DisplayLink Impact on CPU and GPU

[mgrayeb]

Hello,
I have an HP Omen 15 laptop with two secondary 14" monitors. One of those displays is powered by USB, and the other is powered by Thunderbolt (USB-C).

When I plug both of those monitors into the laptop, my understanding is that the laptop is using DisplayLink technology to display whatever content is shown on the monitors; is that correct?

If yes, can you please give me a sense of what kind of impact that has on the GPU and/or CPU of the laptop?

The reason I ask is because I'm doing live streaming with the laptop using a software product called vMix, streaming to both Facebook and YouTube, and sometimes bringing in remote guests using WebRTC video calls inside of vMix, and also sometimes simultaneously bringing in an additional guest and screen sharing via the Zoom meeting platform.

I am not using the laptop for gaming, but rather for video panel discussions with multiple guests as outlined above, along with graphic frames containing the guests for the live streaming show. I hope that is clear.

My understanding from vMix support is that using USB and USB-C powered displays might slow down vMix so it is not recommended.

Thank you.

[AlbanRampon]

Hello,

Would you have some precisions on the setup you have, or think about?
Resolutions for for both displays you connect on the Thunderbolt and what is on USB (if you have already a USB device, you can give me the name/ref).

What you describe is a similar use case to what millions are using their docking station for: video conferencing.
I looked at the software online. For the DisplayLink workload, I think it will look like playing a video with VLC. Depending on the DisplayLink hardware you are using, and your machine, we will leverage CPU or GPU. Our algorithm is adaptative, so we use what's there to achieve the framerate and latency we wish. If the machine is busy, we relieve pressure.

Does the machine has an Intel integrated GPU or just the big nVidia RTX 2070?
With more displays, your Windows desktop will be bigger, so Windows will give more work to your GPU (in all screens, the GPU still composes the desktop). That's why I am asking about the resolutions involved.
If you give me the reference of the machine, I can have a look at the memory as well. For high resolution, dual-channel RAM is recommended: a lot of data to shuffle quickly!

I see your machine should be able to drive 3 displays (embedded + HDMI + miniDP) out of the box.
That's a very nice machine!

Kind regards,
Alban

[mgrayeb]

Hello,
Thank you for your reply.

Below are the specs on my Omen 15T laptop, HP product # 4FB29AV. My understanding is there are no integrated graphics (Optimus); only the GTX 1060 graphics card.

In terms of the USB-powered 14" display, and the Thunderbolt-powered USB display, both have 1920 x 1080 resolution and here are the links to those, respectively:
USB 14" HP display: https://store.hp.com/us/en/pdp/hp-v1...rtable-monitor
Thunderbolt 14" HP display: https://store.hp.com/us/en/pdp/hp-el...rtable-display


Omen 15T Laptop Specs:
•Windows 10 Home 64
•Intel® Core™ i7-8750H (2.2 GHz, up to 4.1 GHz, 9 MB cache, 6 cores) NVIDIA® GeForce® GTX 1060 (6 GB GDDR5 dedicated)
•16 GB DDR4-2666 SDRAM (1x16GB)
•15.6" diagonal FHD 144 Hz IPS anti-glare micro-edge WLED-backlit (1920 x 1080)
•1 TB 7200 rpm SATA; 256 GB PCIe® NVMe™ M.2 SSD
•No Optane
•Office Software Trial
•Security Software Trial
•4-cell, 70 Wh Li-ion polymer
•No DVD or CD Drive
•Full-size backlit keyboard with numeric keypad and N-Key Rollover (White Legend)
•HP Wide Vision HD Camera with Dual digital microphone
•Intel® 802.11b/g/n/ac (2x2) Gigabit Wi-Fi® and Bluetooth® 5 Combo(MU-MIMO supported)

In my vMix Live Streaming Software, I would probably offload the encoding for the streaming and the recording to the nvenc hardware encoder on the graphics card but I could have one or both of those handled by the cpu; depending on whether DisplayLink is more likely to draw from CPU or GPU and whether it is likely to have a significant impact on either, if that makes sense. My understanding from vMix technical support is that the camera inputs, video files, titles, and images in my live stream show are generally handled by the GPU, whereas the WebRTC video calls (of which I would likely have 4 simultaneously), NDI input of animated titles from a program called Titler Live, and Desktop Capture (audio and video screen capture) of Zoom meeting would be handled more by the CPU.

