Subject: 29.0.50; browse-url-emacs is extremely slow (and I think always hasbeen?)

From: Phil Sainty <[email-masked]>
Date: Thu, 06 Oct 2022 00:07:25 +1300

browse-url-emacs has always been inexplicably slow for me,
since at least Emacs 24 (but maybe just 'always').

I've just done some basic benchmarking with:

(benchmark-run (save-selected-window
                  (browse-url-emacs "http://www.example.com")))

;; If I delete the "www.example.com" buffer after each attempt, this
;; call takes nearly 3 seconds:

(2.819470404 1 0.046148434000000016)
(2.669529036 0 0.0)
(2.837350438 1 0.02421054800000011)

;; If I retain the "www.example.com" buffer, then each retry takes
;; <0.5 seconds:

(0.374270464 0 0.0)
(0.428719681 0 0.0)
(0.476068586 1 0.044311528999999794)

;; Whereas benchmarking only `url-retrieve-synchronously':

(benchmark-run (url-retrieve-synchronously "http://www.example.com"))

;; This takes <0.25 seconds.
(0.172364234 0 0.0)
(0.24314511600000002 0 0.0)
(0.19534228 0 0.0)

;; Deleting the network connection via M-x list-processes between
;; attempts adds about 0.25 seconds for all sets of benchmarks, so the
;; network connection time is not a factor.

;; eww is also fast:

(benchmark-run (save-window-excursion (let ((eww-retrieve-command 
'sync))
					(eww "http://www.example.com"))))
(0.197008672 0 0.0)
(0.25098304499999996 0 0.0)
(0.28419454299999997 0 0.0)

So something to do with browse-url-emacs is taking an additional 2.5s
on top of the basic URL request -- unless the buffer already exists,
in which case it's much faster (albeit still twice as slow as the
other options).

Presumably this could be improved?

If I benchmark-progn the final (funcall func url) in browse-url-emacs
I can see that this is where all the time is spent.  func is set to
`find-file-other-window'; so this is equivalent:

(benchmark-run
     (save-selected-window
       (let ((file-name-handler-alist
	     (cons (cons url-handler-regexp 'url-file-handler)
		   file-name-handler-alist)))
	(find-file-noselect "http://www.example.com")))
   (kill-buffer "www.example.com"))

If the buffer already existed, *Messages* says:
Contacting host: www.example.com:80
(0.408067329 0 0.0)

If the buffer did not already exist, *Messages* says:
Contacting host: www.example.com:80 [2 times]
File exists, but cannot be read
(2.617302471 0 0.0)

(The "[2 times]" is not on account of a previous test;
they are both generated by this single call.)

Benchmarking the end of `find-file-noselect' like so:

	  (benchmark-progn
	    (find-file-noselect-1 buf filename nowarn
				  rawfile truename number))

Gives me:

Elapsed time: 1.876737s (0.057295s in 1 GCs) ;; find-file-noselect-1
(2.680159853 1 0.057295379000000146)         ;; the overall 
benchmark-run

And that's as far as I've gone.

-Phil

In GNU Emacs 29.0.50 (build 4, x86_64-pc-linux-gnu, X toolkit, cairo 
version 1.15.10, Xaw scroll bars)
  of 2022-07-15 built on phil-lp
Repository revision: 00eb894a56d63fad3573a53dd57c323289711512
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 
11.0.12008000
System Description: Ubuntu 18.04.6 LTS

Configured using:
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