GPU and CPU utilisation in VR

[sam75]

I was surprised to see that my Titan X P sits at average around 42% usage when using the Oculus Rift CV1.

Just done a basic test sitting in front of a station in space, GPU usage is only 43%, yet the Oculus Dev tool performance monitor shows a performance headroom of between -5 and 15% with the odd few dropped frames.

Surely the GPU should be working harder if that is the case?

My CPU is running at around 70 to 80% utilisation during this. RAM 4.6gb of 16gb used.

I would be interested to see what others are getting? Is this a case of poor optimisation of the game, or some kind of CPU bottleneck?

My specs:

GPU - Nvidia Titan X P running latest 727.70 driver
CPU - Intell I5 6600k @ 4.6 ghz
RAM - 16gb DDR4 2133 mhz
OS - Windows 10

In Game settings

GFX - Ultra (default settings but Blur disabled, SMAA, SS at 1.0)

cheers [up]

 

[Darkmark07]

Are you looking at CPU utilisation per core or overall?

Dunno if ED is multi-threaded so you might find that it's fully utilising 1 CPU core and therefore bottle-necking there.

Just a thought.

Could also be Oculus runtime consuming CPU cycles - again not sure if it's multi-threaded or not...

What about PhysX? Is that assigned to the GPU or CPU in nVidia CP?

 

[Soopyyy]

Yeah, even without running VR, ED uses a LOT of CPU.

 

[[HJ]-RedRaven]

I was surprised to see that my Titan X P sits at average around 42% usage when using the Oculus Rift CV1.

Just done a basic test sitting in front of a station in space, GPU usage is only 43%, yet the Oculus Dev tool performance monitor shows a performance headroom of between -5 and 15% with the odd few dropped frames.

Surely the GPU should be working harder if that is the case?

My CPU is running at around 70 to 80% utilisation during this. RAM 4.6gb of 16gb used.

I would be interested to see what others are getting? Is this a case of poor optimisation of the game, or some kind of CPU bottleneck?

My specs:

GPU - Nvidia Titan X P running latest 727.70 driver
CPU - Intell I5 660k @ 4.6 ghz
RAM - 16gb DDR$ 2133 mhz
OS - Windows 10

In Game settings

GFX - Ultra (default settings but Blur disabled, SMAA, SS at 1.0)

cheers [up]

Youll need to post some screenshots of the Debug Tool HUDs to try to work out where the bottle neck is... although its most likely the CPU.

VR is a whole new ball game compared to the normal throw frames at the monitor to max out at 60fps (or more on some monitors).

There are timer deadlines to consider other than the simple 'have a frame ready before the next monitor refresh' in 2D.
If your cpu isn't handling the geometry load, it will miss some of the 180 frame deadlines per second (90 per eye, so 180 different geometry setups per second)... in ED at High/Ultra detail levels, that's a LOT of work.

Missing a deadline for geometry means you'll fail back to ATW-supplied warped frame... and as that only takes 5ms or so, your video card will sit idle for a while until the next geometry frame is ready. That's 'probably' why its sitting at 43% usage.

VR is hard on CPU cache too - sequential 2D frames following each other are more similar and suffer fewer cache 'misses' than stereo frames with two different viewpoints (we think of them as similar but it may as well be two completely different camera angles because each eye's geometry calcs don't know about each other at all). Stereo is harder because cache misses are higher = even more work for the cpu as its thread prediction success is lower.

Lower the geometry detail and you might see the video card work go up.

 

[Seneleron]

I have no idea what the GPU utilization is on my 1080, but I CAN tell you that my 6700k @ 4.7 hovers around 23-24% +/- a few%

As for Graphics settings, there is a VR specific setting in the options. Ultra seems to be for standard 2d monitors, and DID cause some performance hiccups for me early on when I tried it.

Also, if you're not yet aware, watch out for the Oculus/elite dangerous memory leak.

 

[sam75]

Thanks for the responses, some really interesting info there. I will have a play around again later with different settings.

I did run VR High before, but tried Ultra and found it looked so much better, with little or no perceptible performance hit, it is only when using the debug tool that you really see the difference in FPS and performance headroom.

 

[dape]

any news on this?

I turned ASW on and within a station I get 45 FPS most of the time. CPU load about 50% and GPU 90 to 100% with temps around 68C (GTX 980 OCd).
But sometimes the framerate drops to 22 and it stutters badly. GPU load drops to about 50%. Dunno why it is doing that, as I don't see any limits beeing reached. Sometimes I just have to wait a bit and FPS go back to 45.

i5 6600k @4.2GHz
980 OCd
16G Ram

 

[[HJ]-RedRaven]

dape -

With ASW enabled, even a 1080GTX will see 45fps in stations except at very low detail. I think the ASW cut-in threshold is set a little low and it drops to 45fps too early - I get better framerate just leaving it on Ctrl-Numpad 1 mode (just ATW). ASW also mashes the menus up when you navigate around.

Otherwise the pauses usually mean ED is just loading something, or waiting on network/server traffic. In Open play, other players can enter and leave your instance, and approaching planets etc, entering stations can all cause hiccups. NPC's are created (and deleted) too. If any of these interrupt the VR rendering

Obviously, other programs you're running or utilities in the background like virus scanners, firewalls and ad-blockers etc can also impact performance.

The gpu under-utilisation happens because of the way VR imposes timers on when the gpu starts rendering a frame. Using the App Render HUD in the debug tool will show you what time its taking for your cpu and gpu to render a frame.

There's less of the smooth continuum of frame rates you see in 2D when you change settings. In VR the 90fps fixed clock and queue-ahead timers mean there's suddenly a big jump down to 45fps, and changes in detail settings can mean no performance impact at all, unless you're close to the timer limits and a settings change suddenly causes a lot of dropped frames (then ASW kicks in).

 

[dape]

Thanks for the explanation. I just got my Rift a week ago and have not much knowledge about the technical datails. Was just curious, why it suddenly at unregular time intervals stutters just sitting in the station.