Just upgraded from xenial to bionic. Kubuntu plasma.
$ uname -a
Linux 4.13.0-25-generic #29-Ubuntu SMP Mon Jan 8 21:14:41 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

Now video playback is choppy, so is playing games. Every couple of seconds I get a delay of almost a second.

Is the i915 the correct driver to be using for the Intel E3-1200 v3/4th gen?

$ lsmod | grep video
uvcvideo 90112 0
videobuf2_vmalloc 16384 1 uvcvideo
videobuf2_memops 16384 1 videobuf2_vmalloc
videobuf2_v4l2 24576 1 uvcvideo
videobuf2_core 40960 2 uvcvideo,videobuf2_v4l2
videodev 176128 3 uvcvideo,videobuf2_core,videobuf2_v4l2
media 40960 2 uvcvideo,videodev
video 40960 2 asus_wmi,i915

$ lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics Controller (rev 06)

Kubuntu Bionic (18.04) is still under development and won't be released until April.

You can expect bugs and unusual behaviour if you run a development version, and you should report any such irregularities to the developers of Kubuntu.

^ this.

the generic advice is:

- open top and see if something is eating resources
- look at lspci output if your graphics slipped into fallback mode

You weren't kidding about bionic still under development. 2 days later and 100+ package updates later, the issue no longer seems to be happening now.

And it may even reappear at some point before development is complete. That's the nature of the roller-coaster ride that can be experienced running a version still under development.

You may want to mark the thread as "Solved" (see "Thread Tools" at the top of the thread). Cheers.