bug#73766: 30.0.91; (documentation 'pcase) can take several seconds

bug#73766: 30.0.91; (documentation 'pcase) can take several seconds

[Yikai Zhao]

When `lsp-mode` is loaded, `(documentation 'pcase)` can take several
seconds to complete.

Apparently, it would iterate over all defined pcase macros (N), and for
each of those, `help-fns-short-filename` would iterate over all items in
`load-path` (M). Total time complexity is N*M.

In my case, N is about ~400 (defined in lsp-protocols.el) and M is about
~100 (I think it's a normal case?).

This is especially problematic since the `documentation` method can be
invoked by eldoc, which affects the responsiveness during editing.

--

Here's my profiler result:

        2713  86% - timer-event-handler
        2713  86%  - apply
        2707  86%   - #<native-comp-function
F616e6f6e796d6f75732d6c616d626461_anonymous_lambda_12>
        2707  86%    - eldoc-print-current-symbol-info
        2707  86%     - eldoc--invoke-strategy
        2707  86%      - eldoc-documentation-default
        2707  86%       - #<native-comp-function
F616e6f6e796d6f75732d6c616d626461_anonymous_lambda_17>
        2707  86%        - elisp-eldoc-funcall
        2707  86%         - elisp-get-fnsym-args-string
        2707  86%          - documentation
        2707  86%           - pcase--make-docstring
        2606  82%            - help-fns-short-filename
        2598  82%             - file-relative-name
         335  10%                file-remote-p
          27   0%                string-prefix-p

--

In GNU Emacs 30.0.91 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.22.30, cairo version 1.15.10) of 2024-09-12 built on 8afcf8f014b8
Repository revision: 9a1c76bf7ff49d886cc8e1a3f360d71e62544802
Repository branch: HEAD
Windowing system distributor 'The X.Org Foundation', version 11.0.12101004
System Description: Ubuntu 22.04.5 LTS

Configured using:
 'configure --prefix=/work/dist/AppDir --disable-locallisppath
 --with-native-compilation=aot --with-json --with-threads --with-sqlite3
 --with-tree-sitter --with-dbus --with-xml2 --with-modules --with-libgmp
 --with-gpm --with-lcms2 --with-mps --with-x --without-pgtk
 --without-gconf --with-x-toolkit=gtk3 --with-xft --without-tiff
 --without-imagemagick --with-gif --with-png --with-rsvg --with-webp
 --with-harfbuzz --with-cairo --with-libotf --without-m17n-flt
 --with-jpeg emacs_cv_jpeglib=/usr/lib/x86_64-linux-gnu/libjpeg.a
 CPPFLAGS=-I/work/dist/AppDir/include LDFLAGS=-L/work/dist/AppDir/lib'

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG LCMS2
LIBOTF LIBXML2 MODULES NATIVE_COMP NOTIFY INOTIFY PDUMPER PNG RSVG
SECCOMP SOUND SQLITE3 THREADS TOOLKIT_SCROLL_BARS TREE_SITTER WEBP X11
XDBE XIM XINPUT2 XPM GTK3 ZLIB

Important settings:
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  value of $EMACSDOC: /tmp/.mount_emacsXLI1Nd/share/emacs/30.0.91/etc
  value of $EMACSLOADPATH: /tmp/.mount_emacsXLI1Nd/share/emacs/30.0.91/lisp
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/tmp/.mount_emacsXLI1Nd/libexec/emacs/30.0.91/x86_64-pc-linux-gnu
  value of $LC_MONETARY: en_US.UTF-8
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  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=fcitx
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Major mode: ELisp/l

Minor modes in effect:
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Load-path shadows:
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/home/yikai/.emacs.d/lib/use-package/use-package-core hides
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/home/yikai/.emacs.d/lib/compat/compat hides
/tmp/.mount_emacsXLI1Nd/share/emacs/30.0.91/lisp/emacs-lisp/compat

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evil-collection-view view jka-compr evil-collection-woman woman
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jsonnet-mode smie conf-mode url-queue textsec uni-scripts idna-mapping
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threads dbusbind inotify lcms2 dynamic-setting system-font-setting
font-render-setting cairo gtk x-toolkit xinput2 x multi-tty move-toolbar
make-network-process native-compile emacs)

