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When run Time Spy the laptop display, even if 2 external 4k monitors are enabled (with nothing happening on them) I still get a 3D Mark score of around 9500.

If I disable the internal monitor and other external monitors and just run TimeSpy on 1 4K display I get around 8000.

I've run this multiple times and it's always the same, no major other processes are running.

Any idea why this might be? According to this link this should not happen: https://support.benchmarks.ul.com/support/solutions/articles/44001789016-does-my-desktop-resolution-affect-my-3dmark-score-#:~:text=The%20rendered%20frames%20are%20then,the%20desktop%20resolution%20you%20use.

Thanks

niico
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1 Answers1

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Your laptop has video outputs wired to a different GPU than the one you're running 3DMark on. The internal display, on the other hand, is wired to that GPU. The usual setup on laptops with higher-end graphics would be internal screen wired to the integrated GPU and video outputs to the dedicated GPU.

In this configuration if 3DMark is running on a display that the screen is wired to, then entire PCI-e bandwidth is available for 3DMark. However if the display is connected to a different GPU, then rendered frames have to be sent from the rendering GPU to the displaying GPU. That consumes part of the PCI-e bandwidth. Ironically the more frames you get, the more bandwidth (and thus frames) you lose - it's a negative feedback loop.

15% performance loss is roughly what you should expect based on the results of eGPU folks.

gronostaj
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  • Interesting thanks, so generally on a laptop you'll get this? How come this doesn't happen on desktops? I have a desktop and get max performance on any of my monitors... – niico Sep 14 '22 at 20:56
  • @niico On a desktop you usually have all your displays physically connected to a single GPU, so there's no "penalty" for transferring frames to a different GPU. But as I said it's a thing with eGPUs: you have to connect a display directly to them to get full performance. Also low-end graphics cards aren't affected because they aren't fast enough to saturate PCI-e. That's why laptops with low-end GPUs usually have all their outputs connected to the integrated GPU. It makes things a bit easier on the driver/power saving side. – gronostaj Sep 15 '22 at 05:24
  • Thanks. Sorry I'm not using an eGPU, the RTX 3080 GPU is inside my laptop, it's the mobile version. Or are you also referring to that as an eGPU? (I thought eGPUs were desktop GPUs housed in a casing attached to a laptop through thunderbolt)? – niico Sep 15 '22 at 13:10
  • Is this what a MUX switch helps with? – niico Sep 15 '22 at 13:12
  • Yes, we have the same definition of eGPU and I know that you're not using one. But it's an analogous situation: two GPUs (iGPU + dGPU/eGPU), each with its own video outputs and the display is connected to a different one than the one doing rendering. It doesn't matter if they are integrated, dedicated, external etc. Say that the display is connected to GPU1 and rendering is done on GPU2. The rendered frame must somehow get from GPU2 which created it to GPU1 which will be displaying it and the only way to do that is by sending it over PCI-e. Yes, a mux switch could help. – gronostaj Sep 15 '22 at 13:31
  • I've solved it, should have mentioned this but didn't think about it. The lower perf external display was going from USB C (high quality thunderbolt 3 cable) into a dock. The dock was then using DP into the monitor. I just tried this on displays directly connected to HDMI and DP on the laptop instead of going via the dock. Now the perf is just as good on those external monitors. So I guess the dock was the issue somehow. – niico Sep 15 '22 at 13:54
  • My thoughts are why aren't external monitors just treated like the internal display and given signal in the same way that is? Just like it would be on a desktop?! The internal display is just a display right?! If there's no mux switch and there's a perf hit, the internal display would get the hit too no? If not how does it avoid that but external displays don't?! – niico Sep 15 '22 at 13:56
  • Sounds like my guess was incorrect in this case, then. Why not just like on a desktop? Because on a desktop you have one GPU and this whole problem is nonexistent. In a laptop it's a completely different situation: you need an iGPU for power saving and a dGPU for performance. Each display output can be wired to one and only one of them. Internal display must go to the iGPU. Otherwise the dGPU would have to be active all the time to drive the display, and that would be a waste of power. […] – gronostaj Sep 15 '22 at 14:22
  • For external display outputs as a laptop designer you have to choose between (a) wiring them to dGPU: better performance on external displays, worse performance on internal display, higher power usage when a display is connected; or (b) wiring them to iGPU: better performance on internal display, worse performance on external displays, same power usage when a display is connected. The former makes more sense for a couple of reasons: […] – gronostaj Sep 15 '22 at 14:27
  • (1) you may need more performance for high-resolution high-framerate external displays, (2) you'd rather have full performance on a large screen than a small screen, (3) if you're using an external display you probably have a power adapter around and power consumption isn't that big of a deal, (4) when you're playing on the go the laptop won't run at full tilt anyway because the battery can't provide that much power so you're getting less FPS, so the shared bandwidth issue gets less severe – gronostaj Sep 15 '22 at 14:31
  • Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/139226/discussion-between-gronostaj-and-niico). – gronostaj Sep 15 '22 at 14:41
  • I do have a desktop though I travel about 6 months a year so have to use the laptop then and managing and syncing 2 devices that I use for development and video rendering too as well as gaming (in addition to paying to upgrade them) is quite time consuming and expensive. I'm amazed how powerful and portable the Razer Blade 14 is, so for me I can now have everything in 1 machine. I don't need the absolute best performance but 9500 3d mark is pretty decent, even for VR (which is what I mostly use it for). Indeed my laptop is very close in perf to my desktop (3900X with 2070 Super). – niico Sep 15 '22 at 14:46
  • Interesting points though. I never game on battery, though I do work on battery and need to move around a lot so a sleek laptop like this makes sense in my situation. Also owning fewer large things in life is nice IMHO. – niico Sep 15 '22 at 14:47