Question inregards to max sli with same card phsyx and phsyx calculation

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07-20-2010, 12:12 PM
LiquidClocked98

Question inregards to max sli with same card phsyx and phsyx calculation

I've been looking a while back maybe 3-4 months ago, i might have saved the link somewhere, but i'd have to look for it. Basically i believe there was a guy who claimed to have not so good performance with 3-way sli or something like that and he was i think trying to do 2 way sli with 3 gtx 280/285's and 1 for dedicated phsyx. details are vague right now.

However he managed to do something and enable 2 way sli with phsyx same card and it ended up giving some serious fps, as opposed to tri-sli i believe. I think by replacing the tri-sli bridge or something like that.

Now i use to have 3 gtx 280's in tri sli and had phsyx enabled with them and i remember testing games such as mirrors edge and i would be baffled at the results i would be getting and results review sites would get. First of all gtx 280 tri sli with mirrors edge(in my tests) results in a color disorientation with flickering right from the start, you have to adjust the selected sli rendering optimization in nvapps.xml second of all i have not been seeing any SLI INCREASE PERIOD, not like these review sites we're stating.

Also enabling phsyx and disabling phsyx provided absolutely no frame increase as well, the only thing it did was just add destructive particles and flags and such. I read reviews back then stating that dedicated phsyx generates results but i've yet to see it(in terms of fps increase). This was a while ago, so my questions if anybody might know.

Say for example you get 4 gtx 480's and add a 5th gtx 480, can it be possible to make it a dedicated phsyx some how,if not i'm guessing the least alternative would be the gtx 470 acting as a dedicated phsyx

Second of all how does a dedicated phsyx work with say the other cards, do the 4 gtx 480's just not do any phsyx calculations at all?

I'm assuming here 4 gtx 480's with phsyx enabled the calculations splits up to each card, now if we have a dedicated phsyx, does 1 card solely calculate it and if so do the other cards continue to split the load as well.

example 4 cards 25% each add a dedicated phsyx add another 100% and thus when a game requires it splits up the load 4 gtx 480 12.5% each and 50% for the dedicated phsyx to calculate on the screen. Thus resulting in a fps increase since more rendering is being done instead of phsyx calculations

Thanks for reading.

EDIT: scratch the last tidbit in regards to the 25% of gtx 480 vs a dedicated gtx 470, got a little carried await with all the numbers. Bottom line question, if its possible to run a 5th gtx 480 as dedicated and how phsyx with 4-way sli or 3way sli works as opposed to a dedicated phsyx with 4-way sli or 3way sli, in terms of splitting up the calculation load.
07-20-2010, 05:56 PM
LiquidClocked98

Here i found it

http://www.evga.com/forumsarchive/pr...sp?m=100937833

This is what i was talking about check the post by

chizow

Quote:

Yes, you still get PhysX acceleration in SLI, but PhysX can only run on one of the GPUs. SLI on the other hand uses AFR which load balances rendering across both GPUs. The problem is, if PhysX is taking some of the processing time of one of the GPUs, it also reduces the mirrored amount on the 2nd GPU for SLI.

So for example, if you have PhysX consuming 25% of GPU1, that leaves 75% of both GPUx2, so maybe 150% optimally in SLI. If the game only scales to ~150% even without PhysX, you would most likely not notice the difference in FPS overall. If you start increasing the amount dedicated to PhysX, you start reducing the benefit of SLI. Once you eclipse the 50% point for PhysX, you're better off just running them independently, giving a full 100% dedicated to each.

The problem with Batman however is that PhysX on High is very stressful and will use significant GPU resources, probably 50% or more. Its also shown that on High setting, frame rates will generally be limited by your level of PhysX acceleration. So the faster your PhysX processing, the more FPS you'll get before you're GPU limited (similar to a CPU bottleneck).

Here's a pretty good compilation of results for Batman with a bunch of configurations. I also found the game runs better and smoother with SLI disabled, 1 GTX 280 for 3D and 1 GTX 280 for PhysX. Not everyone saw that with 2-way SLI, and there's definitely benefits from SLI + dedicated PhysX.

