Possible influencing factor for stuttering / spiking frame times on new GPU generation (nVidia RTX, AMD RX)

[Rifter]

I have been testing a 3090 and a 6900xt in the last weeks on my rig - was running a water cooled 1080ti before (the system itself is an Asus Z390 Maximus Gene with an overclocked 9900K and 32GB kit of DDR4-3600 with very tight timings).

 

I tested both a Rift S and a Reverb G2.

 

During my testing I made the following observation:
Either letting the GPUs doing their job in the out-of-the-box configuration or alternatively overclocking the GPU manually created in both cases a tendency towards stuttering and very pronounced frame time spiking for both vendors though the green team doing significantly better here.

This was very surprising for me since I used the identical graphics settings I had for my 1080ti which didn’t show any stuttering. I expected those settings to be a piece of cake for the flag ships cards of team green and red.

 

So I started to play around.

 

Fixing the clock rate by a defined voltage (aka undervolting) on the 3090 eliminated all frame time spiking and stutters.
On the 6900xt it helped a lot to prevent the GPU from using the out-of-the-box efficiency behaviour (which is very aggressive on RDNA 2) by forcing it to stay within a defined clock rate speed (when the CPU struggles with filling the draw call pipeline Big Navy seems to drop into a short power saving sleep).

 

The difference to the out-of-the-box behaviour is basically one thing: The GPU doesn’t boost anymore. And the boosting process itself seems to be counterproductive in DCS VR.

 

Looking back to my old GPU this somehow confirms my observation: My 1080ti had several manually optimised voltage curves which I made for specific applications and saved as profiles in afterburner. One curve was exclusively for DCS and it definitely never let the GPU go into boost.

 

Since I don’t want to generalise my experience I would like to hear some more voices here.

 

Anybody here with a similar experience?

Since heavily overclocked and maxed out GPUs are not uncommon for VR users - anybody with stutters in VR (and an overclocked GPU) willing to try an undervolting approach and report his results?

 

Edited July 16, 2021 by Rifter
typo

[PicklePicklePickle]

Wow, I haven't done this but I'm definitely going to try it now. Can you elaborate on exactly what you changed on the 3090 and what tools you used? I have experience overclocking CPUs in the BIOS but I have never messed with GPU overclocking/undervolting.

 

I will give it a try and let you know.

[Rifter]

The community member speed-of-heat as a neatly worked out guide for VR users.

https://forums.eagle.ru/topic/257819-my-3090-settings-for-my-g2-271/

Coincidentally he has the same GPU model as I (EVGA 3090 XC3). He uses an overclocking curve to keep his card over 2 GHz @ 993mV when I interpret his curve correctly. Being around 1V is definitely not the sweet spot for any 3090 out there - that is actually pushing the pedal to the metal. I his case it seems to work so nothing wrong with it.

 

However when I overclock my card to 2 MHz my system sporadically creates frame rate spikes due to small variances in GPU clock speed which again seems to influence the VR frame rate.

 

What I did instead: I keep my GPU around the sweet spot (in my case 837 mV @ 1830 MHz). As a result I lose around 200 MHz of possible clock speed but also gain absolutely constant frame times. No more erratic stutters in VR. I could not find any disadvantages because of not having the max clock speed possible on my GPU. As a side note: The graphics engine of DCS does not create a huge wattage draw in VR - it’s only around 220W in my case.

 

Now for your question:
I use MSI Afterburner as undervolting tool. It can be used with any GPU brand. You can easily choose a specific voltage point in the curve editor and fix your clock rate to that voltage. As a conservative starting point for a 3090 you can use 875 mV @ 1845 MHz. Lots of guides out there for the usage of afterburner. The curve editor of Afterburner is not very intuitive because of it’s poor UI but it only takes a couple of seconds to set up a specific curve. When you are familiar with CPU overclocking in the BIOS then that will be a piece of cake for you - much more easier than CPU overclocking.

 

The final result depends on the specific binning of your GPU aka silicon lottery. Mine is only mediocre so YMMV.

 

It seems that a lot of people are overestimating the benefit of maxing out FPS on their cards. Especially in the case of the top tier nVidia Ampere cards.
And for VR it is not primarily about FPS - it’s more about frame times as well as frame time variance. Hunting for FPS is only a thing when you don’t have any overhead for your required minimum frame rate. But then it’s probably better to reduce settings before you max out the GPU.

Edited July 24, 2021 by Rifter

[darkman222]

That sounds very interesting but logical on the other hand too. I have a lot of CPU frame time issues. Most of them seem to come from multiplayer CPU load. I almost gave up and my weapon of choice became 60 Hz mode for the Pimax. I never really thought about overclocking the GPU because I know the CPU is bottlenecking my system.

But going the other way underclocking sounds interesting.

I might want to give it a try when I have time for that. Thanks for the detailed post so far.

[javelina1]

On 7/24/2021 at 10:25 AM, Rifter said:

The community member speed-of-heat as a neatly worked out guide for VR users.

https://forums.eagle.ru/topic/257819-my-3090-settings-for-my-g2-271/

Coincidentally he has the same GPU model as I (EVGA 3090 XC3). He uses an overclocking curve to keep his card over 2 GHz @ 993mV when I interpret his curve correctly. Being around 1V is definitely not the sweet spot for any 3090 out there - that is actually pushing the pedal to the metal. I his case it seems to work so nothing wrong with it.