From vMix Support:
"Both the 1060 and 2060 are very similar. The 2060 is a bit better being a more recent release. But when it comes to vMix and your particular show setup, there isn't much difference. Especially as you don't have many inputs using the graphics. The CPU is a little bit more important in your setup due to using vMix Call and NDI.

Re: i7-9750 vs. i7-8750 - again both very similar. With the i7-9750 being a bit better and a more recent model. What you want to look for is the Ghz value of the CPU. I'd recommend 3.6GHz plus.

The RAM in the system isn't important when it comes to vMix.

What I do want to ask about is the use of a USB and thunderbolt monitor. Is this because you are wanting to use a laptop and need more than 2 displays? If any of these displays use the CPU instead of the Graphics, this actually slows things down alot for vMix. So isn't recommended."


By the way, I have recently ordered a second HP Omen 15 laptop to be used either to offload some of the tasks above and/or to be used to handle all tasks instead of the above-referenced laptop. I'm not sure if the specs on the forthcoming unit impact your response as I suspect they are very similar, but just in case, here they are:

Product number: 7LG50AV
•No DVD or CD Drive
•1 TB 7200 rpm SATA; 512 GB PCIe® NVMe™ M.2 SSD
•Full-size island-style white legend 4-zone lighting RGB backlit keyboard with numeric keypad and 26-Key Rollover
•Security Software Trial
•32 GB DDR4-2666 SDRAM (2x16GB)
•Intel® Wi-Fi 6 AX 200 (2x2) and Bluetooth® 5 Combo (Gigabit file transfer speeds)
•Office Software Trial
•Windows 10 Home 64 ADV
•HP Wide Vision HD Camera with integrated dual array digital microphone
•15.6" diagonal FHD 60 Hz IPS anti-glare micro-edge WLED-backlit (1920 x 1080)
•6-cell, 69 Wh Li-ion polymer
•Intel® Core™ i7 9750H (2.6 GHz, up to 4.5 GHz, 12 MB cache, 6 cores)+NVIDIA® GeForce® RTX 2060 (6 GB GDDR5 dedicated)
I'm not sure whether or not the forthcoming laptop will have integrated graphics or if it will strictly have the RTX 2060 dedicated card, but I suspect the latter.

Please let me know if you need any additional information from me. Thank you very much.

Kind regards,


Mike

[AlbanRampon]

Hello Mike,

Thanks for the details. Very helpful.
I don't believe the USB-C display is Thunderbolt. I believe it is using DisplayPort Alternate-Mode (DisplayPort signals over USB-C plug). Using TB for 1080p would be an expensive overkill, limiting compatibility of the display.
The device with DisplayLink technology is also Full HD, which is easy to handle on any machine nowadays.
Our chip in this device would run with the CPU, but, as it's only HD, I don't expect your machine to sweat at all: we've been showing 4x4K and 8x4K desktops for productivity on a single USB 3.0 port.

Your CPU has an H which is supposed to mean High end UHD 630 graphics, but HP might have not enabled it. If it does have an Intel GPU (see in Device Manager under Graphics Adapters), I recommend you move all your applications to the nVidia GPU (in Settings > Display > Graphics settings). 3 full HD displays will make your Nvidia GPU laugh.

I'd say RAM does matter when you are running multiple software you wish to run fast, and 16GB is good for that. The new one is better, not only because you have more RAM (which may not be used), but because it will be dual-channel (it's not explicitly said, but I expect it to be). Dual-channel means more bandwidth, which is significant when you have a lot of data to shuffle. Personally, I would only buy dual channel machines now.

I'm surprised the refresh rate was decreased on the new machine.
Have you seen much impact of the 144Hz on the current one? I'm curious as I don't play games, where I believe it is supposed to have most visible benefit.
I am interested in your feedback, as this can help us steer developments.

Kind regards,
Alban

[mgrayeb]

Hello Alban,
Thank you again for your reply.
When I shared your previous reply with the developer at vMix, here was his reply:

"Hi Mike,

The "a lot of data to shuffle quickly!" is the key point to the performance issues with USB displays.
They need to first render on the GPU, then copy that data back to the CPU, then encode it over USB.
This process of downloading from a GPU is quite slow compared to upload and hard to get right, and we have spent years trying to optimise for it.
If another application tries to do the same thing while vMix is running it throws all our optimisations out the window and leads to random and unpredictable high render times, especially on laptops.

It is for this reason we do not support or recommend USB connected displays.

