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I'm using Kubuntu 17.04, KDE Frameworks: 5.37.0., kernel 4.10.0-35-generic.

All applications (Firefox, Yakuake, System Settings, Digikam, LibreOffice, Kate, NetBeans) are exhibiting strange pauses/lagging/faltering/stops when scrolling content with the mouse wheel -- mouse is wireless Logitech M185.

What might be causing this? How can I debug it?

For example when scrolling my Yakuake terminal content each 3rd and 4th scroll are ineffective and don't move the content. The content can be scrolled as fast as one wishes by dragging the scrollbar or by middle-click scrolling.

Ksysguard shows no log entries appearing, nor any noticeable resource changes happening when I'm doing this. It doesn't matter how many apps are open the scrolling "lags" in the same way. Even when I scroll at one "bump" of the mousewheel each second the lag/pause still happens; a series of moves being ineffective.

I even tried doing two scrolls, turning the mouse off-and-on, but the pauses come in the same place as if they're a property of the page being scrolled.

The same pausing happens when altering spin box values using the mouse.

Where to start?

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    I this issue related to mouse (you can scroll smoothly with keyboard), or with graphics (no smooth scrolling anywhere)? What graphics card/driver do you have? – Ott Toomet Sep 25 '17 at 22:51
  • Like I mentioned, I can drag the scrollbar up and down with mouse without any lagging; keyboard scroll is normal (keyboard -- Logitech K270 -- is part of same wireless set, uses same receiver. Graphics is "Kaveri" on an AMD A8-7600, Radeon R7, 8G ram using stock open source amdgpu driver (~40FPS on CS:GO). Middle-click on Google SERPs will give very smooth autoscroll at any speed one chooses. The scrolling is smooth, it just doesn't respond to the scroll wheel every couple of turns; it's more of a failure to respond than a lag. – pbhj Sep 26 '17 at 20:07
  • Ah ... looking at this again I think it might be the rotary encoder in the mouse itself, I was assuming a software fault. – pbhj Sep 26 '17 at 20:11
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The rotary encoder was faulty, it needed cleaning.

On the M185 Logitech mouse the encoder uses a spoked wheel passing a EM emitter of some form (can't tell what exactly). With dust/crud clogging the spokes the sensor doesn't see the rotation of the wheel.

Remove screw from under battery location. Pull top of mouse back to release plastic locating lugs. Clean mouse wheel (I rinsed under water, be sure to completely dry before reassembly; compressed air would be better). Reassemble.

Scroll now working.

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