 

However when I overclock my card to 2 MHz my system sporadically creates frame rate spikes due to small variances in GPU clock speed which again seems to influence the VR frame rate.

 

What I did instead: I keep my GPU around the sweet spot (in my case 837 mV @ 1830 MHz). As a result I lose around 200 MHz of possible clock speed but also gain absolutely constant frame times. No more erratic stutters in VR. I could not find any disadvantages because of not having the max clock speed possible on my GPU. As a side note: The graphics engine of DCS does not create a huge wattage draw in VR - it’s only around 220W in my case.

 

Now for your question:
I use MSI Afterburner as undervolting tool. It can be used with any GPU brand. You can easily choose a specific voltage point in the curve editor and fix your clock rate to that voltage. As a conservative starting point for a 3090 you can use 875 mV @ 1845 MHz. Lots of guides out there for the usage of afterburner. The curve editor of Afterburner is not very intuitive because of it’s poor UI but it only takes a couple of seconds to set up a specific curve. When you are familiar with CPU overclocking in the BIOS then that will be a piece of cake for you - much more easier than CPU overclocking.

 

The final result depends on the specific binning of your GPU aka silicon lottery. Mine is only mediocre so YMMV.

 

It seems that a lot of people are overestimating the benefit of maxing out FPS on their cards. Especially in the case of the top tier nVidia Ampere cards.
And for VR it is not primarily about FPS - it’s more about frame times as well as frame time variance. Hunting for FPS is only a thing when you don’t have any overhead for your required minimum frame rate. But then it’s probably better to reduce settings before you max out the GPU.

 

I have a 3090FE, and have an MSI profile for DCS, (and the other sim), set at 825mV & 1815 MHz.  My G2 fly's along just fine, locked at 45fps.   Plus, by GPU temps when in DCS are around 48-51C, and the memory is around 82-84C.  I really do like the benefits of undervolting, indeed...   As you noted, I do NOT see any sort of erratic stutters in VR.  I know I could probably push and squeeze my undervolting further, but it's been solid, and that's what counts.

 

for grins, I also have a profile for what I call just desktop mode.  where the mV & MHZ are dialed down further.  my GPU temps are around 37-38C & memory is roughly 62-64C.

[darkman222]

I gave it a super quick try right now. I was undervolting as much as MSI afterburner allows. If undervolting would make an impact I on my rig I should have experienced it in tonights DCS session. But unfortunately there was no relief for the CPU. FPS VR just showed the same patterns of the CPU bottlenecking in multiplayer.

[javelina1]

14 hours ago, darkman222 said:

I gave it a super quick try right now. I was undervolting as much as MSI afterburner allows. If undervolting would make an impact I on my rig I should have experienced it in tonights DCS session. But unfortunately there was no relief for the CPU. FPS VR just showed the same patterns of the CPU bottlenecking in multiplayer.

hi darkman, what are your rig specs?  in particular, your CPU?

[darkman222]

Ryzen 9 5900x not overclocked. And an RTX 3090. 32GB of RAM. Using FPSVR i can see most of the time the CPU being the bottleneck. Until we got the new clouds it always was the CPU being the issue.

[Rifter]

On 7/27/2021 at 2:26 AM, darkman222 said:

I gave it a super quick try right now. I was undervolting as much as MSI afterburner allows. If undervolting would make an impact I on my rig I should have experienced it in tonights DCS session. But unfortunately there was no relief for the CPU. FPS VR just showed the same patterns of the CPU bottlenecking in multiplayer.

Yes - no undervolting or overclocking can solve that typical DCS problem.
What I had in mind were those strange VR performance issues which are not explainable from being CPU bound or having too ambitious graphics settings.

Should have been more precisely here.

 

Thanks a lot for your contribution anyway!

[DucS2r]

I have a relatively new rig with a 3090 FE as well and after spending a few weeks tuning everything for my Reverb G2 was happy with the performance, solid 45 FPS with mainly high settings. I just undervolted my GPU as noted, and ended up at 800mv at 1815mhz. There were other settings that were similar, but I like that one. No loss of performance and much greater stability. It isn’t hard to do and everything is reversible. 

[javelina1]

48 minutes ago, DucS2r said:

I have a relatively new rig with a 3090 FE as well and after spending a few weeks tuning everything for my Reverb G2 was happy with the performance, solid 45 FPS with mainly high settings. I just undervolted my GPU as noted, and ended up at 800mv at 1815mhz. There were other settings that were similar, but I like that one. No loss of performance and much greater stability. It isn’t hard to do and everything is reversible. 

Very nice!

[Harlikwin]

Very interesting. 

[darkman222]

I must confess this is pretty stupid, but some of my stutters came from thermical issues that were caused by upgrading from a 2080 to a 3090.

I noticed that the airflow that was good with the 2080 got as bad as with the 3090 that the PC stopping to work suddenly due to CPU self protection. I am pretty sure the CPU was throtteling down a lot before it shut itself off.

So guys, be smarter than me and check if you airflow and CPU temperature is still good.