60 FPS Gaming - CPU Pairing with GPUs

[tential]

We all know that you generally need a good CPU to drive high frame rates. But if we set 60 FPS as our target frame rate, when does a CPU bottleneck us from reaching this target?

Are these ST or MT cases?

Really, how much CPU power do we actually need for driving a GPU before it bottlenecks us from hitting a measily 60 FPS?

 

[ZGR]

Depends on the game I guess. My favorite RTS game of all time only needs a mid range GPU from 2013 or new iGPU for 4k max settings, but it will need a CPU 4x faster than a 5.2 GHz i7 8700k for 60fps as it loads all the AI on 1 core.

Even newer games like GTA V with 10x Traffic + Pedestrians I am CPU bottlenecked at 4k ultra as my CPU is bottlenecked because it only has 4 cores. This results in 40 fps at times.

Same is said for Fallout 4 and many other games allowing mods. Even Elite Dangerous has an awful ST bottleneck on planet surfaces even at 4k Ultra.

My favorite game for high framerates is Rainbow 6 Siege, which I game on my 180hz display. I am always CPU bottlenecked at around 200 fps, and streaming further reduces performance.

Destiny 2 is another title that cannot sustain 144hz in Coop scenarios due to CPU MT bottleneck.
Even ARMA 3 cannot maintain 60 fps with half as many AI as ARMA 2 due to more complex AI. It makes it feel like we will never have the CPU performance needed for 1:1 realistically scaled battles with individual AI units.

CPU performance is far more important in these games. It is never enough in my opinion. If I replaced my current CPU with an overclocked 6 core or 8 core, I'd increase the level of AI even further with performance staying the same. There is no CPU fast enough. They are all slow imo.

This is also why I hate canned benchmarks. Gaming at 4k with max settings will always hide the evil CPU bottleneck lurking just behind the scenes.

 

[tential]

I'm thinking more just general normal cases.

Yes, I agree completely, I always will get the fastest CPU I can. But for this build, I'm just trying to understand what the limit is. Like I wouldn't be playing GTA 5 modded on this, I would play that on my main rig. I'd play GTA 5 at normal settings.

Ya, I am worried about just looking at benchmarks, that's why I want to get some discussion on it. Like where are the 3770k/4770k unable to sustain 60 fps due to being slow CPUs and not due to the GPU?

High frame rates are out of the discussion for this as that's just a whole other build/discussion.

 

[Carfax83]

The most important factor in determining the ease at which a game hits 60 FPS, is definitely the engine. You can have the fastest CPU out there, but if the engine is crap, then getting to a steady 60 FPS will be damn near impossible. Then I think the API is secondary, and hardware comes last.

Some engines are just amazing in how well optimized they are for hardware. The latest and greatest example of this is Id Tech 6.5, which uses Vulkan exclusively. That engine is flat out incredible in how efficiently it utilizes the hardware, and how well it scales on multithreaded CPUs. With my 6900K, it's very rare that I drop below 100 FPS in the game never mind 60 FPS, even with tons of stuff happening.

And the amount of sophisticated graphical effects and the frequency at which they are used is also very impressive. For an example, the game's volumetric smoke and fog effects universally accept light and shadow from the environment. Usually this kind of effect is used very sparingly in games, because it is computationally expensive. Doom used it in fact, but not gameplay scenarios. Wolfenstein 2 on the other hand uses it very often, both in the environment and in gameplay scenarios such as the one below, which I took from the Digital Foundry video.

As you can see, the smoke from the explosion is being affected by the fire and the particles which are lit.

 

[Carfax83]

I'm thinking more just general normal cases.

Yes, I agree completely, I always will get the fastest CPU I can. But for this build, I'm just trying to understand what the limit is. Like I wouldn't be playing GTA 5 modded on this, I would play that on my main rig. I'd play GTA 5 at normal settings.

Ya, I am worried about just looking at benchmarks, that's why I want to get some discussion on it. Like where are the 3770k/4770k unable to sustain 60 fps due to being slow CPUs and not due to the GPU?

High frame rates are out of the discussion for this as that's just a whole other build/discussion.

Like ZGR said, it really depends on the game (which then depends on the engine). We are slowly transitioning from high level APIs to low level APIs, at least for the big AAA engines. Older games like GTA V are going to rely on IPC and clock speed more so than newer games like Wolfenstein 2 or AC Origins, which tend to have a much greater affinity for parallelism.

 

[PrincessFrosty]

Entirely depends on the game, each game has a different number of CPU cycles it needs to complete the next engine tick. Some are insanely heavy like for example RTS games with massive numbers of units, e.g Total Annihilation and all the spin offs over the years. Anything with lots of AI and/or real time physics. Some games use almost no CPU at all, like a 2d puzzle adventure or something like that.

I stopped thinking about CPU in terms of what's the minimum you really need and started thinking about future proofing my builds. You see with a video card newer more demanding games can simply have the video settings lowered to keep them playable. But with CPUs there's often not many game settings that can lower demand on the CPU.

So I think of it in terms of, if I buy a good CPU/RAM now it'll last me say a good 6 years before it'll be borderline needing upgrading, and then you can swap out GPUs maybe every 2 years independently. My 2600k build, that's 2nd gen i7, is what I've just replaced and ideally this rig will again last about another 6 years with 2-3 GPU swaps in that time.

GPUs are easy to upgrade but CPUs tend to cascade into needing a new socket type and chipset, then new RAM and new motherboard and then maybe new cooling and all that, so good to build it to last. If you build with a mentality of only just good enough for current demands then you'll run into bottlenecks in the near future and be stuck facing that cascade of upgrades to your system.

 

[dogen1]

I stopped thinking about CPU in terms of what's the minimum you really need and started thinking about future proofing my builds. You see with a video card newer more demanding games can simply have the video settings lowered to keep them playable. But with CPUs there's often not many game settings that can lower demand on the CPU.

2 options that stand out in terms of reducing CPU load are shadow distance/quality and view distance in general. Those shadow draw calls can add up surprisingly fast.

 

[PrincessFrosty]

2 options that stand out in terms of reducing CPU load are shadow distance/quality and view distance in general. Those shadow draw calls can add up surprisingly fast.

There are some settings in games that do load on the CPU. Typically the graphics settings do not significantly, draw calls have to be managed by the CPU but with DX12 that's a lot more efficient, and even <DX12 they don't typically take up a big percentage over the overall demand on say a mid range CPU like an i5.

I'd probably give an example of traffic density and pedestrian density in a game like GTA V, where you're increasing the amount of active AI on the screen at any one time. AI has a nasty little problem of the demand needing to increase exponentially as you add more actors as every actor has to consider every other actor. Kind of like number of players in an online MP game and their impact on the network stack.

The other really big hitters are physics, sometime PhysX can be done on the CPU and turning off pseudo liquid and pseudo cloth can help although typically that's being shifted to the GPU these days anyway.

Once you get CPU limited in most modern games you're kinda screwed, your best options are overclocking or upgrading.

 

[dogen1]

Yeah settings like car and pedestrian density in gta would help too.

 

[richaron]

My Ryzen 1700 @ stock struggles to get 20fps in Civ6 on Linux. It's a pretty good example of how a modern but (arguably) poorly optimised game on an (arguably) poorly optimised API can fail badly. Rest of the system is Vega 64, 64GB 2800 ECC RAM, 100Hz 3440x1440.

Accepted Ryzen 1700 is probably the worst case scenario for this game, but even double the horsepower will struggle to get 40fps on dem 2 threads:

As opposed to CS:GO on an old but wonderful engine (still OpenGL), which has moved the bottleneck from the CPU to the GPU: