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Port the current asciidoc documentation to sphinx
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Kovid Goyal
2018-05-29 21:03:50 +05:30
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|kitty| Performance
===================
The main goals for |kitty| performance are user perceived latency while typing
and "smoothness" while scrolling as well as CPU usage. |kitty| tries hard to find
an optimum balance for these. To that end it keeps a cache of each rendered
glyph in video RAM so that font rendering is not a bottleneck. Interaction
with child programs takes place in a separate thread from rendering, to improve
smoothness.
There are two parameters you can tune to adjust the performance. ``repaint_delay``
and ``input_delay``. These control the artificial delays introduced into the
render loop to reduce CPU usage. See |kitty.conf| for details.
See also the ``sync_to_monitor`` option to further decrease latency at the cost
of some `tearing <https://en.wikipedia.org/wiki/Screen_tearing>`_ while scrolling.
You can generate detailed per-function performance data using
`gperftools <https://github.com/gperftools/gperftools>`_. Build |kitty| with
`make profile` which will create an executable called `kitty-profile`. Run
that and perform the task you want to analyse, for example, scrolling a large
file with `less`. After you quit, function call statistics will be printed to
`stdout` and you can use tools like *kcachegrind* for more detailed analysis.
Here are some CPU usage numbers for the task of scrolling a file continuously
in less. The CPU usage is for the terminal process and X together and is
measured using htop. The measurements are taken at the same font and window
size for all terminals on a ``Intel(R) Core(TM) i7-4820K CPU @ 3.70GHz`` CPU
with a ``Advanced Micro Devices, Inc. [AMD/ATI] Cape Verde XT [Radeon HD
7770/8760 / R7 250X]`` GPU.
============== =========================
Terminal CPU usage (X + terminal)
============== =========================
|kitty| 6 - 8%
xterm 5 - 7% (but scrolling was extremely janky)
termite 10 - 13%
urxvt 12 - 14%
gnome-terminal 15 - 17%
konsole 29 - 31%
============== =========================
As you can see, |kitty| uses much less CPU than all terminals, except xterm, but
its scrolling "smoothness" is much better than that of xterm (at least to my,
admittedly biased, eyes).