To use SLI or not to use SLI, that is the question

[Billy Pilgrim]

Sorry about the predictable Shakespeare parody title for this thread. Couldn't resist.

I'm about to start building a pc, specifically for racing sims, and especially for AC and pCARS.

I'll be using a triple-monitor setup.

Please tell me, what is better for running Assetto Corsa: one GPU or two? I know that some sims run better with one GPU rather than two, but what about AC?

I'm hesitating between getting a GTX 780ti or two 780s

If you know anything about pCARS regarding SLI, I'm all ears.

(First post here - yeeah!)

 

[Leemstradamus]

First welcome to the community! Next I run SLI and assetto corsa with no problems with it. Haven't run pcars for some time but it needs custom profiles.

 

[Paul Luck]

I run triples with a single R9 290 virtually maxed out. Don't see the point of wasting money on SLI or XFire when building a new rig. Maybe if you have older card which you want to add a 2nd one too, but that's assuming SLI XFire actually works with the game which is always a big IF.

 

[Bokonon]

SLI runs very well for me with two 460's @1920x1080. Don't run Pcars so can't tell you about that. What I will say is that having run an SLI setup for, well must be close to 2 years now is that it is great for the most part but it will let you down at some point. Cliffs of Dover and Rome II are two cases in point for me. If I had the choice of those two setups, I'd tend towards getting the better card in the knowledge that I could add one at a later point in time for a much reduced price. I bought my 460 for a shade over £200 when it first came out, and the second for about £115 less than 12 months later, it worked for me anyway. Having said that I'm not gaming on three screens. One guy I know over at Sim HQ is running two titans for his triple screen setup, his rig cost more than my car! So it goes.....

 

[Leemstradamus]

I've been running SLI since 2007 and I have very rarely been disappointed! Rome II is one of the few that I am disappointed with. But that seems to be all CA's fault on that one. I haven't run it in months because of it. Now the thing is SLI will give you extra performance but a lot of people try to get more power and save money. I do the opposite, blow money and get way more power! When you SLI top end cards, nothing compares. That's why you do it, for ultimate performance!

 

[Billy Pilgrim]

I've been running SLI since 2007 and I have very rarely been disappointed!.....

Thanks for your reply, Saleem
Have you got any experience with other race sims running SLI?
In your post further up, re pcars, you mention custom profiles. I'm new to pc gaming - what are custom profiles?
And thanks for the welcome. It's nice to be here!

 

[Billy Pilgrim]

SLI runs very well for me with two 460's @1920x1080......

Thanks, Bokonon, for your reply "So it goes..." Great!
Indeed, I've also been considering the option you suggest (to buy one now, and one later)., and that may be the solution. But the demands of three screens mean I'm really looking for a lot of GPU power right from the start.

I'd love to know about your experience with any other racesims and using SLI.

 

[martcerv]

I use SLI with AC and 2 Titans works great, I noticed a small issue with the overlay APP's having a negative effect on SLI. It still ran OK with the apps but is really good with no apps on screen since I started using dashmeter pro for the in car extra data info. This will likely be addressed in a future firmware update but even with apps I get close to 60p min rate just gets another 20+ frames on the min end with them disabled at the moment.

I only have a single 2560x1440 screen but can max it out with a full field of AI and get solid frames above my refresh rate, turn a couple settings down and it can get 100+ with lots of other cars and single car 250+ with near max settings.

I dont have Pcars so cant say, RF2 doesnt work at all with SLI atm I get less then half the frames in SLI compared to a single card. RF1 I think I could run 4k tri screens fully maxed as I can run the most insane AA settings and still get crazy frames at my res the same with GSC 2013.

A pair of 780ti will be good for most sims, I got titans for the double precision and cuda but if its just for gaming the 780's are even better.

 

[Billy Pilgrim]

I use SLI with AC and 2 Titans works great, I noticed a small issue with the overlay APP's having a negative effect on SLI. It still ran OK with the apps but is really good with no apps on screen since I started using dashmeter pro for the in car extra data info. This will likely be addressed in a future firmware update but even with apps I get close to 60p min rate just gets another 20+ frames on the min end with them disabled at the moment.

I only have a single 2560x1440 screen but can max it out with a full field of AI and get solid frames above my refresh rate, turn a couple settings down and it can get 100+ with lots of other cars and single car 250+ with near max settings.

I dont have Pcars so cant say, RF2 doesnt work at all with SLI atm I get less then half the frames in SLI compared to a single card. RF1 I think I could run 4k tri screens fully maxed as I can run the most insane AA settings and still get crazy frames at my res the same with GSC 2013.

A pair of 780ti will be good for most sims, I got titans for the double precision and cuda but if its just for gaming the 780's are even better.

Martcerv, thanks for your reply. Great!
I wanted to know about GSC 2013 and SLI. So you get great framerates in GSC 2013 using SLI? That right?

 

[martcerv]

Yes GSC 2013 works very well with SLI maxed out with regular ingame AI and all works great though the game itself is only single threaded so its CPU bound with lots of AI. I think you could likely max everything out with a single Titan but you can even run 64x SLI AA with 16x SS and it has zero effect on frame rates due to it being CPU bound.

