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!)

 

[martcerv]

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

Have you tried running just 2 Titans, I have heard lots of reports of negative scaling with 3. For example RF2 I get ok rates with a single card and unplayable low fps in SLI trying every possible custom option in NV inspector as that is simply broken with SLI though the old ISI engine works great as in RF1 and GSC 2013.

Also AC is very CPU limited with lots of AI you will see your GPU loads very low with a full field and I will get the same min rates maxed out or min GFX setting with a full AI grid. An extra GPU will help when you are gpu limited but if the cpu is the bottleneck then its just going to hurt your min FPS most likely.

You can up the AA settings and max everything out but still this wont change the fact that your cpu is bottle-necking the entire system. My Titans also have custom firmware flashed and are fairly overclocked as is the CPU.

The latest build has given a good performance boost and supposedly the next build is even better. I also force some settings in NV inspector such as AF, which seems broken ingame at 16x being worse then 8x but forced in inspector or nv control panel af 16x works as it should. I still keep experimenting with AA as its never been quite right, if anything combined AA maxed on both gives the bes image but with some blurring due to FXAA. 8x SS forced I really dont know if it works and sparse grid in AC is very pixely for me for some reason so I cant use that.

 

[martcerv]

Looks like the next build will have some good performance optimizations going by this vid and specs listed of what it ran on.

Published on Mar 25, 2014

I got the chance to record some video footage by iPad showing Assetto Corsa on the new ACER B296HCL at 2560x1080: the video shows the new build that will be released on March 28th, with improved AI routines and collisions, improved lighting (more and sharpening contrast), new sky/clouds and some general optimization.

PC configuration:
Intel(R) Pentium(R) CPU G840 @ 2.80GHz 2.80 GHz (Celeron)
4GB RAM
nVidia Geforce GTX 680
video settings - mid/high settings
15 cars on track

 

[Billy Pilgrim]

The main thing is AC is quite CPU limited

(I'm new to this) What does "CPU limited" mean?

 

[Billy Pilgrim]

I recently upgraded to 8.1 Pro but when i was using Win 7 premium I had manually changed my CPU cores to unparked to reduce stuttering in some games..
.

Btw, any views on which is better: Windows 7 or 8 for a gaming pc?

 

[Stelios]

(I'm new to this) What does "CPU limited" mean?

It means that this game is using a lot of CPU power, so if you have a 600€ gfx card and a slow CPU the game will run badly.

 

[Billy Pilgrim]

It means that this game is using a lot of CPU power, so if you have a 600€ gfx card and a slow CPU the game will run badly.

Thanks, any idea what a fast enough CPU would be?

 

[Tim Meuris]

Btw, any views on which is better: Windows 7 or 8 for a gaming pc?

I heared 8.1 would be better but others contradicts and stay with 7

 

[Turk]

Thanks, any idea what a fast enough CPU would be?

It depends on what you want to achieve. If you want full grids of AI then you need a powerful CPU. When I have something like 20 cars on the track my i7 2600K starts to struggle.

It may also be the case that this will improve with time so it's hard to say at this stage because the games performance is due to improve today and again in two weeks, then again two weeks after that.

Many people seem to do just fine with a decent i5 processor.

 

[Martymcfly]

Btw, any views on which is better: Windows 7 or 8 for a gaming pc?

Go with windows 8.1 it has the latest DirectX 11.1 and in the future when Microsoft releases DirectX12 it should still be compatible with windows 8.1 unless they force us to buy windows 9 to get it....
There is a wide range of discussions on forums about this topic including reviews that clearly show that windows 8.1 has better CPU optimizations in several games. It would be cool if someone could do a little review to see if AC benefits from windows 8.1 over win 7.
Billy Once u tame that beast you will love 8.1, I am glad I upgraded from 7

 

[Leemstradamus]

I might dual boot it.

 

[gerard27]

the game is very poorly optimized for the time it takes the noob programmer

 

[Bokonon]

A considered and intelligent response, only slightly marred by that terrible 'merde' icon at the end. Can it be removed moderators? I mean completely? Either that or autoban anyone using it for a week or so Even a 'noob coder' could manage that...