Memory information:
((conses 16 1185831 1011558) (symbols 48 67125 23)
 (strings 32 316477 39434) (string-bytes 1 10307989)
 (vectors 16 123279) (vector-slots 8 2358285 658163)
 (floats 8 1093 15048) (intervals 56 31071 5410) (buffers 992 56))

bug#73766: 30.0.91; (documentation 'pcase) can take several seconds

[Eli Zaretskii]

> From: Yikai Zhao <yikai@z1k.dev>
> Date: Sat, 12 Oct 2024 16:02:04 +0800
> 
> When `lsp-mode` is loaded, `(documentation 'pcase)` can take several
> seconds to complete.
> 
> Apparently, it would iterate over all defined pcase macros (N), and for
> each of those, `help-fns-short-filename` would iterate over all items in
> `load-path` (M). Total time complexity is N*M.
> 
> In my case, N is about ~400 (defined in lsp-protocols.el) and M is about
> ~100 (I think it's a normal case?).
> 
> This is especially problematic since the `documentation` method can be
> invoked by eldoc, which affects the responsiveness during editing.
> 
> --
> 
> Here's my profiler result:
> 
>         2713  86% - timer-event-handler
>         2713  86%  - apply
>         2707  86%   - #<native-comp-function
> F616e6f6e796d6f75732d6c616d626461_anonymous_lambda_12>
>         2707  86%    - eldoc-print-current-symbol-info
>         2707  86%     - eldoc--invoke-strategy
>         2707  86%      - eldoc-documentation-default
>         2707  86%       - #<native-comp-function
> F616e6f6e796d6f75732d6c616d626461_anonymous_lambda_17>
>         2707  86%        - elisp-eldoc-funcall
>         2707  86%         - elisp-get-fnsym-args-string
>         2707  86%          - documentation
>         2707  86%           - pcase--make-docstring
>         2606  82%            - help-fns-short-filename
>         2598  82%             - file-relative-name
>          335  10%                file-remote-p
>           27   0%                string-prefix-p

Adding Stefan and João, in case they have some comments or
suggestions.

bug#73766: 30.0.91; (documentation 'pcase) can take several seconds

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

[-- Attachment #1: Type: text/plain, Size: 343 bytes --]

>> Apparently, it would iterate over all defined pcase macros (N), and for
>> each of those, `help-fns-short-filename` would iterate over all items in
>> `load-path` (M). Total time complexity is N*M.
> Adding Stefan and João, in case they have some comments or
> suggestions.

How 'bout a patch like the one below?


        Stefan

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: shortenfile.patch --]
[-- Type: text/x-diff, Size: 2067 bytes --]

diff --git a/lisp/help-fns.el b/lisp/help-fns.el
index 3f64b2e126f..3e0973c25ee 100644
--- a/lisp/help-fns.el
+++ b/lisp/help-fns.el
@@ -1090,17 +1090,38 @@ help-fns--mention-shortdoc-groups
         (fill-region-as-paragraph (point-min) (point-max))
         (goto-char (point-max))))))
 
+(require 'radix-tree)
+
+(defconst help-fns--radix-trees
+  (make-hash-table :weakness 'key :test #'equal))
+
+(defun help-fns--radix-tree (dirs)
+  (with-memoization (gethash dirs help-fns--radix-trees)
+    (let ((rt radix-tree-empty))
+      (dolist (d dirs)
+        (let ((d (abbreviate-file-name
+                  (file-name-as-directory (expand-file-name d)))))
+          (setq rt (radix-tree-insert rt d t))))
+      rt)))
+
 (defun help-fns-short-filename (filename)
-  (let* ((abbrev (abbreviate-file-name filename))
-         (short abbrev))
-    (dolist (dir load-path)
-      (let ((rel (file-relative-name filename dir)))
-        (if (< (length rel) (length short))
-            (setq short rel)))
-      (let ((rel (file-relative-name abbrev dir)))
-        (if (< (length rel) (length short))
-            (setq short rel))))
-    short))
+  (let* ((short (abbreviate-file-name (expand-file-name filename)))
+         (dir (file-name-directory short))
+         (nondir (file-name-nondirectory short))
+         (rt (help-fns--radix-tree load-path))
+         (prefixes (radix-tree-prefixes rt dir)))
+    (if (not prefixes)
+        ;; The file is not inside the `load-path'.
+        ;; FIXME: We used to try and shorten it with "../".
+        ;; (dolist (dir load-path)
+        ;;   (let ((rel (file-relative-name filename dir)))
+        ;;     (if (< (length rel) (length short))
+        ;;         (setq short rel)))
+        ;;   (let ((rel (file-relative-name abbrev dir)))
+        ;;     (if (< (length rel) (length short))
+        ;;         (setq short rel))))
+        short
+      (file-relative-name short (caar prefixes)))))
 
