When a package is loaded, and if you have use-package-verbose
set to t, or if the package takes longer than 0.1 seconds to
load, you will see a message to indicate this loading activity in the
*Messages* buffer. The same will happen for configuration, or
:config blocks, that take longer than 0.1 seconds to execute.
If you’d like to see a summary how many packages you’ve loaded, what
stage of initialization they’ve reached, and how much aggregate time
they’ve spent (roughly), you can customize the user option
use-package-compute-statistics to a non-nil value. Then
reload your packages, normally by restarting Emacs, to make sure that
use-package can gather statistics for all your packages.
Run the command M-x use-package-report to see the results. The buffer displayed is a tabulated list. To sort rows based on a particular column, move point to it and type S, or click the column name at the top of the buffer on graphical displays.
To reset all statistics that use-package has gathered for the current Emacs invocation, run the command M-x use-package-reset-statistics.
Note that if you are setting use-package-compute-statistics
directly in your init file, and not with customize, you must do
this after loading use-package, but before any
use-package forms.