Performance Mystery

Hi guys,

I have been trying to get to the bottom of why I have poor performance with full grids. Tonite I just sat on the grid with the render stats up to try and see what I could find.

My Rig has been upgraded with GTX 1080 and i5 4670K. I am running oculus.

Here are my findings:

Start of race with 11 AI

Race start is 45 fps

CPU usage of about 70%
Physics about 25-30%
FMOD DSP 7%
FMOD Usage about 15%

As the cars drive off the fps goes up, however while the cars are out of sight the fps still drops at various points around the track (Magione)

Each time the cars go past me on the grid the fps will drop progressively lower as more of the cars go past.

I have no idea what to do to improve performance as I have tried to lower settings even to the lowest gfx settings but the drops are pretty reproduceable.

Any ideas?

I would buy a new processor if I could get confirmation that this is not a performance issue with the current way physics works as I never had issues with larger grids in previous builds.

 

I manage to run 40 cars, on spa at ~60 fps with mild dips down to the mid 55's.
Normal tracks with full grids, without expanded pits, average 80-100+ fps. I manage this by turning reflection frequency down to static.

Judging by the options in the AC config file assetto_corsa.ini found here: \SteamLibrary\SteamApps\common\assettocorsa\system\cfg

I suspect grid size is impacted by the number of threads a CPU features. As well as your settings / configuration of the game. Someone else can probably make a better, more informed suggestion/comment...But i'd think more threads might indeed help your situation (a new i7 etc. CPU). At the very minimum i'd go and turn reflection frequency down to static, and try again with your current setup.

 

The big CPU use spike is collision calculations, in order to find calculations between a grid of 20 cars, you have to compare 190 pairs of cars to see if they're colliding. The bigger the grid the more this dominates, because unlike most of the physics calculations it's growing as the square of the number of cars on track - 20 cars is 4 times as much CPU load as 10 cars, 30 cars is 9 times as much CPU load. At a certain distance from the player this gets simplified so once the grid spreads out it's not as bad.

 

It would help to state what FPS you're actually getting, low doesn't really help.
What settings are you using in-game? Is everything pumped to the max?

Have you tried renaming the docs folder? After one update I was getting poor performance till I renamed it and the next race I had 100 fps as previously I had 45.
Probably a good idea to upload your log files, maybe it's a mod you're running that's causing it?

In single screen run the benchmark and post up your report.

 

I'm away from my machine right now but I'll get back with benchmarks. I've actually run them multiple times, but I can't seem to isolate anything that looked weird or helped.

I have dumped the Assetto Corsa documents folder.

I have uninstalled all apps

I have run with static and no reflections

Additionally I have set the sound to normal just in case FMOD was taking more CPU cycles even though I had no problem with sound.

Is the theory that my CPU in render stats should be at 100% when it has peaked or is it an in-game measure. If I try to monitor the CPU on my system it seems to reflect the same as the Assetto render stats usage. Which in theory would indicate that the CPU is not bottlenecking anything...

 

In the main steam window, have you gone into library/right clicked on Assetto Corsa, selected the Local Files tab, and ran "VERIFY INTEGRITY OF GAME CACHE" ?

 

Usually is safe to uninstall any kind of App in Assetto Corsa first when you experience bad fps.

 

At the moment VR runs like crap on pretty much any system so it would make sense to eliminate that from the equation and see how things run under more normal circumstances. From what I've read above and elsewhere I'm not sure that the problems you describe are much different to everyone else running VR.

We know that the physics and AI of AC put far higher demands on the CPU than most other games. As far as I'm aware, the main overhead with VR - the scene having to be created independently for each eye - is also something that puts more strain on the CPU rather than the GPU. The result being that AI+VR kills performance.

I'm (still) waiting for my 1080, but even paired with a 6700k I've got reservations about how well it will cope with a lot of AI opponents.

 

Your i5 processor has four cores with no threading. In AC Core #1 is dedicated to rendering the screen output, the other three cores are dedicated to running physics on the cars. Each car has it's own physics thread. Cars add a lot of work to the cpu.

The "cpu percentage" indicator tells you how hard the overall processor is working. If one core is working at 100% and the other cores aren't working at all then the cpu percentage would show 25%. A core can't pass work to another core if the programing doesn't allow it. Most games don't utilize multi core processing very well. AC actually does this pretty well as it utilizes one core for rendering and the others for the physics calculations.

The difference between an i5 processor and an i7 processor is multi-threading. With multi threading the cpu essentially treats a core as though it were 2 cores if the software allows it. With AC this doesn't impact Core #1 which is dedicated to rendering but it does double the number of program streams which can be handled by the other three cores. This means an i7 has 6 threads going while the i5 has 3 threads and increase in the number of cars that can be calculated. The clock frequency on the cpu determines how many calculations can be processed in a unit of time so a faster clock helps both the rendering and physics units.