 (defun help-fns--analyze-function (function)
   ;; FIXME: Document/explain the differences between FUNCTION,

bug#73766: 30.0.91; (documentation 'pcase) can take several seconds

[Yikai Zhao]

On Sun, Oct 13, 2024 at 12:39 AM Stefan Monnier
<monnier@iro.umontreal.ca> wrote:
>
> >> Apparently, it would iterate over all defined pcase macros (N), and for
> >> each of those, `help-fns-short-filename` would iterate over all items in
> >> `load-path` (M). Total time complexity is N*M.
> > Adding Stefan and João, in case they have some comments or
> > suggestions.
>
> How 'bout a patch like the one below?

Hello,

I tried this patch and can confirm it improves the performance.
Here's the result of (benchmark-run (documentation 'pcase)):

- master: 4s
- master with this patch: 0.12s

However it's still slower than last stable version:
- 29.4 version: 0.02s



Yikai

bug#73766: 30.0.91; (documentation 'pcase) can take several seconds

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

>> >> Apparently, it would iterate over all defined pcase macros (N), and for
>> >> each of those, `help-fns-short-filename` would iterate over all items in
>> >> `load-path` (M). Total time complexity is N*M.
>> > Adding Stefan and João, in case they have some comments or
>> > suggestions.
>> How 'bout a patch like the one below?
> I tried this patch and can confirm it improves the performance.
> Here's the result of (benchmark-run (documentation 'pcase)):
> - master: 4s
> - master with this patch: 0.12s

Thanks 🙂

Wli, this is a non-trivial chunk of code and it's used more often than
just to get the docstring of `pcase`, so I'm clearly not obviously safe
for `emacs-30`.

Here are some options I can think of:

- Install it `emacs-30` anyway.
- Revert on `emacs-30` the change that introduced the slowdown:

    commit 052c2ce0284c5193c9d6768a45a9b3508af51230
    Author: Stefan Monnier <monnier@iro.umontreal.ca>
    Date:   Sun Feb 11 17:43:37 2024 -0500

        (pcase): Add buttons to the macros' defs in the docstring of `pcase`

        * lisp/emacs-lisp/pcase.el (pcase--find-macro-def-regexp): New var.
        (find-function-regexp-alist): Add entry for `pcase-macro`s.
        (help-fns--signature): Move declaration to where we know it is valid.
        (pcase--make-docstring): Add buttons to jump to the definition
        of Pcase macros.

- Install on `emacs-30` a simpler and more focused change, which should
  work acceptably in most cases, such as:

    diff --git a/lisp/emacs-lisp/pcase.el b/lisp/emacs-lisp/pcase.el
    index 5a7f3995311..811d42793cd 100644
    --- a/lisp/emacs-lisp/pcase.el
    +++ b/lisp/emacs-lisp/pcase.el
    @@ -214,7 +214,7 @@ pcase--make-docstring
                   (save-excursion
                     (forward-char -1)
                     (insert (format-message "  in `"))
    -                (help-insert-xref-button (help-fns-short-filename filename)
    +                (help-insert-xref-button (file-name-nondirectory filename)
                                              'help-function-def symbol filename
                                              'pcase-macro)
                     (insert (format-message "'."))))

> However it's still slower than last stable version:
> - 29.4 version: 0.02s

Slower than 29.4 is expected because it gives more information (the
file name, as a hyperlink).
I think for `C-h o` this plenty fast.

