CPU v GPU bound

[DavidE]

My current system is a 3080ti / 9900K / G2 / triple 32 1440, I find it reasonably balanced in terms of being GPU v CPU limited, depending on the situation. For triple use, not a huge need to upgrade but would like to play more VR which is not ideal at present. Would like an AMD gen 5 + 4090 but at present can afford only one of these. I am trying to understand the interrelationship between being CPU and GPU bound.

situation 1 - game is GPU bound

If I upgrade the CPU will I get any benefit if the GPU is the limiting factor or will the CPU take off some of the load from the GPU leading to better FPS

situation 2 - game is CPU bound 

If I upgrade the GPU, presume I will gain little in terms of  FPS but would I be able to up the resolution of the G2 while keeping similar FPS.

Not sure how CPU and GPU limits interact, can anyone help with practical experience?

I play mainly the 3 main flight sims plus racing sims such as ACC, the latter works well with the triples. Also some games such as COH3 when it comes out.

Third option is a newer headset but think the market needs to progress a year or two and will still have marginal performance.

Thanks

Edited February 16, 2023 by DavidE

[edmuss]

The definition of CPU bound can be interpreted a number of ways in DCS VR, my take on it (from a VR performance perspective) is if the CPU is taking longer to composite the render than it is the GPU.  This will manifest in the CPU frametime being higher then the GPU and the resultant fps being below the indicated GPU frametime.  This is of course not taking into account additional CPU load such as AI, mission scripts and simply the current single threaded nature of DCS.

I upgraded from a 3600@4.3ghz / 3070 to my current rig of 5800x3D / 3080ti in two stages, first the CPU then the GPU.

My experience was that simply changing the CPU resulted in 25% performance across the board, this was from a GPU that was running at 95% load beforehand and in free flight missions.  I had never been CPU bound (by my definition above) in a free flight mission, yet the upgrade made a massive difference; this was very suprising as I was only expecting a few % at best.

Upgrading the GPU was from a desire to be able to run higher settings with better framerates (and the lad desperately needed a GPU upgrade for his birthday so he got the 3070 and I was wife sanctioned to buy myself a new GPU ).

I believe that you will see a significant increase by going to a newer CPU, even if it's a 5800x3D and stick with the 3080ti.  With tweaking and setup I can get 8-15ms GPU frametimes on Syria with generally high settings, MSAAx2 and shadows on high/flat.  With the release of the DLSS I believe that this performance will improve as it should give a better image then the current NIS upscaling that I'm utilising.  Go for the CPU, if you can push budget for ryzen 7xxx and DDR5 then that will future proof you but I suspect (and hope) that the 5800x3D/3080ti combo has some legs left for DCS yet

[Supmua]

2 hours ago, DavidE said:

My current system is a 3080ti / 9900K / G2 / triple 32 1440, I find it reasonably balanced in terms of being GPU v CPU limited, depending on the situation. For triple use, not a huge need to upgrade but would like to play more VR which is not ideal at present. Would like an AMD gen 5 + 4090 but at present can afford only one of these. I am trying to understand the interrelationship between being CPU and GPU bound.

situation 1 - game is GPU bound

If I upgrade the CPU will I get any benefit if the GPU is the limiting factor or will the CPU take off some of the load from the GPU leading to better FPS

situation 2 - game is CPU bound 

If I upgrade the GPU, presume I will gain little in terms of  FPS but would I be able to up the resolution of the G2 while keeping similar FPS.

Not sure how CPU and GPU limits interact, can anyone help with practical experience?

I play mainly the 3 main flight sims plus racing sims such as ACC, the latter works well with the triples. Also some games such as COH3 when it comes out.

Third option is a newer headset but think the market needs to progress a year or two and will still have marginal performance.

Thanks

 

Trying to simplify this.

CPU: handles logic, AI, object rendering, movement, collision, assigns graphic processing tasks to GPU and has to wait until that task is done (e.g. rendering one frame) before it can move on.

GPU: handles graphic processing, shaders, textures, lightings, reports back to CPU.  Typically has tons of cores (16,384 in RTX 4090 vs a dozen or so in a typical CPU).

In general, the limiting factor is whichever has the highest frametime as the next rendered frame cannot happen until the whole process is completed.  So if your CPU frametime is 7 ms and GPU frametime is 14 ms, the final frametime will be 14 ms for that frame and the repeated processes determine the overall fps—and in this case, GPU limited which is a typical scenario for most games out there.

Personal experiences.  Going from 9900K/3090 to 9900K/4090 gives me instant 90 fps in Caucasus free flights as CPU isn’t taxed much in these type of missions.  Note that I would never hit 90 fps with any CPU in combination with 3090 because the GPU itself isn’t strong enough to produce low enough frametime (below 11.1 ms) with my current settings (3Kx3K pixels).  The fps gain is reduced in complex maps such as Marianas or crowded MP mission because CPU frametime takes more hits in those scenarios, and this is alleviated after I upgraded my 9900K CPU to 5800X3D.  With this my min fps improves a lot while max fps stays the same (hence avg fps goes up), on average scenarios.  
 

But it gets more complex in VR because of the headset’s fixed frequency and motion smoothing.  If you use motion smoothing, unless you hit 90 fps (or whatever your headset’s frequency is), the fps will drop to the nearest multiplication factor such as 45.  Say, you currently get perfect constant 45 fps and upgrade to a system that cannot consistently hit 90 fps you will not see much benefit.  On the other hand if you’re currently below the 45 threshold and upgrading CPU and/or GPU will get you way above then smooth 45 fps gameplay will happen.

