my motherboard somehow (a Gigabyte GA-X99-UD3P)"

l o l

Right. The lanes run at 16x/16x/8x.

It is interesting to hear others aren't having this problem. I guess I will double check the BIOS. (I tried a few options in there before starting this thread, but nothing changed.)
 

wirk

Gawd
Joined
Sep 2, 2014
Messages
811
It occurs to me that the problem might be in the types of cards used. If all cards are identical the system is confused at bootup since it is not expecting that one card should be PhysX, it is rather SLI or separate cards. If the cards are different, the distinction is clear since they can not be all in SLI. That would explain why I have no problems with 2xTiX+970.
 

doubletake

Gawd
Joined
Apr 27, 2013
Messages
664
ehhhhh, I don't see how that relates in any way to OP's problem. He's obviously not using 3x 750's as that's not even possible.
 
Joined
Nov 15, 2006
Messages
30
Well I scrutinized the BIOS again and can't find anything that would have any effect like this on the PCIe lanes. For now I've created a shortcut where if I double click it, it will instantly disable then enable the GTX 750 card in Device Manager. This will fix the issue until my next boot, as long as I remember to click on it of course.

(Adding the shortcut to my Startup folder doesn't work because my computer doesn't seem to like having a GPU shut off/shut on right at boot - my desktop switches to a dark screen until I restart!)
 
Joined
Nov 15, 2006
Messages
30
Also - I should elaborate that the two GPUs I'm using for SLI are EVGA Titan X's. It might be an important detail that it's EVGA since it doesn't seem like anyone else posting is having this issue - but I found a few people on the EVGA forums and elsewhere reporting this problem and so far they've all been using EVGA cards for SLI.
 

Dayaks

[H]F Junkie
Joined
Feb 22, 2012
Messages
8,288
The computer looks at which slot the cards are in so it can't really get "confused". Brand specific is interesting. You could always try flashing the BiOs of the cards are ref.
 

jolli

Gawd
Joined
Dec 17, 2010
Messages
784
I'm running two 970's in SLI with a 750 Ti for PhysX without issue. Drivers automatically default PhysX to the 750 Ti every time I reboot. Prior to the 970's, I ran 780's in a similar setup also without issue.

Board is an Asus Z97 Sabertooth Mark 1. Cards are Gigabyte 970 G1 Gamings. The 750 Ti is a MSI dual fan low profile model. The 970's are each running at PCIE 3.0 8x, and the 750 Ti is running PCIE 2.0 4x.
 
Joined
Nov 15, 2006
Messages
30
So far it seems anyone not reporting trouble is using two non-EVGA cards for SLI. I would be curious to know if anyone with EVGA cards in SLI and a third card for PhysX can boot up without this issue.

Whoever makes the PhysX card seems to be irrelevant to the problem. I was using an ASUS GTX 750 which I had been planning to upgrade. Today I switched my PhysX card out for a Gigabyte GTX 970. Unfortunately the 970 is not being recognized until I do one of the previously mentioned tricks to enable it.
 

jolli

Gawd
Joined
Dec 17, 2010
Messages
784
So far it seems anyone not reporting trouble is using two non-EVGA cards for SLI. I would be curious to know if anyone with EVGA cards in SLI and a third card for PhysX can boot up without this issue.

Whoever makes the PhysX card seems to be irrelevant to the problem. I was using an ASUS GTX 750 which I had been planning to upgrade. Today I switched my PhysX card out for a Gigabyte GTX 970. Unfortunately the 970 is not being recognized until I do one of the previously mentioned tricks to enable it.

I'm not sure how relevant it is, but the two 780's I ran were both EVGA SC models and they had no issues with a PhysX card.

Perhaps it is inherent to the 9 series? I'd post something on the EVGA forum, see if they can get a bios made for you.
 
Joined
Nov 15, 2006
Messages
30
Well I just installed Windows 10 on a second partition on my machine. I can now dual boot in either 7 or 10, and I have confirmed this issue does not exist on 10. So that tells me this has to be a driver issue.
 

Dan_D

Extremely [H]
Joined
Feb 9, 2002
Messages
57,409
Just want to throw out there, you do realize that unless you are on X99 or higher, or have PLX chips on board, when you add that third card, you are dropping the link speed to your primary GPU's..?

you are likely dropping from 8 x 8 to something like 8 x 4 x 4

Not sure how much PhysX rendering you are doing to make it worth a dedicated GPU, but if you are running anything recent, PhysX can surely be rendered on a Primary GPU, saving you some bandwidth.

Nvidia doesn't certify SLI on slots with fewer than eight lanes.
 

zaniix

Gawd
Joined
Nov 4, 2011
Messages
895
Nvidia doesn't certify SLI on slots with fewer than eight lanes.

He said in the OP that he is running a " Gigabyte GA-X99-UD3P" so running 8x/8x/4x for 2 way + PhysX should work.

I do agree I don't see the point, but to each his or her own.
 

Dan_D

Extremely [H]
Joined
Feb 9, 2002
Messages
57,409
He said in the OP that he is running a " Gigabyte GA-X99-UD3P" so running 8x/8x/4x for 2 way + PhysX should work.

I do agree I don't see the point, but to each his or her own.

For some reason I thought we were talking about 3-Way SLI.
 

ThE_MarD

n00b
Joined
Aug 26, 2015
Messages
22
Heyyo,

Faugh! AGP? Try ISA! That's all we need :p

For the OP: I ran (3) GTX 580 Classifieds a couple years ago, and I could easily set 2-way SLI and then dedicate the unused 3rd card to PhysX. I would hazard a guess that Nvidia's drivers haven't regressed that much and so will still let you do that.
Pfft, I have a 3D Labs Wildcat "AGP-PRO" GPU sitting in my closet. You're jelly, I can tell. :)



So far it seems anyone not reporting trouble is using two non-EVGA cards for SLI. I would be curious to know if anyone with EVGA cards in SLI and a third card for PhysX can boot up without this issue.

Whoever makes the PhysX card seems to be irrelevant to the problem. I was using an ASUS GTX 750 which I had been planning to upgrade. Today I switched my PhysX card out for a Gigabyte GTX 970. Unfortunately the 970 is not being recognized until I do one of the previously mentioned tricks to enable it.
Eh, I'd probably also submit a support ticket with Gigabyte on this one... I bet it's the motherboard maybe doing something wonky. Lots of BIOS updates even state stuff like "improved VGA compatibility" and such, so there could be a compatibility issue that your motherboard keeps running into on boot.

Tbh though? I don't think a GTX 750 has enough compute power compared to just using your regular GPUs in SLI with PhysX set to auto.
 

bigdogchris

Fully [H]
Joined
Feb 19, 2008
Messages
18,264
Just want to throw out there, you do realize that unless you are on X99 or higher, or have PLX chips on board, when you add that third card, you are dropping the link speed to your primary GPU's..?

you are likely dropping from 8 x 8 to something like 8 x 4 x 4

Not sure how much PhysX rendering you are doing to make it worth a dedicated GPU, but if you are running anything recent, PhysX can surely be rendered on a Primary GPU, saving you some bandwidth.
SLI requires minimal 8x8, and you are right, 3 GPU's would drop the system to 8x4x4 without the right board. The driver probably just disables PhysX to ensure the SLI is stable.
 
Top