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My Intel (2019) MBP shows severe CPU usage when connecting to monitor(s) via a Dell D6000 Docking Station. It is OK if there are two regular monitors (1920x1200 resolution), but if I connect to a single very large resolution monitor (5120x1440), everything monitor-related lags quite a lot, and the DisplayLinkUserAgent process necessary for that specific docking station draws plenty of CPU. Even on the smaller monitors, if I just wiggle a browser window up and down quickly with the mouse, the driver takes 50% or more of CPU.

I also have a small "dongle" with a HDMI port, but unfortunately this does not work with that MBP and big monitor (there is a signal, just consisting of horizontal stripes), so I cannot really test the performance.

Is this a general issue on MacOS when transferring video signals over their USB-C ports? Or does this depend a lot on the specific dongle/docking station used? Is it worth it to shop around for a faster adapter, or can you even suggest one which has super low CPU req's?

The specs of the MBP are:

  • 13", 2019, two thunderbolt 3 ports
  • 1.7 GHz Quad-Core Intel Core i7
  • Intel Iris Plus Graphics 645 1536 MB
  • 16 GB 2133 MHz LPDDR3 RAM
  • MacOS 13.1

When I'm talking about the "dongle", I mean an Apple USB-C Digital AV Multiport Adapter. This is the one that doesn't seem to work with a 5120x1440 display (but works perfectly fine for any other monitor I have ever thrown at it) - granted, the store page says it works only for lesser resolutions, but I had it a long time before that monitor, so this is just an aside. I'm mainly concerned about the CPU usage aspect in this question, not about the limitations of this AV adapter.

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  • How about saving me some time and update your answer with more information about your MBP. Core i5, 7 or 9? Processor speed in GHz? Screen size? Does it have Touch? Apple produced 15 different MBP models in 2019. Mar 13, 2023 at 9:52
  • Easily done, @DavidAnderson, I have added the specs.
    – AnoE
    Mar 13, 2023 at 13:17
  • How do you connect two regular monitors (1920x1200 resolution) to the dock? DisplayPort or HDMI? Can I assume the very large resolution monitor (5120x1440) is connected by HDMI? Mar 13, 2023 at 13:21
  • The term “dongle” used here is a bit confusing. A dongle can be a USB video interface (USB-A/C) where it’s a whole new video adapter separate from the on board GPUs or it could be a Type-C display port to DisplayPort/HDMI cable where the native video only is transferred. Can you provide some more details on these dongles specifically?
    – Allan
    Mar 13, 2023 at 15:36
  • I've added a link to the adapter that I have, @Allan.
    – AnoE
    Mar 14, 2023 at 9:44

2 Answers 2

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Question: Do different HDMI dongles give different CPU usage on an Intel MBP?

Answer: Yes.

Question: Is this a general issue on MacOS when transferring video signals over their USB-C ports? Or does this depend a lot on the specific dongle/docking station used?

Answer: This is a issue when you install and use third party software to drive external displays. I would not recommend using third party software when an alternate configuration which relies more on the Mac's native hardware is available. In your case, you do not have to use any third party software.

Question: Is it worth it to shop around for a faster adapter, or can you even suggest one which has super low CPU req's?

Answer: You do not need a faster adaptor in order to use your existing monitors. I would recommend using a HDMI dongle or dock where there would be zero CPU usage on your Intel MBP. Currently, you are getting CPU usage because you are using DisplayLink. This is unnecessary since your Mac hardware can natively support all the configurations given in your question.

Possible solutions for configurations given in the question.

  • Two regular monitors (1920x1200 resolution)

    Connect one monitor to an USB-C port on the Mac. Here, the Mac's GPU would be either sending DisplayPort directly through the Mac's USB-C port to the monitor.

    Below is a example image of how the USB-C port would be configured inside the Mac. USB-C has 4 high speed lanes. (In the cable, each lanes exists as a pair of wires.) All four lanes are available to send DisplayPort from the Mac's GPU to the monitor. Since DisplayPort comes directly from the GPU, there is 0 usage of the CPU. Also, no data can be travel by USB.

    4-Lane DP

    Connect the other monitor to a HTML port on an USB dock, which can be connected to an USB-C port on the Mac. The dock needs to be capable of receiving DisplayPort directly the Mac's GPU through the Mac's USB-C port. Here, the dock would would be sending the received DisplayPort to a builtin HDMI adaptor before sending to the monitor.

    Below is a example image of how the USB-C port would be configured inside the Mac. Two lanes are available to send DisplayPort from the Mac's GPU to the dock. Your Mac uses DisplayPort version 1.2, so the video would be limited to 4K@30Hz. Since DisplayPort comes directly from the GPU, there is 0 usage of the CPU. The DisplayPort received by the dock would need to be converted to HDMI by an internal adaptor before sending to the monitor. Two lanes are also available for USB. This limits the USB to 10 Gb/s. USB is not used for video.

    1-Port USB + 2-Lane DP

    Since one of your regular monitors (1920x1200 resolution) has an HDMI input, then you could use your existing Dell D6000 Docking Station, provided you do not have the DisplayLink software installed on your Mac. Or, if you can prevent the installed software from being used. Note: the D6000 uses USB 3.1 Gen 1 (USB 3.0) which limits the USB to 5 Gb/s.

