Debugging performance issues in zsh

If I add too much code in my .zshrc, my zsh takes longer to load. As I use a lot of different terminal windows (splitting one main tmux window), I want those split to happen quickly. This is why I'm trying very hard to keep the loading time of zsh under 150ms.

Hyperfine

One way to evaluate the current loading speed and track potential regressions and improvement is to use hyperfine

hyperfine --warmup 3 "zsh -i -c exit"

This will benchmark how long it will take on average to load zsh. The -i makes it load in interactive mode (so, by sourcing ~/.zshrc), and -c exit makes it execute the exit command.

Note that if you have any commands running asynchronously in the background (like prompt optimization), they will purposefuly not be included in the time.

zprof

The other debugging tool is to use zprof, which is the zsh profiler.

Include zmodload zsh/zprof at the top of your ~/.zshrc file, and zprof at the bottom. Next time you'll open zsh, you'll see a table like this:

num  calls                time                       self            name
-----------------------------------------------------------------------------------
 1)    1         240,22   240,22   65,76%    240,22   240,22   65,76%  oroshi_tools_pyenv
 2)    1          72,98    72,98   19,98%     72,98    72,98   19,98%  oroshi_theming_index
 3)    1          14,77    14,77    4,04%     14,77    14,77    4,04%  compinit
 4)    1          14,12    14,12    3,86%     14,12    14,12    3,86%  oroshi-completion-styling
 5)    1           5,85     5,85    1,60%      5,85     5,85    1,60%  oroshi_tools_fzf
 6)    1           4,95     4,95    1,35%      4,95     4,95    1,35%  _zsh_highlight_bind_widgets
 7)    1           4,56     4,56    1,25%      3,01     3,01    0,82%  oroshi_tools_z
 8)    1           2,27     2,27    0,62%      2,27     2,27    0,62%  _zsh_highlight_load_highlighters
 9)    2           2,17     1,09    0,60%      2,17     1,09    0,60%  promptinit
10)    1           2,10     2,10    0,58%      2,10     2,10    0,58%  oroshi_tools_ls
11)    7           1,51     0,22    0,41%      1,51     0,22    0,41%  add-zsh-hook
12)    7           0,64     0,09    0,17%      0,64     0,09    0,17%  compdef
13)    2           0,63     0,31    0,17%      0,63     0,31    0,17%  is-at-least
14)    1          14,85    14,85    4,07%      0,09     0,09    0,02%  oroshi_completion_compinit

This shows where most of the time is spend, the number of times a specific function is called, and if you scroll down you'll see details of the stacktrace of each sub command.

In this example, it is clear that my oroshi_tools_pyenv method is too slow, and I need to optimize it.

Note that this only tracks the time to run functions, not the time to source files, so if you need to benchmark a specific sourced file, wrap it in a function that you invoke immediatly.

Tags : #zsh

Want to add something ? Feel free to get in touch on Twitter : @pixelastic