Now what i was wondering exactly is how phsyx dose balancing, phsyx is just an API gimmick by nvidia, all it really is, is nvidia paying dev's to use there preferred api which nvidia personally tunes its cards to optimize better.

The question though is how the balancing exactly works, what i'm trying to find out. If each card balanced everything accordingly then it wouldn't be a problem, but here's the situation in the link i posted it shows first of all some how he managed to get 2 gtx 280's to run instead of SLI as a dedicated phsyx, which is the first thing i'm wondering, how is that possible, because i was never given an option to have anything set as a dedicated phsyx i only had an option for SLI(something like this could then make enabling 4 way gtx 480's + 5th gtx 480 for phsyx possible)

Second of all he states that percentage is being lost from the other card when phsyx is being enabled because he claims phsyx only works on 1 CARD even if your running sli(i'm assuming the same would apply to 3/4 way), when phsyx is enabled it allocates 25%(supposedly) to the first card and the remainder percentage of the cards is being rendered useless cause sli works in mirror, for example if you ran 4 gtx 480's your losing 18.75%(75 out of 400) from your total 4-way gtx 480 sli graphic power(not sure about dual gpu cards). What i'm trying to find out is actual fact in regards to how the balancing literally works, if indeed the first card only runs a certain amount of phsyx and renders the other cards useless. That would explain why a dedicated phsyx card gives more performance in a game that requires phsyx and also in scenarios with multi-gpu, second of all, if it is true we're talking about 25%-18.75% performance loss from sli to quad. Which i don't know about you sounds serious to me.

Anyways i hope you guys are seeing what i'm getting at

EDIT: i don't think it's the right link i was talking about, because i seen one where a guy managed to get 2 gtx 280's in sli and another gtx 280 as dedicated phsyx, which i also don't know how he managed to do, nether the less i believe the point is similar.

EDIT2: Another article http://supercomputerinfo.com/a/Video...-Ge/10956.html

Quote:

At a resolution of 1600x1200 the results were close to the same. I found it interesting that a pair of GeForce GTX 280 video cards in SLI with a GeForce 9600 GT being used for PhysX performed better than a set of GeForce GTX 280 video cards in 3-way SLI.
07-20-2010, 08:12 PM
Carfax

Quote:

Originally Posted by LiquidClocked98

Say for example you get 4 gtx 480's and add a 5th gtx 480, can it be possible to make it a dedicated phsyx some how,if not i'm guessing the least alternative would be the gtx 470 acting as a dedicated phsyx

Provided you have enough PCI-E slots, you could set the 4 GTX 480s to quad SLi, and then use the remainder for dedicated PhysX yes.

I don't think any motherboard supports that many GPUs though.

Quote:

Second of all how does a dedicated phsyx work with say the other cards, do the 4 gtx 480's just not do any phsyx calculations at all?

In your theoretical set up, if you have your 5th 480 tagged for dedicated PhysX, then no, the other 4 GTX 480s would not do any PhysX calculations.

They would perform rendering only.

Quote:

I'm assuming here 4 gtx 480's with phsyx enabled the calculations splits up to each card, now if we have a dedicated phsyx, does 1 card solely calculate it and if so do the other cards continue to split the load as well

As I said above, the card that is tagged for dedicated PhysX will perform PhysX calculations only, leaving the other GPUs for rendering in SLi mode.

Quote:

Bottom line question, if its possible to run a 5th gtx 480 as dedicated and how phsyx with 4-way sli or 3way sli works as opposed to a dedicated phsyx with 4-way sli or 3way sli, in terms of splitting up the calculation load.

Is it possible to run a 5th GTX 480 as dedicated PhysX? Sure it is, but as I said above, I don't think any consumer grade motherboard supports 5 GPUs.

Also, for PhysX stuff, dedicated PhysX is almost always faster than SLi.

If you have a 3 or 4 way SLi config and enable PhysX, then the PhysX calculations will be performed on only ONE of those GPUs, in addition to rendering tasks, because PhysX is NOT multithreaded.