I just tried it again and checked the OSD and actually got better frames earlier but think I had HT off then which benefits single threaded apps, actually benefits anything running 3 or less threads on my i7 2700@4.8ghz.

Getting 84fps at 2560x1440 maxed back of grid at Interlagos in mini's and 260fps on my own. GPU load with AI drops quite a bit as the CPU single thread is the bottleneck with GPU load even at those settings down quite low with lots of AI. I tool some screen grabs but for some reason cant post them here, I will reboot and turn off HT to see what the performance diffrence is.

 

[martcerv]

Ok tried HT off and not much difference but then I remembered the old +fullproc command line for RF1 so I added this and now magically I am getting 250fps back of grid with 64xaa and 16xSS in GSC 2013 which is exactly the same as I am getting on my own.

Not sure exactly what that does but always seemed to give me a boost in RF1, it did its magic even in GSC 2013 with the GPU usage at 95-98% on both GPU's.

Couldn't upload pics here so posted some screens with afterburner OSD in GSC2013 at Interlagos with max grid 24 or 25 cars I cant remember. I labeled the screens correctly I hope but if you see 8 CPU's that HT on and 4 is HT off. I also labelled the ones taken with the +fullproc command line. You can see the difference in GPU load with these, I get the same FPS pretty much any GFX settings so may as well max everything including AA if its much the same only GPU load drops with lower AA settings.

https://www.mediafire.com/?n411mqcqp6esgin

Tried the normal SLI rendering mode forcing AFR2 with 16xQC AA and 8x SS with a full field at another track and getting over 300 fps with this at all times in traffic. The + full proc actually makes it use more cores as before it only used one thread at 100% but now its loads up all cores with HT off and 2 of them are close to 100% so thats why I am getting much more performance with that command line. Will need to try it on AC

 

[martcerv]

Dont know how to force a command line to ACS.exe it doesnt work in the same way as a regular shortcut as its launched via the launcher.

I tried to see how nuts you can go with AA in GSC 2013 and here are a few more screens the one at over 300fps is the regular 16x QS 8x ss but the other 3 I maxed out the supersampling to 8x sparse sampling and it looks amazingly clean yet still runs at 150+ in car back of grid and close to 100 with a tv cam looking at the full field. This super sampling mode brings most modern game engine to its knees but the old ISI engine is no match for a pair of titans.

It doesnt look as pretty as AC and id love to try pcars but cant get that atm but I love a very sharp image thanks to extreme AA if it can handle it and GSC should have no issues at nearly any res at any settings with a pair of 780TI or Titans I think.

https://www.mediafire.com/?32yba567sjyp9u6

I really hadnt played much GSC lately and only a little since getting my second GFX card, using more regular GFX settings 8x aa and 8xSS full field in a race Im getting 250-700fps lol.

 

[Billy Pilgrim]

Thank you, martcerv. Great! Checked out your screenshots. Very impressive framerates

 

[Leemstradamus]

Great info @martcerv , I have the same overlay bug with assetto corsa.

Custom profiles are a little advanced so don't feel bad about not hearing about them yet. basically you would have download Nvidia inspector. Once it's launched you have to click a button (I'll go into better detail later) and you get something like Nvidia control panel but much more advanced. In there you can create profiles for all your games and tell it how to Handel SLI and anything else.

 

[Pedro Cunha]

I use SLI with AC and 2 Titans works great, I noticed a small issue with the overlay APP's having a negative effect on SLI. It still ran OK with the apps but is really good with no apps on screen since I started using dashmeter pro for the in car extra data info. This will likely be addressed in a future firmware update but even with apps I get close to 60p min rate just gets another 20+ frames on the min end with them disabled at the moment.

I only have a single 2560x1440 screen but can max it out with a full field of AI and get solid frames above my refresh rate, turn a couple settings down and it can get 100+ with lots of other cars and single car 250+ with near max settings.

I dont have Pcars so cant say, RF2 doesnt work at all with SLI atm I get less then half the frames in SLI compared to a single card. RF1 I think I could run 4k tri screens fully maxed as I can run the most insane AA settings and still get crazy frames at my res the same with GSC 2013.

A pair of 780ti will be good for most sims, I got titans for the double precision and cuda but if its just for gaming the 780's are even better.

What is you refresh rate?
You can't run the game with full AI maxed out above 60fps with those two titans, Sir!!!!
PS: Not even run Pcars under same circumstances...

 

[Leemstradamus]

Yes you can with two titans

 

[Billy Pilgrim]

What is you refresh rate?
You can't run the game with full AI maxed out above 60fps with those two titans, Sir!!!!
PS: Not even run Pcars under same circumstances...

martcerv has the screenshots to prove it

 

[Pedro Cunha]

Yes you can with two titans

Do you have two titans?
I have 3 titans now and still can't stay above 60fps with full grid maxed out

 

[Pedro Cunha]

martcerv has the screenshots to prove it

you can get 60+, but you will still drop from 60 with full grid maxed out game

 

[Leemstradamus]

Do you have two titans?
I have 3 titans now and still can't stay above 60fps with full grid maxed out

I have two 680's and get better performance than you, which shouldn't happen! Your system has an issue. We have been through this. If you now have three then you should still get even larger performance. Something is wrong with your system.

Saying that the game is broken, when everyone else says contrary should let you know to check out what else could be wrong.