How does CPU influence VR when high resolution gaming is GPU bound?

wunkley · 16 Apr 2021 at 18:33

As title.
Can anyone provide personal experience with data to back it up or provide me with good links please?

I'm genuinely confused regarding VR performance with regards to the CPU. As I understood it, and as any benchmark review has shown for years, once you get to 4k 60Hz gaming the GPU is always the 'bottleneck' and there is minimal difference in FPS and performance between an old but decent overclocked 6 core 12 thread CPU (like my 5930k) and a modern 6 core 12 thread CPU.

The reverb G2 is essentially almost x2 4k resolution, so how can a CPU upgrade have any meaningful impact on performance when a game must be GPU bound at such high resolution? People seem to say that VR is different and a CPU upgrade would help. How when ultra high res gaming is entirely GPU bound?

I'm currently on a 5 year old intel i7 5930k overclocked to a v decent 4.6Ghz, with a 3090FE. VR performance on the G2 in Flight Sim 2020 has given me the upgrade itch.

And specifically, For VR in Flight Sim 2020, would there be any point upgrading from my current CPU to an intel 11400 for example? All the CPU benchmark comparisons I see are only ever at 1080p or 1440p max. This tells me nothing for gaming at 4k or VR higher res....

stephenb · 16 Apr 2021 at 18:57

Because you are rendering the scene from two different view ports. That means the work done by the CPU (often bound to a single thread for rendering) is up to double as it has to handle twice the amount of draw calls, culling etc, and in preparing the command lists before dispatching everything off to the GPU for rendering to the displays in your headset. There are vendor specific features, such as single pass stereo from Nvidia, which seek to reduce the work required by the CPU in drawing the scene twice but as you can imagine implementation is not universal and it requires specific models of GPU.

wunkley · 16 Apr 2021 at 19:22

stephenb said:
Because you are rendering the scene from two different view ports. That means the work done by the CPU (often bound to a single thread for rendering) is up to double as it has to handle twice the amount of draw calls, culling etc, and in preparing the command lists before dispatching everything off to the GPU for rendering to the displays in your headset. There are vendor specific features, such as single pass stereo from Nvidia, which seek to reduce the work required by the CPU in drawing the scene twice but as you can imagine implementation is not universal and it requires specific models of GPU.

Thanks! Just the kind of answer I was looking for.

For VR specifically then, would you know or be able to reason out how my current oldish 6c/12thr 5930k at 4.6Ghz might compare to a 6c/12thr intel 11400 (seems an amazing budget option) or perhaps an 8c/16thr 10700k in Flight Sim 2020 in VR specifically? Would either help to bolster up the minimum FPS? If so by what amount? I'm looking for significant gains to consider the expense and hassle of a motherboard and cpu upgrade....

DD_Crash · 16 Apr 2021 at 19:56

I would ask this on a MSFS2020 forum, they should be able to give you the info

stephenb · 16 Apr 2021 at 21:14

wunkley said:
Thanks! Just the kind of answer I was looking for.

For VR specifically then, would you know or be able to reason out how my current oldish 6c/12thr 5930k at 4.6Ghz might compare to a 6c/12thr intel 11400 (seems an amazing budget option) or perhaps an 8c/16thr 10700k in Flight Sim 2020 in VR specifically? Would either help to bolster up the minimum FPS? If so by what amount? I'm looking for significant gains to consider the expense and hassle of a motherboard and cpu upgrade....

Can't answer for MSFS specifically, racing sims are my speciality, but my last upgrade was from a 4930k to 3900x and I did see moderate gains in CPU bound scenarios. I have a Rift CV1. Currently on the look out for a 5950x, but only buying at RRP.

newuser · 16 Apr 2021 at 22:03

Also can't answer for MSFS but I believe it's still constrained by single core thread performance. There haven't been massive IPC gains for Intel in a long while. I'd be tempted to wait for them to sort their software out before going to the effort of upgrading. Do a session with HWinfo running and see where your bottlenecks are.

Anecdotally, I had a 4790k, 2400mhz ram and a 1080 which was struggling in VR despite being a well balanced setup. I went 10700k, 3200 ram but kept the 1080 while waiting the new 30 series cards. The difference was marginal. The 1080 was allready maxed out. Snagged a 2080ti when people were selling them off. A bit meh to be honest. The 3090 was a decent improvement when I got one and the system seems well balanced again. Like I said, find your bottleneck and consider the effort required.

Andy D · 17 Apr 2021 at 08:52

4K gaming isn’t usually considered as high framerate gaming. In VR it is

muzzler · 17 Apr 2021 at 10:16

There's a good Facebook group for msfs2020 VR that would be worth joining. Theyre a helpful bunch.
I run msfs on an i7 9700F with a 3090 and it can struggle with fps in some areas. (limited by main thread error pops up a lot then)
The thing with that sim is, that there is no guarantee that anything will run smoothly! lol. The general opinion is that it's a sim that demands a lot and can be temperamental..a bit like the missus!