[Emacs] Add startup time and uptime logging for Emacs

org/config/emacs.org

@@ -249,6 +249,28 @@ files by default.
       auto-save-default t)
 #+end_src
 
+I’m also interested in keeping track of how fast Emacs loads on my
+computer, as well as for how long I keep it open. The values are
+stored in a ~.csv~ with three columns:
+- The date when Emacs was closed
+- Emacs’ init time
+- Emacs’ uptime
+#+begin_src emacs-lisp
+(defvar my/emacs-log-file-time (expand-file-name "emacs-time.csv" user-emacs-directory))
+
+(defun my/write-emacs-loadtime-and-uptime ()
+  (with-temp-buffer
+    (find-file my/emacs-log-file-time)
+    (goto-char (point-max))
+    (insert (format "%s,%s,%s\n"
+                    (string-trim (shell-command-to-string "date +%F-%H-%M-%S"))
+                    (emacs-init-time "%f")
+                    (emacs-uptime "%dd %hh %mm %ss")))
+    (save-buffer)))
+
+(add-to-list 'kill-emacs-hook #'my/write-emacs-loadtime-and-uptime)
+#+end_src
+
 #+begin_src emacs-lisp
 (setq window-combination-resize t) ; take new window space from all other windows
 #+end_src