  • A single very large resolution monitor (5120x1440 resolution)

    You have indicted this monitor requires a HDMI connection. With this in mind, connect this monitor to an USB-C port on the Mac through a USB-C to HDMI adaptor rated for at least 5K@60Hz. The adaptor specification should explicitly state DisplayPort Alt mode will be used. As in the previous example, all 4 USB-C lanes would be used for DisplayPort.

    (Optional) Connect a USB-C dock to the other USB-C port on the Mac. Do not connect any monitors to the dock. As in the previous example, only 2 USB-C lanes would be used for USB. The remaining 2 USB-C lanes would unused.

    You could use your existing Dell D6000 Docking Station. The DisplayLink software would not need to be installed on your Mac.

Table of Additional External Display Support for 2019 MacBook Pro Models

2019 MacBook Pro DP Additional External Displays
• 13-inch
• Two Thunderbolt 3 ports
1.2 • One display with 5120-by-2880 resolution at 60Hz at over a billion colors
• Up to two displays with 4096-by-2304 resolution at 60Hz at millions of colors
• Up to two displays with 3840-by-2160 resolution at 60Hz at over a billion colors
• 13-inch
• Four Thunderbolt 3 ports
1.2 • One display with 5120-by-2880 resolution at 60Hz at over a billion colors
• Up to two displays with 4096-by-2304 resolution at 60Hz at millions of colors
• Up to two displays with 3840-by-2160 resolution at 60Hz at over a billion colors
• 15-inch
• Four Thunderbolt 3 ports
1.4 • Up to two displays with 5120-by-2880 resolution at 60Hz at over a billion colors
• Up to four displays with 4096-by-2304 resolution at 60Hz at over a billion colors
• 16-inch
• Four Thunderbolt 3 ports
1.4 • Up to two displays with 6016‑by‑3384 resolution at 60Hz at over a billion colors
• Up to four displays with 4096‑by‑2304 resolution at 60Hz at over a billion colors

† The DisplayPort (DP) version on your Mac.

References

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  • After our discussion in the comments, this sums up the situation perfectly. I have verified that with two different "cable adapters" (USB-C -> HDMI and USB-C -> DP) most combinations work exactly as you post. I do have to fiddle around with reduced resolutions for the very big monitor (maybe a different question), but the CPU usage is gone completely, and the behaviour of all my devices can be reconciled with your explanation perfectly. Awesome answer!
    – AnoE
    Mar 14, 2023 at 17:48
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Yes, this depends quite a lot on the specific dongle/docking station.

Basically there's two ways this can work:

  • Method A - Native Connection:

    The dock is connected to your MBP transferring the native display signal from the computer and onto the monitors. This is typically with a Thunderbolt dock with DisplayPort signal in the alternate mode of the USB-C connector.

    This has a relatively low impact on CPU performance.

  • Method B - DisplayLink connection:

    The dock is connected to your MBP transferring data packets coming from your MBP and translating them into a display signal on its own. This is typically with cheaper USB-C docks.

    This has a relatively high impact on CPU performance, as the computer will basically have to maintain a "virtual display" and uses the DisplayLinkUserAgent third party driver program to transfer that to the dock.

You're currently on Method B - Display Link. I would advise getting a suitable dock that offers you native connectivity instead.

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  • Cool, thank you! I had never paid attention to the fact that those ports are not pure USB-C ports, i.e. that Thunderport physically contains the connections and electrical protocols for DisplayPort on top of USB-C. There seem to be simple adapters out there which presumably are purely passive, just changing the form factor. I'll check one of those out.
    – AnoE
    Mar 13, 2023 at 13:31
  • jksoegard: I believe with Thunderbolt 3, the DisplayPort data is included in the Thunderbolt data. DisplayPort alt mode is not employed. With USB, using alt mode is optional. If you read the manual for the D6000, you will discover the dock can use both DisplayLink and alt mode simultaneously. If you do not install the DisplayLink software, then only alt mode is available. Mar 13, 2023 at 15:39
  • Not quite.. with Thunderbolt 3 the maker of the dock basically has two options, they can use DisplayPort Alt Mode (similar to USB-C DisplayPort alt. mode) or they can use Thunderbolt Alt. Mode. The MBP supports both alternatives. Most monitors only support DisplayPort Alt. Mode, while some Thunderbolt-branded monitors support Thunderbolt Alt. Mode. Note that in neither case is "the displayport data included in the Thunderbolt data" - the intuition that the displayport signal is somehow converted to data packets that are "mixed together" with Thunderbolt data is incorrect.
    – jksoegaard
    Mar 13, 2023 at 20:06
  • And yes, the D6000 dock supports running both as a DisplayLink dock and driver-less with just USB-C Displayport Alternate Mode. However, it lists that last alternative as only working with the HDMI output (not the DisplayPort outputs), and only at 4k 30 Hz. I.e. it won't work with the 5120x1440 display resolution in the question here.
    – jksoegaard
    Mar 13, 2023 at 20:07

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