There's still a remaining performance issue for things like
`eldoc-mode`, admittedly where we'd really want it to be instantaneous,
but I think this should be fixed by making `eldoc` call `documentation`
in a special way to skips those useless computations (eldoc just wants
a "short doc" anyway).  This affects other functions using the
`function-documentation` property in a similar way.


        Stefan

bug#73766: 30.0.91; (documentation 'pcase) can take several seconds

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> Wli, this is a non-trivial chunk of code and it's used more often than
  ^^^
  Eli

Boy, my typing is getting worse by the day.  Sometimes I wonder is my
brain is turning to mush.  At least for the above blunder, `e` is right
next to `w` on my keyboard, so there is some kind of "logic" to it.


        Stefan

bug#73766: 30.0.91; (documentation 'pcase) can take several seconds

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Eli Zaretskii <eliz@gnu.org>,  João Távora
>  <joaotavora@gmail.com>,
>   73766@debbugs.gnu.org
> Date: Thu, 17 Oct 2024 21:22:58 -0400
> 
> > Wli, this is a non-trivial chunk of code and it's used more often than
>   ^^^
>   Eli
> 
> Boy, my typing is getting worse by the day.  Sometimes I wonder is my
> brain is turning to mush.  At least for the above blunder, `e` is right
> next to `w` on my keyboard, so there is some kind of "logic" to it.

Your simple cypher was successfully decoded here ;-)

bug#73766: 30.0.91; (documentation 'pcase) can take several seconds

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Eli Zaretskii <eliz@gnu.org>,  João Távora
>  <joaotavora@gmail.com>,
>   73766@debbugs.gnu.org
> Date: Thu, 17 Oct 2024 13:22:00 -0400
> 
> Eli, this is a non-trivial chunk of code and it's used more often than
> just to get the docstring of `pcase`, so I'm clearly not obviously safe
> for `emacs-30`.
> 
> Here are some options I can think of:
> 
> - Install it `emacs-30` anyway.
> - Revert on `emacs-30` the change that introduced the slowdown:
> 
>     commit 052c2ce0284c5193c9d6768a45a9b3508af51230
>     Author: Stefan Monnier <monnier@iro.umontreal.ca>
>     Date:   Sun Feb 11 17:43:37 2024 -0500
> 
>         (pcase): Add buttons to the macros' defs in the docstring of `pcase`
> 
>         * lisp/emacs-lisp/pcase.el (pcase--find-macro-def-regexp): New var.
>         (find-function-regexp-alist): Add entry for `pcase-macro`s.
>         (help-fns--signature): Move declaration to where we know it is valid.
>         (pcase--make-docstring): Add buttons to jump to the definition
>         of Pcase macros.
> 
> - Install on `emacs-30` a simpler and more focused change, which should
>   work acceptably in most cases, such as:
> 
>     diff --git a/lisp/emacs-lisp/pcase.el b/lisp/emacs-lisp/pcase.el
>     index 5a7f3995311..811d42793cd 100644
>     --- a/lisp/emacs-lisp/pcase.el
>     +++ b/lisp/emacs-lisp/pcase.el
>     @@ -214,7 +214,7 @@ pcase--make-docstring
>                    (save-excursion
>                      (forward-char -1)
>                      (insert (format-message "  in `"))
>     -                (help-insert-xref-button (help-fns-short-filename filename)
>     +                (help-insert-xref-button (file-name-nondirectory filename)
>                                               'help-function-def symbol filename
>                                               'pcase-macro)
>                      (insert (format-message "'."))))

I'd prefer the last alternative for emacs-30, but then you say:

> There's still a remaining performance issue for things like
> `eldoc-mode`, admittedly where we'd really want it to be instantaneous,
> but I think this should be fixed by making `eldoc` call `documentation`
> in a special way to skips those useless computations (eldoc just wants
> a "short doc" anyway).  This affects other functions using the
> `function-documentation` property in a similar way.

Does it mean that this slowdown of eldoc was also caused by commit
052c2ce0284c5193c9d6768a45a9b3508af51230, and if so, does the patch
you've shown previously (and which you consider not safe enough for
emacs-30) solve the eldoc slowdown as well?