SLi + dedicated PhysX is going to be faster than Tri SLi for PhysX titles
Tri SLi + dedicated PhysX is going to be faster than Quad SLi for PhysX titles

Of course it all depends on the game you're playing. Some PhysX games don't require much resources (Metro 2033), but others like Batman AA, and the upcoming Mafia 2 do.
07-20-2010, 08:15 PM
Carfax

Quote:

Originally Posted by LiquidClocked98

EDIT: i don't think it's the right link i was talking about, because i seen one where a guy managed to get 2 gtx 280's in sli and another gtx 280 as dedicated phsyx, which i also don't know how he managed to do, nether the less i believe the point is similar.

If his motherboard supports Tri SLi, then there's no reason why he couldn't use 2 GTX 280 in SLi, and another GTX 280 for dedicated PhysX.

My own motherboard supports Tri SLi, and I have 2 GTX 480s in SLi (coming Thursday) and a GTS 250 for dedicated PhysX.
07-20-2010, 08:41 PM
LiquidClocked98

I was referring to same video card phsyx, not just a different card, thats the option i never seen when i ran gtx 280 3 way sli. What i was really wondering about is how the balance works with SLI/3way/4way in terms of phsyx, does phsyx only work on 1 CARD? or is it split up, that's the main issue here. How does non dedicated phsyx split up the load.

EDIT: I've been reading around and, i've yet to see anybody confirm 3way sli with same card or 2 way sli with same card can do phsyx on the same non sli'd card. Also doing more research it seems, that enabling phsyx with out having a dedicated phsyx card actually results in wasted graphics power and if you want to run phsyx then you would indeed need to buy a dedicated card.

Thats why i'm trying to find out exactly how the balance is working with non dedicated phsyx 2 way 3way 4 way.

EDIT2: in your comment about sli+ dedicated phsyx will work better then tri sli. That is exactly my point and confirms what apparently i've getting at, that physx with out dedicated card, runs at a small percentage on only 1 gpu and thus rendering the same percentage on the other cards useless and wasted for no reason in terms of performance. Cause tri sli and 2 sli with dedicated phsyx offers no difference in computing power, the situation appears to be that phsyx with out dedicated pshyx neuters your performance when it shouldn't
07-20-2010, 09:14 PM
LiquidClocked98

http://www.nvidia.com/object/physx_faq.html

Quote:

How does PhysX work with SLI and multi-GPU configurations?
When two, three, or four matched GPUs are working in SLI, PhysX runs on one GPU, while graphics rendering runs on all GPUs. The NVIDIA drivers optimize the available resources across all GPUs to balance PhysX computation and graphics rendering. Therefore users can expect much higher frame rates and a better overall experience with SLI.

A new configuration that’s now possible with PhysX is 2 non-matched (heterogeneous) GPUs. In this configuration, one GPU renders graphics (typically the more powerful GPU) while the second GPU is completely dedicated to PhysX. By offloading PhysX to a dedicated GPU, users will experience smoother gaming.

Finally we can put the above two configurations all into 1 PC! This would be SLI plus a dedicated PhysX GPU. Similarly to the 2 heterogeneous GPU case, graphics rendering takes place in the GPUs now connected in SLI while the non-matched GPU is dedicated to PhysX computation.

Man i'm afraid i'm going to have to test this stuff myself and find out, cause the stuff there saying don't make sense. It seems to be a lie

There saying a game that if you run sli with phsyx enabled that one of the cards will dedicate itself completely to phsyx, which confirms what the guy from evga forum was saying, the only problem is and what i'm starting to recollect from another thread i can't find, is whether non dedicated phsyx actually run's at 100%, which i dont think it does, cause it doesnt add up to what people have been reporting

Heres another example

http://forums.guru3d.com/showthread.php?p=3540185

Quote:

Single 480 + 480 Physx: Min:42 Max: 126 Ave: 80
480 Sli: Min: 33 Max: 103 Ave: 67
480 Sli +280 Physx: Min: 64 Max: 166 Ave: 103

I think this appears to be the issue. notice SINGLE 480 and 480 dedicated as phsyx and 480 in SLI, both have the same computing power, but it appears what the evga forum member was saying is true a percentage is allocated to 1 card and the rest of the system wastes the percentage doing nothing.

EDIT: i did a percentage calculation with his 480 single + 480 dedicated against his 480 sli and the percentage loss comes to minimum: 22% max: 19% Average: 17%

So it seems to make to sense, would be good to confirm though.