Windows (7) Interrupts at 20%+ CPU and display tearing


#1

USB-C Plugable dock with Dell laptop, two external displays (one HDMI one DVI), Ethernet, mouse, keyboard, USB drive, USB printer attached. Mostly this works but occasionally the display and responsiveness on mouse/keyboard becomes sluggish. At this point Windows Interrupts start occupying usually about 20% CPU (four core i7), and the external displays start to exhibit a lot of tearing and refresh problems.

Unplug the USB-C, let the laptop retake control, and the CPU usage disappears. Plug the USB-C back in and it’s all OK for a while.

I’m on the M3 DisplayLink Manager, latest Windows updates and latest drivers for my laptop, including the graphics driver (or so the Dell update tells me). Also, I have resolved other issues about the Windows tearing effect with non-Aero themes so normally this really does work very well.

I haven’t quite nailed down what causes this new problem with the high CPU on Interrupts but it has come up a couple of times now - whether it is just work for a period of time or if it happens after something specific. Wondered if anyone had seen this as well?

Tx. Rob.


#2

A little more information - the 20% CPU on Interrupts seems to kick in pretty reliably on resume from suspend. The image shows two cycles of the following actions:

  1. Start with USB-C connected and all peripherals active. Interrupts=~1%
  2. Suspend Windows then Resume. Interrupts=~20%
  3. With Windows running, unplug USB-C and wait for full disconnect. Interrupts=~1%
  4. With Windows running, plug in USB-C and wait for full reconnect. Interrupts=~1%

If I suspend Windows without the dock connected, then there is also no problem.

!](https://d2r1vs3d9006ap.cloudfront.net/s3_images/1653844/plugableInterruptsCPU_inline.jpg?1506247025)](https://d2r1vs3d9006ap.cloudfront.net/s3_images/1653844/plugableInterruptsCPU.jpg?1506247025)


#3

It also appears as if sometimes unplugging the USB-C cable isn’t sufficient and the laptop has to be suspended and then resumed with the cable disconnected.


#4

Hello Rob,

Thank you for contacting Plugable support! Sorry to hear about this issue. I’d be more than happy to assist you.

We have a troubleshooting tool that helps us find out what is going on in situations like this. Please plug the dock into your computer, then go to this page and follow the instructions there:

http://plugable.com/support/plugdebug

If possible it would be great to run the diagnostics during or after one of these high CPU usage events occurring.

Also, does this happen completely randomly? Or does it seem to happen when perhaps an application is open that requires more graphics processing? (HD video playback, photo or video editing, etc) Or does this only happen if putting the system to sleep and then resuming?

Please don’t hesitate to let us know of other questions.

Thanks again for contacting Plugable support and best wishes!

Joshua Henry
Plugable Technologies


#5

Hi Josh, (Same Rob Dean but forums seemed to lose my user - couldn’t reset so have re-registered)

Thanks - I’ve run the diagnostic and emailed the zip to support@plugable.com (MCRDEAN*.zip).

The problem may occur at other times, but it will reliably occur with the sequence of plug in the USB-C dock, suspend, resume. It does not occur with the sequence of plug in the USB-C dock, suspend, unplug USB-C, resume, plug in USB-C. If high CPU is present, it will stay indefinitely but will disappear with the sequence of suspend, unplug, resume, wait a minute or two for Windows to get happy, then plug in.

I experimented with attached components but this problem will reappear with all of the components unplugged from the USB dock (initially left the Ethernet connected but disconnected both monitors, mouse, keyboard, printer, audio and a USB drive). However, when I have just Ethernet plugged in for example, after anything from about 20 seconds to several minutes, the CPU will drop back to normal. If I connect everything except the two monitors back, the same happens - may take a few minutes but CPU eventually drops back to normal.

When I plugged in one monitor on HDMI, it took a while but did drop back to normal CPU after resume. When I plugged in both monitors, one on HDMI one on DVI, the CPU did not return to normal (waited about 20 minutes). However, unplugging the DVI (without suspending) and waiting about five minutes, the CPU dropped back to normal.

Summary is that it appears that the high CPU on Windows Interrupts is visible for a short period after any resume (up to a few minutes) but if I have two monitors connected (I use 1 HDMI and 1 DVI) then the CPU will stay high.

  1. All non-display peripherals: After resume eventually normal CPU (~10s to few mins)
  2. All non-display plus one monitor (HDMI or DVI): After resume eventually normal CPU (few mins but it can take a long while maybe 10 or 15 mins)
  3. All non-display plus two monitors (HDMI and DVI): After resume CPU stays high
    3a. With high CPU unplug one monitor (DVI or HDMI): Eventually normal CPU (few mins)

Hope that helps. I’ll try to be a bit more prompt responding next time!


#6