Edited February 17, 2023 by Supmua

[Willie Nelson]

@Supmua that was very well explained. Thanks. 

[edmuss]

Yeah, much better than my attempt

[DavidE]

Thanks for the comprehensive replies, looks like both options will have benefits even if bound by the other component. Tending to think I will go for the CPU first with a 7800X3D (subject to reviews).  Part of thinking is that the 7800X3D may be the only CPU I will ever need (said that before with 9900K!), this could be especially true if multi core is enabled. In a years time the GPU market may have moved forward with a 4090Ti or something and perhaps slightly lower prices for the 4080. The 5080 may also be on the horizon by that time.

If the 3080Ti works OK, it also opens up getting a Pimax Crystal or similar although same argument could be said for getting the 4090 first and DCS becoming kinder to the 9900K. Probably change my view again in a few days!

[Mars Exulte]

With that system I would stop worrying about it altogether. DCS' issue is not hardware related, it's software. It's not going to get better, and doesn't matter how much raw power you throw at it, until they update the engine (hopefully coming soon).

[slaxor]

Hey guys. I was very puzzled with this situation too but in relation to IL-2. It appears that DCS and IL-2 have the same issue because they are single-threaded. CPU bound scenario occurs at 50-60% CPU load (per core) which sucks. So there is no way to identif/see it because windows will roll thread across all core without any gains though. Actually, the only way to see it is CPU-frametime, for example in fpsVR. Before fpsVR I could not see any reason why I'm not getting 90 fps.

Take a look at this IL-2 forum with very good explanation: https://forum.il2sturmovik.com/topic/82991-is-it-worth-upgrading-my-cpu-and-ram/?do=findComment&comment=1256972 It also has a sheet with CPU bound performance (See 1080 test).

Basically, CPU performance of both games can be predicted on "Single Core Performance" of a CPU. Dev do have to fix it. It is definitely software problem and it is getting ridiculously critical in achieving 90fps in VR.

BTW do we have similar sheet for DCS. I'd anticipate that DCS will be less performant.

[Mr_sukebe]

I'll say it again.  It's possible to offload "some" of the load on the CPU for single player persons who run their own missions, by hosting a standalone server on the same PC (or nearby one if you have a spare), and then logging into it as you would any online server.

The implications being that the dedicated server conducts the calculations for AI pathfinding and logic, leaving your CPU core to for your own side of things.  It won't provide significant benefit on simple missions, but can allow the running of significantly more complex ones.

[Willie Nelson]

On 2/27/2023 at 8:52 PM, Mr_sukebe said:

I'll say it again.  It's possible to offload "some" of the load on the CPU for single player persons who run their own missions, by hosting a standalone server on the same PC (or nearby one if you have a spare), and then logging into it as you would any online server.

The implications being that the dedicated server conducts the calculations for AI pathfinding and logic, leaving your CPU core to for your own side of things.  It won't provide significant benefit on simple missions, but can allow the running of significantly more complex ones.

That's a pretty expensive way of uping performance. I take your point though. 

[Mr_sukebe]

22 hours ago, Willie Nelson said:

That's a pretty expensive way of uping performance. I take your point though. 

If you have a PC with 64GB of ram, you can run it on the same PC that you run the client on.  

[slaxor]

On 2/27/2023 at 8:52 PM, Mr_sukebe said:

I'll say it again.  It's possible to offload "some" of the load on the CPU for single player persons who run their own missions, by hosting a standalone server on the same PC (or nearby one if you have a spare), and then logging into it as you would any online server.

The implications being that the dedicated server conducts the calculations for AI pathfinding and logic, leaving your CPU core to for your own side of things.  It won't provide significant benefit on simple missions, but can allow the running of significantly more complex ones.

It sounds actually a bit controversial. The worst performance drop in FPS AFAIK we get when playing online missions, e.g. servers like Enigma. My understanding if above was the case then Online servers would be faster than single missions which is not the case. Am I missing something?

[Dragon1-1]

Yes, actual multiplayer has, well, multiple players. This adds further load, not to mention large MP servers typically have a lot of AI ground units and the like. SP missions are more restrained, if you can shove AI to its own core, you can squeeze out some performance.

[crispy12]

Go 4090 if you want to play VR and enjoy the full experience. Even a 3090ti will struggle (a little bit), a 3080ti will only be playable at settings most people coming from monitor can't accept. 

A CPU helps of course, but the difference a GPU makes for VR is massive. CPU will smooth out the stutters and also ease the load on multiplayer maps with a lot of assets. If anything, the future multithreading patch may make this a non-issue.

[jnr4817]

I just upgraded to a 4090 from 1070ti. Specs are 8600k at 5g, 64g ram 3200, m.2 drives, and rift s.

I was getting 27fps with ASW and low settings on the 1070ti. 
 

With the 4090 I’ve maxed all settings and turned off ASW and am getting 80fps consistently without any dips.

Its truly a new experience. No stutters, smooth, clear, totally amazed. 
 

The 4090 is worth it if your budget allows. Waiting to see how this 7800x3d thing shakes out compared to 13th gen intel. Will probably upgrade cpu next year.