Kind Regards,

Martin
vMix"

Alban, any thoughts on Martin's concerns? My guess is it's going to come down to real-world testing on my part. I've been overtasking the laptop while running vMix (running Titler Live, Zoom meeting, and multiple vMix Call sessions simultaneously while streaming to two destinations) and periodically I've noticed CPU and/or GPU overload warnings in vMix but I think that may in part have been caused by overheating of the laptop, which, from what I've gathered from user reviews and my own experiences, seems common in the HP Omen 15 series. Now that I have a cooling pad I'm hoping some of that might be mitigated but I may need to offload some tasks to a second computer, e.g. the forthcoming laptop.

Re Your question on my experience with the refresh rate: I don't do any gaming at all, and I think I purchased the 144 Hz refresh rate display option more out of ignorance on my part than anything else. I was thinking I might need to do some screen capturing of my display to bring into my live stream so I wanted to ensure I would'nt have any tearing or other issues but I'm guessing for my needs and since I don't game that it was an overkill choice. That's why I only selected the 60 Hz refresh rate display option on the laptop I recently ordered.

Separately, it appears from your most recent reply to me that the HP Elite 14" display that is powered by USB-C does not use DisplayLink technology, and I don't see that model as listed on the DisplayLink website. I guess I was mentioning Thunderbolt-powered because a consumer or two had posted reviews on HP's website for that unit complaining that the unit requires Thunderbolt but maybe they were misinformed.

Also, I checked the Display Adapter in the Device Manager and the Intel Integrated Graphics is not listed; only the nVidia graphics card. I also checked the display settings and there was no option there to disable integrated graphics or direct everything to the nVidia card so my sense is I'm all set there.

I'm hoping you're correct about the dual channel RAM and that it will be helpful to me in my use case.

Thank you again for your helpful reply.

Kind regards,


Mike

[AlbanRampon]

Hello Mike,

HD is not what I would call a lot of data, even at 60 fps.
You were mentioning the machine can struggle already, but you could also look at the memory usage when you have your stress situation and who is consuming that memory via Task Manager.
From what I can see, the Opal and Ruby reference systems advised by the software vendor for HD both are dual-channel, because it makes sense.

But I can confirm that no pixel comes free of computation.

The USB-C DisplayPort Alternate-Mode (Alt-Mode) "USB" display is directly driven by the GPU. There's no encoding over USB or things like that (because they are not really USB) and this is the reason why, for instance, they cannot be connected through USB hubs. It still consumes GPU though.
I think there is a confusion about technologies and protocol. The USB-C plug itself does not mean the transport is USB traffic. I could simplify what "Alt-Mode" means by "Not USB traffic over the USB-C plug". It requires specific hardware on the platform, on top of USB.

We've been fitting HD on USB 2.0 with 10y old machines.

Kind regards,
Alban

[mgrayeb]

Thank you Alban for your detailed explanation. I do see, upon checking the specs for the HP Elite 14" display, that in the footnotes it mentions a requirement for either Thunderbolt or DisplayPort Alt Mode.

I am plugging the USB-C Cable from that display into the Thunderbolt port on my laptop, but perhaps that port also has DisplayPort Alt capabilities built-in that are not called out in the laptop's specs and perhaps the display is using that technology in this case instead of defaulting to Thunderbolt, even though it's plugged into a Thunderbolt port?

If yes, then based on your comments, my understanding is that it would only be using the Graphics Card's resources, and not the CPU's resources. If that's correct, then my sense is that it would not be simultaneously (alongside vMix) downloading data from the GPU to the CPU during my live stream and thus I wouldn't be at risk of throwing off the vMix opitimization of that process and the resulting high render times during my live streams.

I guess the way to confirm whether the display is only using GPU resources would be to monitor both CPU and GPU usage in the task manager when connecting the display.

And then, similarly, monitoring impact on CPU and GPU with the other 14" display that I have (the USB-powered one that employs DisplayLink technology) and whether that might be simultaneously trying to download data from the GPU to the CPU while vMix is doing the same -- although I appreciate your point about the minimal amount of data involved in the case of an HD (1920 x 1080) display.

I hope I've understood your comments correctly and again thank you for your help.

Best regards,


Mike

[AlbanRampon]

Yes, you have.

Thunderbolt 3 ports feature DisplayPort alt-mode, but DisplayPort alt-mode ports don't necessarily have Thunderbolt 3 capability.
In all cases, the USB-C plug MUST at least have USB.

I found slide 21 on this article showing the data path.

Kind regards,
Alban