CPU bound vs. GPU bound

[scommander2]

Hi,

I would like to understand more about CPU bound vs. GPU bound, and what are pros and cons?

In order to gain or get a stable FPS, should DCS use CPU bound more than GPU bound or vice versa? Or, how to balance them? Or, it has to depend on the physical hardware?

Thanks.

 

 

[Hiob]

There is no "better". Unless you artificially cap the fps at a fixed refresh rate you will always be limited by one or the other.

The question about what the limiting factor in any given situation (scene) is, is only relevant, if you want to decide on an upgrade.

E.g. it doesn't makes sense to upgrade you GPU, if you are severly bottlenecked by your CPU most of the time.

Be carful though. Some telemetry reporting "CPU limited" can also mean, that there is for example an FPS cap enforced. Which would be governed by the CPU and therefore reported as CPU limited. Be sure to open the gates before reading any telemetry with this in mind.

[Hiob]

On second reading of your Question:

You can, to an extend, influence the load on CPU or GPU. In a nutshell, "eye candy" like shadows, draw distance, lighting, textures etc. are straining the GPU, texture resolution (and therefore size) affects the VRAM need.

CPU is strained by lots of scripting or a ton of AI units. Also secondary tasks, like putting out telemetry (minor load), running other stuff in the background and so on.

[scommander2]

Hi @Hiob, thanks for the comments and replies and I need time to re-think about the suggestions.

[diego999]

10 hours ago, Hiob said:

There is no "better". Unless you artificially cap the fps at a fixed refresh rate you will always be limited by one or the other.

The question about what the limiting factor in any given situation (scene) is, is only relevant, if you want to decide on an upgrade.

E.g. it doesn't makes sense to upgrade you GPU, if you are severly bottlenecked by your CPU most of the time.

Be carful though. Some telemetry reporting "CPU limited" can also mean, that there is for example an FPS cap enforced. Which would be governed by the CPU and therefore reported as CPU limited. Be sure to open the gates before reading any telemetry with this in mind.

This is good advice.

 

In general you want to be GPU limited, as there is a lot of eye candy you can chop down in order to get more frames.

In a CPU limited scenario there is not a lot you can do to gain performance.

[The_Nephilim]

Well and my question is how do you tell you are GPU Limited, I always here many answers to this question and never really found what is true about it..

[Hiob]

8 hours ago, The_Nephilim said:

Well and my question is how do you tell you are GPU Limited, I always here many answers to this question and never really found what is true about it..

Well that is actually pretty easy. Given you use the right tools.
First that comes to mind is the integrated telemetry of DCS. Ctrl+Pause gives you the FPS and when you expand, it actually shows you what the limiting factor is (make sure you are not limited by a fps-limit).
Another way is to use the Afterburner/Riva Overlay and see if the GPU is fully utilized (97-100%). If limited by CPU, the GPU may only be used by 50-70% or so......

Without an kind of utility or telemetry analysis, it is indeed impossible to tell whether you are limited by CPU or GPU....

[Hiob]

Actually the ingame FPS counter explicitly tells you how you are bound and by what. Just checked

[Hiob]

For me (potent GPU but slightly outdated CPU) it fluctuates wildly between GPU and CPU bound. 

Edited Friday at 09:53 AM by Hiob

[draconus]

You need to understand that the CPU and GPU frame times depend highly on the scene, the mission and settings (both in DCS and external software/drivers). Be sure to test different maps, missions and settings as these can create totally different results.

If the GPU ends its frame creation it still has to wait for the CPU to display it and vice-versa. Thus best case is when the two match more or less. But it's not possible for all cases. If you see "CPU bound" most of the time it means you can use higher graphic settings without affecting the fps.

[Moxica]

9 minutes ago, draconus said:

If you see "CPU bound" most of the time it means you can use higher graphic settings without affecting the fps.

That is what I (think) I've experienced. -Was CPU bound. Pushed eycandy up.. Also running Pimax @120Hz.
Visible range to extreme. Got better graphics AND a fluid flight experience.

[Raven (Elysian Angel)]

3 hours ago, Hiob said:

For me (potent GPU but slightly outdated CPU) it fluctuates wildly between GPU and CPU bound. 

In VR or 2D?

Personally I am “CPU bound” 100% of the time in VR, even in a free flight mission on an empty map. This was the case with my old 5900X and still is with my current 9800X3D. GPU usage is 93-94%, and I can indeed push visibility range without affecting framerate.
When I test a mission in 2D, I’m “GPU bound” 100% of the time.

[draconus]

2 hours ago, Raven (Elysian Angel) said:

Personally I am “CPU bound” 100% of the time in VR

It's all fine until you get below target fps Does that happen?

[Raven (Elysian Angel)]

Just now, draconus said:

It's all fine until you get below target fps Does that happen?

I’m not claiming it’s a problem. I just find it curious to be “cpu bound” even with a 9800X3D. That tells me there’s something else going on, irrespective of users’ hardware.

My frame time graphs are basically flat lines so I’m not complaining

[draconus]

2 minutes ago, Raven (Elysian Angel) said:

I just find it curious to be “cpu bound” even with a 9800X3D.

That depends on settings and if you have fps cap set it will say CPU bound too.

[Hiob]

3 hours ago, Raven (Elysian Angel) said:

In VR or 2D?

