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13303416b8
Add more text roles and links. Fix typos. Adjust the default shortcut order in overview. Notes on the impact of kitty-open.desktop on the default open apps. Document KITTY_DEVELOP_FROM in glossary. Add Python type hints to the watcher example. Mention clone-in-kitty in launch --copy-env. Fix remote control ls example does not work, by escaping the backslash.
61 lines
2.8 KiB
ReStructuredText
61 lines
2.8 KiB
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Performance
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===================
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The main goals for |kitty| performance are user perceived latency while typing
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and "smoothness" while scrolling as well as CPU usage. |kitty| tries hard to
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find an optimum balance for these. To that end it keeps a cache of each rendered
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glyph in video RAM so that font rendering is not a bottleneck. Interaction with
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child programs takes place in a separate thread from rendering, to improve
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smoothness.
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There are two config options you can tune to adjust the performance,
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:opt:`repaint_delay` and :opt:`input_delay`. These control the artificial delays
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introduced into the render loop to reduce CPU usage. See
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:ref:`conf-kitty-performance` for details. See also the :opt:`sync_to_monitor`
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option to further decrease latency at the cost of some `screen tearing
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<https://en.wikipedia.org/wiki/Screen_tearing>`__ while scrolling.
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You can generate detailed per-function performance data using
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`gperftools <https://github.com/gperftools/gperftools>`__. Build |kitty| with
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``make profile``. Run kitty and perform the task you want to analyse, for
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example, scrolling a large file with :program:`less`. After you quit, function
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call statistics will be printed to STDOUT and you can use tools like
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*KCachegrind* for more detailed analysis.
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Here are some CPU usage numbers for the task of scrolling a file continuously in
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:program:`less`. The CPU usage is for the terminal process and X together and is
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measured using :program:`htop`. The measurements are taken at the same font and
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window size for all terminals on a ``Intel(R) Core(TM) i7-4820K CPU @ 3.70GHz``
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CPU with a ``Advanced Micro Devices, Inc. [AMD/ATI] Cape Verde XT [Radeon HD
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7770/8760 / R7 250X]`` GPU.
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============== =========================
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Terminal CPU usage (X + terminal)
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============== =========================
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|kitty| 6 - 8%
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xterm 5 - 7% (but scrolling was extremely janky)
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termite 10 - 13%
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urxvt 12 - 14%
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gnome-terminal 15 - 17%
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konsole 29 - 31%
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============== =========================
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As you can see, |kitty| uses much less CPU than all terminals, except xterm, but
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its scrolling "smoothness" is much better than that of xterm (at least to my,
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admittedly biased, eyes).
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.. _perf-cat:
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.. note::
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Some people have asked why kitty does not perform better than terminal XXX
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in the test of sinking large amounts of data, such as catting a large text
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file. The answer is because this is not a goal for kitty. kitty deliberately
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throttles input parsing and output rendering to minimize resource usage
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while still being able to sink output faster than any real world program can
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produce it. Reducing CPU usage, and hence battery drain while achieving
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instant response times and smooth scrolling to a human eye is a far more
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important goal.
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