Experiencing performance problems with Dell XPS 15 and USB C Dock (UD-CA1)


#1

Whenever I attempt to listen to streamed audio when connected to the dock I experience major performance issues. Typically this involves the CPU percentage for “Interrupts” rising to > 10% and overall CPU usage rising to 100%.

I do not see the same issues when disconnected from the dock (with all other factors remaining the same). Is this just a reality of this technology? The only other device attached to the dock is my monitor which is running at 2650x1440. I’m using the most recent DisplayLink driver from Pluggable.

Overall, even without the obvious issue when streaming audio the machine seems noticeably slower when attached to the dock (I’m running CPU heavy workloads and they consistently take longer to complete when attached to the dock), but that is mostly anecdotal at this point since it is hard to precisely quantify.


#2

Hello Sean,

Sorry to hear about this issue. I’d be happy to help.

First, let’s uninstall the DisplayLink driver because the UD-CA1 does not use DisplayLink technology.

Secondly, what program are you using to stream audio when the dock is connected? And are you connected to the Internet via WiFi or using the Ethernet connection on the dock.

Lastly, when you see the CPU workload go up, what process is taking up more CPU?

Thanks,
Josh


#3

Josh, hi.

I’m working at home today so I don’t have the dock, but I’ll try things tomorrow with the DisplayLink driver uninstalled.

As for the other details, I’ve experienced issues using both Pandora and Stitcher. I’m connected via WiFi.

When I get the lockup, 100% CPU issue it is marked by a rise in the percentage of time taken by “Interrupts”. When I’ve observed the general slow down I can’t really pin it on anything (which is why I consider that to be anecdotal at this point, since I can’t pinpoint the cause). I’ll try to see if I can pin that down a bit tomorrow as well.

Thanks,
Sean


#4

Josh, hi.

Quick update – the first issue (locking up when streaming audio) appears to be fixed now that I’ve removed the DisplayLink driver. However, the second issue (an overall performance penalty on my primary workload) is still there. I still don’t see an obvious culprit for this one, though I have a couple of theories I’m going to try out later today.

FWIW, the workload I’m using to measure this is a compilation and running of tests for our code base. Normally this takes about 10-12 minutes to run, but when I’m connected to the dock it takes 14-16 minutes. So far this result has been consistent (if a bit mysterious).

I’m assuming that this isn’t something you’ve seen before. Thanks for the help.

Sean


#5

Josh, hi.

I believe I have pinned the performance issue down. It appears to be related to the amount of power provided by the dock. When I run connected to my adapter I get better build times than when I’m powered through the dock (even when the dock is doing nothing else). This despite the fact that it appears to recognize that it is connected to a power supply and I’ve switched the power profile to use 100% of the CPU – still seems to lag.

One of the reasons for buying the version with power delivery was so I could avoid having to hassle with a second adapter (not to mention the added cost). However, it appears this is only supplying 60W to the laptop and as a result it isn’t able to run at full performance. This appears to be a somewhat known thing as I happened to reboot when powered by the dock and Dell’s BIOS popped up a warning about the reduced power supply.

Is the 60W output a limit of the USB PD spec, this particular dock, or Dell’s PD implementation?

Thanks,
Sean


#6

OK, so I poked around a bit more and it seems the PD spec allows up to 100W, but the web description of the dock clearly states that it provides 60W. I knew this might impact charge rate, but didn’t realize it would impact performance. Unless I’m missing something I think it is running the best it can at this point. Unfortunately since this impacts something I do several times per day I’m going to have to look for a different solution.

Thanks,
Sean


#7

Hello Sean,

Sorry for my delayed reply. Glad to hear that removing the DisplayLink drivers helped with the audio.

60W is the current limit for USB-C Power Delivery. No 100W devices are available yet. The best solution to prevent the CPU from throttling back to reduce power consumption to fit within a 60W profile will probably be you needing to use the stock charger for your system while the dock is attached (the system will default to charging from that, not the dock).

Thanks,
Josh


#8