Personally I am “CPU bound” 100% of the time in VR, even in a free flight mission on an empty map. This was the case with my old 5900X and still is with my current 9800X3D. GPU usage is 93-94%, and I can indeed push visibility range without affecting framerate.
When I test a mission in 2D, I’m “GPU bound” 100% of the time.

2D. I fly VR very seldom.
But of course VR has different needs than 2D.

Generally speaking. ED improved the CPU utilization a lot lately. I used to be GPU limited, even on a 4090 for the longest time. Now I often find myself CPU limited. I don't have a "gaming" CPU though. "Just" a 5900X.
  

[scommander2]

a dumb question:

All (or most) DCS computing tasks are done at CPU not GPU (not CNN, or DLSS stuff)? Right?

[The_Nephilim]

17 hours ago, Hiob said:

Well that is actually pretty easy. Given you use the right tools.
First that comes to mind is the integrated telemetry of DCS. Ctrl+Pause gives you the FPS and when you expand, it actually shows you what the limiting factor is (make sure you are not limited by a fps-limit).
Another way is to use the Afterburner/Riva Overlay and see if the GPU is fully utilized (97-100%). If limited by CPU, the GPU may only be used by 50-70% or so......

Without an kind of utility or telemetry analysis, it is indeed impossible to tell whether you are limited by CPU or GPU....

well I had seen the expanded DCS tool many times but not sure where you say it shows you the limiting factor, where does it say that in the DCS Tool? I will check the GPU Usage but curious about the DCS tool?

 

I also use VR so I guess in a way I am FPS Limited but I am not sure if I am or not.. the FPS seemed locked at 60fps. IF that is the case not sure what more horesepower would do for me?

[Bounti30]

Hello everyone. Since version 2.9.15, I've been limited by my graphics card. I'm using Quest 2 with Link, and all my drivers are working fine.
My system is an i9 9900k, an RTX 3090, 64GB of RAM, and a 1TB NVMe SSD. My operating system is Windows 11.
My settings in DCS aren't optimal. I'm using OTT with supersampling at 1.3 and openXR toolkit turbo mod.
Why is this high GPU usage ?

My flight, only me with a P51 on Marianas WWII Map

My CPU usage is correct

 

My log

dcs.log

Thank you

[Hiob]

12 hours ago, The_Nephilim said:

well I had seen the expanded DCS tool many times but not sure where you say it shows you the limiting factor, where does it say that in the DCS Tool? I will check the GPU Usage but curious about the DCS tool?

 

I also use VR so I guess in a way I am FPS Limited but I am not sure if I am or not.. the FPS seemed locked at 60fps. IF that is the case not sure what more horesepower would do for me?

I’m not quite sure if I get the issue here. When you open the fps counter in DCS and press the little arrow to expand it, you get a graphic representation of your frametimes and above that it says in clear text what is currently holding you back (and even why and what your theoretical fps would be without the bottleneck).

Sure in VR you are locked to a fixed frame rate (intentionally), and if you never drop under your desired target fps you certainly don’t need an upgrade, however, most people will experience occasional drops below the desired threshold when facing demanding circumstances.

 

2 hours ago, Bounti30 said:

Hello everyone. Since version 2.9.15, I've been limited by my graphics card. I'm using Quest 2 with Link, and all my drivers are working fine.
My system is an i9 9900k, an RTX 3090, 64GB of RAM, and a 1TB NVMe SSD. My operating system is Windows 11.
My settings in DCS aren't optimal. I'm using OTT with supersampling at 1.3 and openXR toolkit turbo mod.
Why is this high GPU usage ?

My flight, only me with a P51 on Marianas WWII Map

My CPU usage is correct

 

My log

dcs.log 120.34 kB · 1 download

Thank you

DCS utilizes the CPU much better since the introduction of MT. And they continue to improve it since then. And if you are bottlenecked by your GPU, where is the problem? Also I don’t see a single core maxed out…..

[Bounti30]

18 hours ago, Hiob said:

DCS utilizes the CPU much better since the introduction of MT. And they continue to improve it since then. And if you are bottlenecked by your GPU, where is the problem? Also I don’t see a single core maxed out…..

I'm bottlenecked by my  GPU since 2.9.15

Before this update, there were no problems.
Identical settings in DCS, no additional mods, up-to-date Nvidia and Quest drivers, etc.
What happened?

[Hiob]

Well, remote diagnosis is always difficult matter

First of all, being bottlenecked isn’t inherently a problem. It is inevitable.

If you’re fps haven’t got worse, I would just assume that DCS is better utilising you CPU now. Otherwise, …. I don’t know. There could be a ton of reasons….

[Raven (Elysian Angel)]

9 minutes ago, Hiob said:

First of all, being bottlenecked isn’t inherently a problem. It is inevitable.

That’s what many people don’t seem to get: you’re always bottlenecked by something, or you’d have infinite fps

[Hiob]

26 minutes ago, Raven (Elysian Angel) said:

That’s what many people don’t seem to get: you’re always bottlenecked by something, or you’d have infinite fps

…and what you are bottlenecked by can virtually change by the direction you‘re looking at…..

[AndyJWest]

9 minutes ago, Hiob said:

…and what you are bottlenecked by can virtually change by the direction you‘re looking at…..

Yup, and that is how a balanced system is likely to behave. Looking at blue sky and ocean unloads the GPU, so the CPU is the limiting factor. Down low over complex ground details, the GPU may hit its limits first. Maybe once in a while you'd hit near max load on both CPU and GPU, but it is likely to be transient.