While I haven't heard Stephano state directly I expect that the render waits to have information on each car completed before it produces another frame. This means when your cpu can't get all it's work done the frame rate begins to drop. Apparently collision calculations add work. This explains why crowded first corners really slow the unit.

With my i7 6700 OC at 4.8 GHz running on my gtx1080 OC at 2000MHz, I can sustain 90fps on a 16 car grid with 1.5 X pixel density, AA2X, AF 16X, PP on default, and other settings on ultra. I get a decent display on my Rift. If I start taking the cars up from 16 I start losing fps particularly at the start.

My interpretation of this information is that even with an OC i7 6700 I am still cpu limited. The gtx 1080 can easily keep up with the cpu when it can provides the frames as it does with up to 16 cars. The cpu can't get all the calculations done when there are more than 16 cars when they are banging together in the first corner.

 

As I reported above, I can sustain 90 fps on my i7 6700 OC 4.8GHz with optimized settings on quality for a field of 16 in an AI race. I start to lose fps if I go above that. A field of 20 is pretty good, a field of 24 is pretty marginal.

 

Probably the first reasoning for the terrible racing performance (on my machine) of AC - thank you.
I have, however, to ask, why does this not appear with any other racing game? Shouldn't the collision calculation be streamlined a bit, aiding the performance / larger grids.

Best regards,
Brett

 

Those of us who bought in to AC during early access have watched the AI get better and less CPU heavy with time. The first AI release was basically unworkable above 12 cars.

Clearly there is still plenty of optimizing to do, but since every patch brings major updates to the AI and since I can quite easily race 23 AI as long as I don't mind frame rates dropping slightly below 60 on the grid, I'm personally fine with it.

More importantly, for the consoles they have to work with a lot less Cpu power than my i7 6700k, so I am very curious how that plays. I'm expecting those optimizations to benefit PC users too.

Since I already preordered AC for the PS4 (my console rig doesn't get enough play at the moment and GT Sport won't be out for ages) I am looking forward to comparing the AI between the PC and PS4.

 

If this is true then we have a problem.

An i7 with 1080 not being able to run a full grids asks the question of what type of machine would you actually need to run it.

In answer to some of the other responses: I get the way Assetto uses cores but in Windows it shows each core getting utilised at the same amount and I get drops even with 70% on each core.

This doesn't make sense to me. I'm going to run some benchmarks for you guys but I think this is clearly broken in some way.

When we break down the areas that it could be I see no full loading for memory, CPU or GPU.

I have uninstalled all third party apps.
Verified integrity.

To me it just doesn't make sense that right now we need something more beefy then an i7 6700 with 1080 to make things better.

@lordkunos @acsupport @help!

 

The worst offender settings are reflections and mirrors. Have you tried turning these down? Have you tried running AC with post processing disabled to see what that does for frame rates?

 

I usually drop Smoke to Low, lower reflection to Medium. Usually this is enough.
But if that doesn't help, Shadows to High.
I also use Natural Mod PP, it helps with performance quite a bit.
i7, 980, 4K

EDIT: Time of the day matters too, evening hours are the worst due to shadows and god rays.

 

Take a really good, hard look at how your hardware is configured.
Things like the OS drive on a slow controller or the videocard in less than optimal slot etc... can be the source of your grief.
With your system specs, you should be absolutely 'flying' through AC.

 

The latest patches after 1.7 seem to have hurt performance somewhat in VR. I was getting a very solid 90fps even with AI, but the latest patches have made my game stutter at certain sections of the track even with no AI. There's definitely something weird that needs to be fixed.

 

Just for the record guys.

I have tried with static reflections and mirrors low. I don't run PP due to not getting 90fps always without.

I have dumped my Assetto documents folder but with no luck.

I know my system in theory should fly. What I'm looking for is somebody that is able to say "yes I can run 90fps with a normal grid with medium settings" and then state their specs.

So far even beast machines cannot, so I want to know why and what do we need to do it as it seems unlikely that Assetto is outdoing beast machines

 

Take a look here: https://www.assettocorsa.net/forum/index.php?threads/benchmark-results-food-for-thought.28103/

maybe someone can help. We have some users claiming they can "run 90fps with a normal grid with medium settings". If you check LurdKunos videos he gets well over 200fps (not with 24 AI)

 

Should you also consider VR support isn't quite finished?
Performance wise until it's implemented you might find limitations even with the fastest systems.

i7 4930k @ 4.2ghz with a R9 290x and I can't run PP or reflections but I can run 1.5 pixel density. 4x AA and 16x AF. World detail to medium, shadow on high.
Normal smoke showing in mirrors, mirror detail on high. 12 AI cars and I get a solid 90 fps.