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60 lines
2.8 KiB
ReStructuredText
60 lines
2.8 KiB
ReStructuredText
|kitty| 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 find
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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
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with child programs takes place in a separate thread from rendering, to improve
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smoothness.
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There are two parameters you can tune to adjust the performance. :opt:`repaint_delay`
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and :opt:`input_delay`. These control the artificial delays introduced into the
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render loop to reduce CPU usage. See :ref:`conf-kitty-performance` for details.
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See also the :opt:`sync_to_monitor` option to further decrease latency at the cost
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of some `tearing <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` which will create an executable called `kitty-profile`. Run
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that and perform the task you want to analyse, for example, scrolling a large
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file with `less`. After you quit, function call statistics will be printed to
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`stdout` and you can use tools like *kcachegrind* for more detailed analysis.
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Here are some CPU usage numbers for the task of scrolling a file continuously
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in less. The CPU usage is for the terminal process and X together and is
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measured using htop. The measurements are taken at the same font and window
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size for all terminals on a ``Intel(R) Core(TM) i7-4820K CPU @ 3.70GHz`` CPU
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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 in
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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
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deliberately throttles input parsing and output rendering to minimize
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resource usage while still being able to sink output faster than any real
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world program can produce it. Reducing CPU usage, and hence battery drain
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while achieving instant response times and smooth scrolling to a human eye
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is a far more important goal.
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