Hello, I am using Fedora 28 KDE Spin on my ASUS laptop with a Nvidia Graphics Card and it was working pretty well (for a couple of months) until this morning

It has started lagging, jittering and being unresponsive in general, several restarts and updating didn't do any good either. Moving program windows is hard and using Plasma is almost impossible now... the start menu, context menu on the desktop etc. are all very laggy.

My CPU usage is also constantly around 20-30% when idle now, it used to be 0-2% before! After searching around I found a few threads but none of them were able to offer a proper solution

This thread looks very relevant (also this).

I do not recall doing any action which might affect KDE/Plasma the night before.

Can anyone help me solve this issue? Thank you in advance!

I just did a little test, I logged in as another user in a different virtual terminal and started plasma in it, the desktop there seems to be much more usable, the remaining lag is caused by the already increased CPU usage from my original user I reckon.

After some interesting conversations on IRC I managed to use perf to analyse the performance, here is my report:

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Samples: 3K of event 'cycles:uppp', Event count (approx.): 1209136066
  Children      Self  Command          Shared Object                                  Symbol                              ◆
+   15.94%     0.70%  plasmashell      [nf_defrag_ipv4]                               [k] nf_defrag_ipv4_enable           ▒
+    7.17%     0.23%  QSGRenderThread  [nf_defrag_ipv4]                               [k] nf_defrag_ipv4_enable           ▒
+    4.88%     0.00%  plasmashell      [unknown]                                      [.] 0xe9097400287f8348              ▒
+    4.45%     4.45%  plasmashell      libc-2.27.so                                   [.] _int_malloc                     ▒
+    2.75%     2.75%  plasmashell      libc-2.27.so                                   [.] _int_free                       ▒
+    2.40%     2.40%  plasmashell      libc-2.27.so                                   [.] malloc                          ▒
+    2.14%     2.14%  plasmashell      libQt5Core.so.5.10.1                           [.] 0x000000000027f611              ▒
+    2.12%     0.00%  QDBusConnection  [nf_defrag_ipv4]                               [k] nf_defrag_ipv4_enable           ▒
+    1.90%     1.90%  plasmashell      libQt5Core.so.5.10.1                           [.] QIODevicePrivate::read          ▒
+    1.36%     0.00%  QSGRenderThread  [unknown]                                      [.] 0xe9097400287f8348              ▒
+    1.29%     0.00%  plasmashell      libQt5Core.so.5.10.1                           [.] QBuffer::qt_metacast            ▒
+    1.28%     0.00%  plasmashell      [unknown]                                      [.] 0x795711b46caf1c00              ▒
+    1.26%     0.00%  plasmashell      libQt5Core.so.5.10.1                           [.] 0x0000000000328520              ▒
+    1.24%     1.24%  plasmashell      libQt5Core.so.5.10.1                           [.] QBuffer::readData               ▒
+    1.24%     0.00%  plasmashell      [unknown]                                      [.] 0x0000556f4cc960a0              ▒
+    1.07%     0.95%  plasmashell      libQt5Core.so.5.10.1                           [.] QArrayData::allocate            ▒
+    0.89%     0.89%  plasmashell      libc-2.27.so                                   [.] malloc_consolidate              ▒
+    0.73%     0.00%  QSGRenderThread  [unknown]                                      [k] 0x6f69746300000000              ▒
+    0.73%     0.00%  QSGRenderThread  libQt5Quick.so.5.10.1                          [.] QSGAbstractRenderer::qt_metacast▒
     0.70%     0.70%  plasmashell      libc-2.27.so                                   [.] __memmove_avx_unaligned_erms    ▒
+    0.65%     0.00%  QXcbEventReader  [unknown]                                      [.] 0x0000556f4b3cb170              ▒
+    0.61%     0.00%  plasmashell      libQt5Core.so.5.10.1                           [.] 0x00000000003e4720              ▒
     0.60%     0.60%  plasmashell      libc-2.27.so                                   [.] cfree@GLIBC_2.2.5               ▒
     0.60%     0.60%  QDBusConnection  libc-2.27.so                                   [.] malloc                          ▒
+    0.60%     0.00%  plasmashell      [unknown]                                      [.] 0x4810c0834800262d              ▒
+    0.60%     0.00%  plasmashell      [unknown]                                      [.] 0x0000556f0000007a              ▒
+    0.60%     0.00%  plasmashell      [unknown]                                      [.] 0x00007fe70ebc0d60              ▒
+    0.59%     0.00%  plasmashell      [unknown]                                      [.] 0xa78d4c54410028ff              ▒


Apparently the calls to nf_defrag_ipv4_enable are taking quite a chunk of CPU.. I am not sure though, I have never used perf before and all of this has been suggested by a user from IRC. I will look more into this.

Edit: I am willing to share my .data file so that you can look at the perf report. Please let me know if you need it You can download it from here.

After more searching and prodding around, I found out that perf report was giving me a red herring i.e misleading information

I worked with a user on IRC to figure that out, then I left my laptop running for a while and when I came back, kactivity manager was crashing every few minutes consistently, to my luck another user had the same problem and the helper also advised me to delete the content inside this directory while logged out:

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~/.local/share/kactivitymanagerd/resources/

Thanks to tosky (the helper) for fixing the issue