CPU Bottle-necking in iRacing ( and Sims in general )

[groove200]

Apologies in Advance...this may be long

A bit of context , picked up a Valve Index last week and spent an inordinate amount of time messing with settings trying to get a good experience. It was suggested my CPU could be bottle necking my experience so I set about today to try and find evidence of that and learn about CPU, cores. threads etc

I can drop some money into this to fix my problem , but before i do that ( CPU,MB,Mem) I needed to be sure id see enough benefit. I've found out that the amount of cores really doesn't matter THAT much in iRacing , but core speed probably more important ( stop me if im wrong )

Somebody advised id see a core maxed out and that was my problem , but I dont see that in my graphs ( they all look kind of equal ) . But reading up im not sure threads are pinned to a core , but instead are time sliced across all , so it wouldn't maybe show up like that anyway ?

So ive spent the morning with perfmon , proc mon , proc explorer , resource monitor and MSi afterburner trying to get my head round what actually is going on. I decided to do all these tests on my Samsung 49" 32:9 monitor so as not to bring the complexities of VR into it just yet. I figure if I can understand what is going on in this scenario I can better what is going on in VR.

Current specs of my Rig



Im no PC Overclocking Guru, or memory timing expert , ive always had BSOD's when ive tried messing with any of that , so ive tended to throw money at the problems for an easy life. slightly embarrassing, but I want as little fannying around with the system as possible so I can actually race

Ive been testing on Detroit Belle isle circuit as it seems pretty demanding compared to some , so get it right here , should be better on less demanding tracks was my theory.

My problem is ive got so many graphs and numbers now im actually confusing myself as to what is happening. Some tools are showing my CPU bouncing off 100% , some are showing iRacing only using about 48% , all the time my GPU is sitting there twiddling its thumbs it seems.

Ive made one fairly big discovery this morning though based on things ive read on the iRacing forums.....my avg FPS on Belle isle went from 105 to 143 just by turning off HT in the BIOS...was not expecting that !


Take this grab of my Desktop as an example , whilst iRacing idling on another screen , in race on track



Its showing all the iRacing threads and total processor %'s. There appears to be 2 main threads ( cyan and yellow ) with red being total processor
The resource monitor in the background ( Green graphs ) shows all the CPU's kinda maxed
That looks pretty bad ?

However the process explorer shows iRacing only taking 48%ish of CPU ?

Looking at MSI afterburner after disabling HT I get this ( look at the timeline where the fps picks up to 140 as the game was minimised up until this point and then i run a few laps.....interestingly , even minimised on track , the CPU and GPU loads dont change...probably expected , just my lack of understanding )



Stilll the GPU seems to be only 50% utilised.

I also did a screen cap of all my meters whilst running a lap of Belle isle....have to be honest not 100% sure what these are telling me.

And thats pretty much as far as ive got....not sure what other tools or tests to run , or whether what ive done proves im CPU bottlenecked before I revisit VR on my index.




Ive been looking at these as options -
CORE I7-9700K 3.6GHZ (COFFEE LAKE) SOCKET LGA1151 PROCESSOR - 4.9GHz Single Core Max Turbo £355.99
or at a push
CORE I9-9900K 3.6GHZ (COFFEE LAKE) SOCKET LGA1151 PROCESSOR - 5.0GHz Single Core Max Turbo £479.99

OR

AM I OVERTHINKING ALL THIS

 

[Tetras]

If I'm right that this is an old not optimised engine, then those CPUs high clocks would help you, but if you had an equivalent (or near) clock speed on your current CPU, then it won't do anything at all if the engine isn't multi-threaded, because the fundamental architecture of 4th and 9th gen CPUs is near identical.

CPU bottlenecks usually result in 100% CPU load, with lower lows (like it can be single digits or sub-30 FPS) with stutters and jerky movements. At the other end of the scale, if you want to push your FPS higher (like for high-refresh gaming) then once the graphics card can handle the settings and the engine, I'd be astonished if your GPU can't, then a faster CPU will continue to push up your average FPS.

In older engines I would guess your CPU will be handicapped by your memory and the low turbo clocks, both can certainly go much higher than that. I'd consider buying some fast 16GB memory that you can keep for your upgrade if it doesn't help (your motherboard says it can handle running up to 3200) and overclocking that CPU. If you have backed up your data then you have nothing to lose by giving it a try. Your CPU is unlocked so it'll be pretty easy. I personally would hate to throw £400+ (you'd need a new motherboard) at this.

What are you actually trying to achieve, or to eliminate, by the way? I'm assuming you need higher average FPS, but what for?

 

[groove200]

Yes so although iRacing is multi-threaded , it pretty much runs on 2 main threads as far as I can understand, there are other threads for audio and such much they are much less demanding , physics and render engine seem to be the 2 big hitters ( and I see this monitoring the threads ...2 heavy ones , several smaller ones )....hence the advice ive been given to get max speeds on cores rather than more cores. Sounds right , but i dont really fully understand how time slicing works and whether more cores is better or not.

My main aim here is better VR experience , Ican hit 120fps on my index with just me on the track now ive disabled HyperThreading ( made a huge difference ) , but im seeing hitches now and then , which isnt great when barrelling into a corner
Adding other players/AI and it tanks to unplayable levels.

Ive just done some testing in VR , at 120hz, just me , and the boxed areas are the section i was driving



CPU looks maxed and im guessing holding me back when i introduce other players / AI

 

[Robert896r1]

For sims you only need a 9600k and max out the oc. Then hand tune your ram.

This is true for ac, acc, pc2, iracing, rf2, etc

 

[gavinh87]

What res are you playing at?

 

[groove200]

@gavinh87 Samsung 49" 32:9 @ 3840x1080

Good news though....with some help I entered the dark world of Overclocking for the first time....and im stunned at what ive got out of this CPU tbh.....all my problems are now resolved running at 4.8Ghz across 4 cores ( disabled HT ) and completely stable. Saved myself a whole bunch of money and learnt a lot in the process

 

[Orange Nexus]

@gavinh87 Samsung 49" 32:9 @ 3840x1080

Good news though....with some help I entered the dark world of Overclocking for the first time....and im stunned at what ive got out of this CPU tbh.....all my problems are now resolved running at 4.8Ghz across 4 cores ( disabled HT ) and completely stable. Saved myself a whole bunch of money and learnt a lot in the process

That CPUZ single bench score is pretty much what i get with my R5 3600 @ 4.2.