 

[Stereo]

Also AC is very CPU limited with lots of AI you will see your GPU loads very low with a full field and I will get the same min rates maxed out or min GFX setting with a full AI grid. An extra GPU will help when you are gpu limited but if the cpu is the bottleneck then its just going to hurt your min FPS most likely.

It's hard to do diagnostics just based on the CPU/GPU usage but it seems like AC runs on 3 main threads - physics, graphics, audio - so if the CPU is limiting the graphics thread then there might be graphics settings that affect the bottleneck that way. I don't really know how much it has to communicate to the GPU each frame though, or what settings affect that - AA, resolution, etc. shouldn't matter much.

I do have a fairly slow CPU though (2.6GHz AMD Phenom II x6) so maybe those 3 threads are less equal on procs that can actually run a full grid at 60fps. Mine drops to about 30fps by the time I have 20+ cars on track at once.

 

[gerard27]

a longer explanation for blind fanboy would inutil, but you're on the right track

 

[gerard27]

It's hard to do diagnostics just based on the CPU/GPU usage but it seems like AC runs on 3 main threads - physics, graphics, audio - so if the CPU is limiting the graphics thread then there might be graphics settings that affect the bottleneck that way. I don't really know how much it has to communicate to the GPU each frame though, or what settings affect that - AA, resolution, etc. shouldn't matter much.

I do have a fairly slow CPU though (2.6GHz AMD Phenom II x6) so maybe those 3 threads are less equal on procs that can actually run a full grid at 60fps. Mine drops to about 30fps by the time I have 20+ cars on track at once.

you begin to understand the principle

 

[martcerv]

Lates build seems to be worse in SLI with other cars on track niw i get much the same fra es as with a single card. Running on my own with no apps on screen is ok but i think something is breaking sli with other cars on track.

I also found the on screen apps a huge fps killer or even just any txt on screen running single gpu or sli. This was with 0.8 havent tried 0.8.2 yet but didnt see anything about this. I did a comolete reinstall and full default nv profiles but getting worse performance now and lower cpu and gpu useage at the same time with a full field.

The beauty of beta or pre release each build is like a box of chocolate. Was running real good for me on 0.7.8 but now i need to figure out what is the main issue other then just on screen apps.

I added a post to my apps bug thread at the official forum showing some tests and fps hit in sli and single gou on my setup.

 

[Leemstradamus]

I concur all the same issues. I even get a FPS drop when the Delta times pop up after crossing the start finish line.

 

[martcerv]

The latest bugfix 0.8.2 has made a good step in the right direction again, looks like they fixed the text overlay issue as it has no impact on me even in SLI any more. The apps are also better but some have more impact then others but I am using the Dashmeter pro app now which gives me all I need with no performance impact.

One thing I experimented with is cube faces, having this at 6 is a bit of a fps hog setting it to 4 I dont see any difference and get a big performance boost. With everything else maxed except no motion blur and cube res med and 4 faces in the 12 car challenge races im getting 120-180fps and 24 cars at Nurburgring dropped to below 60 just after start then was 80-120 in traffic for 5 laps with the odd dip below 80 but quite rare. I am having the race position app on screen only for races as dashmeter only updates position at the end of each lap.

With cube res I can set this to high with 4 faces and it only costs maybe 5 to 10 frames on the min and a bit more on the max but really doesnt look that much better so Im just keeping it at medium.

I have smoke on ultra putting this back to high or norm will avoid any slowdown at the start of a race and again Ultra doesnt look that much better so not much point using it in large fields.

I am still experimenting with forcing different AA settings and also force 16xAF in driver as the in game 16x never seemed to work properly. Forcing AA also needs AA ingame and Im really not having much luck improving AA quality but this has always been a bit of an issue in AC.

 

[Leemstradamus]

I've never been able to see AF work through the driver for me also dash meter pro is amazing! I wish it didn't take 2 to 3 laps to update fuel. I kind of like not having my position updated to the end the lap. it's like looking at the pit wall for information.