[okular] [Bug 399208] Okular has an extemely high latency when scrolling with a wacom tablet

[Keziolio]

https://bugs.kde.org/show_bug.cgi?id=399208

--- Comment #3 from Keziolio <keziolio123 at gmail.com> ---
I compiled okular 1.1.3 and 1.0.3 and the problem was still present, I'm pretty
sure that the regression was more recent than that...

So where should I look?

I haven't noticed this kind of slowdown in other parts of the system, there's
something that breaks okular in a specific way...


I think the problem can be worked around by consuming the input as fast as
possible and updating the page position once every screen refresh, I can mind a
bad framerate but not 30+ seconds of latency, I think this is still an okular
issue, but I was not even able to find the relevant file/function in the okular
source code and it's not that well documented, if someone can help in that
regard that'll be great



This is the output of perf top when the latency is rolling:

Samples: 347K of event 'cycles:ppp', 4000 Hz, Event count (approx.):
74074580252
Overhead  Shared Object                            Symbol
  34.75%  [kernel]                                 [k]
copy_user_enhanced_fast_string
   3.13%  [kernel]                                 [k] __check_object_size      
   1.64%  libc-2.28.so                             [.]
__memmove_avx_unaligned_erms
   1.38%  [kernel]                                 [k] __radix_tree_lookup      
   1.03%  perf                                     [.] hpp__sort_overhead

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