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Re: Some thoughts about Emacs performance

From: Robert Boyer
Subject: Re: Some thoughts about Emacs performance
Date: Fri, 16 Feb 2024 10:15:04 -0600

Dear Simon,

That's the kindest message I have ever received.  Thank you so very much.  Made my day and my life.

I am hoping, using 'native-compile', about which I have heard great things, to contribute one function that is the same as 'stable-sort' in Common Lisp.  It runs, in SBCL, about twice as fast as SBCL's stable-sort.  See the attached file n3ms.lisp. The really stunning news to me is that my friend Grant Passmore, running on an M3 machine only yesterday, and taking advantage of threads in SBCL, saw a 5x performance improvement over SBCL's stable-sort.  I have not the slightest clue about whether threads are in Emacs or in its future.

The name of my function is 'msa'. I have attached the file msa.el in its current state of development. It is far from finished and no one in their right mind will try to use it!  But great Emacs minds might read it and tell me things I need to know.

The threads code I added to 'msa' for SBCL is I think an amazing comment upon what a fantastic job the SBCL folks have done for threads.  My addition to 'msa' to take advantage of threads is only about a dozen lines long, and in my extremely unhumble opinion, it is a dozen lines of the greatest beauty that I have ever seen. May the Lord bless John von Neumann, wherever he is, for 'merge-sort'.

But I do fear for the worst.  I am 77 and have always worried too much,  I also attach a file that I just sent to rms, because I cannot yet use m-x report-emacs-bug, due to some mailer problem.  I run on a $100 Lenovo Chromebook, and somehow, by magic Emacs 28 just suddenly appeared a few days ago and it is great, except for 1. some mailer problem with report-emacs-bug and 2. crucial to my work on msa, the following bug report, in the attached file compile-bug.el, on native-compile.

I say I fear for the worst because if that bug is what I think it is, it would kill 'msa' performance.
Very secondarily, even if the bug is fixed, I have no idea how I could ever take advantage of it!
Emacs 28 appeared by magic on my Chromebook only a few days ago.  I have always depended upon the kindness of friends and strangers, who have magically installed Emacs for me.  All I did to install Emacs on my Chromebook was to run this command:

   sudo apt-get install emacs

Great minds, I guess you guys with Emacs, at Google, and at Debian should know that is all I know and all I need to know, so far, about installing Emacs.

Thanks so very, very much for your extremely kind letter,


P. S.  You mention 'random'.  My bet is that unless you fix the bug that I mention above, no one could ever do a random via native-compiler that would be competitive.  Using declared fixnum and vectors is crucial to any speed-competitive work on 'random' that I can imagine.

P. P. S. My home phone is 512 467 0182. Phone me any time.  You or anyone else doing Emacs development. If you like, since I can call anywhere in the USA for free, I will hang up and call you right back if you prefer.

P. P. P. S.  You kindly mentioned the ancient 'boyer' benchmark.  One must know about it that it has a bug, as far as truth rather than performance testing, is concerned.  Whoever translated that file from Maclisp to Common Lisp failed to note that 'member' now needs a :test 'equal bit in the call.
Common Lisp defaults the test to 'eql, and that is not what one needs.  Anyway, that code is only for performance testing.  Nqthm and ACL2 are real theorem-proving programs written in Common Lisp and they are both easy to obtain for 'free', or for 'gratis', as rms is now saying.  To some I guess, 
'free' may sometimes have a bad connotation; not for me, though.  May the Free Software Foundation forever flourish.  What Harvard has done for us all: Gates, Zuckerberg, Stallman.

On Fri, Feb 16, 2024 at 8:08 AM Simon Leinen <simon.leinen@gmail.com> wrote:

welcome to the emacs-devel list, and thanks a lot for *your* wonderful
contributions (theorem prover, string search, and Lisp benchmarking -
I remember boyer.lisp from RPG's reference work[1]).

On Thu, Feb 8, 2024 at 8:15 AM Robert Boyer
<robertstephenboyer@gmail.com> wrote:
> Emacs 27.1 has a 'sort' function that takes longer than stable-sort of SBCL. Maybe
> by a factor of 2. See also my attached file 'ms.lisp'.
> There may be a lot that can be improved in Emacs'
> handling of cl-loop, setf, elt, or cl-random.

In this case, cl-random seems to be the main culprit for the slow
initialization—replacing that with plain "random" speeds it up by
about a factor of ten.  There was some discussion on the list recently
about cl-random vs. random. The main functional difference is that
cl-random supports a defined state. But the performance difference may
be due more to the fact that random is written in C, and cl-random in

As for the sorting itself, both Emacs and SBCL seem to use mergesort
in their implementations of (stable-)sort.  Emacs's implementation is
written in C, SBCL's in Lisp. Performance is quite similar—on my
system (Apple Macbook Air M2) Emacs takes about 35% longer to sort a
million random numbers than SBCL.  (On the other hand when sorting it
again, i.e. when the vector is already fully sorter, Emacs is quite a
bit faster than SBCL—maybe Emacs chose to optimize for partly-sorted
vectors at the expense of a bit of performance for random input.)

In general, the Emacs Lisp runtime system and compiler(s) aren't as
optimized as SBCL for general Lisp use.  But it gets quite close!

On the other hand, Emacs has editor-specific code (e.g. redisplay) and
data structures (e.g. buffers) which are highly optimized and partly
written in C.  But it doesn't try to be a standalone platform for
performance-oriented Lisp developers.  Of course Emacs is very
suitable as a Software Development Environment for systems such as
SBCL, and there are many good integration options—personally I use the
SLIME package these days.

Best regards, and enjoy Lisping in Emacs!

> ;; First some Emacs, with times on my $100 Chromebook.
> (setq n 6)
> (defun make-random-array (n)
>   (let ((a (make-vector n 0)))
>     (cl-loop for i below n do
>              (setf (elt a i) (cl-random 1000000)))
>     a))
> (byte-compile 'make-random-array)
> (benchmark '(setq foo (make-random-array (expt 10 n))) 1) -- 2.3 seconds
> (benchmark '(sort foo '<) 1) -- 1 second
> ;; Second some Common Lisp, with times for SBCL on my $100 Chromebook.
> (defparameter n 6)
> (defun make-random-array (n)
>   (declare (fixnum n))
>   (let ((a (make-array n)))
>     (declare (type array a))
>     (loop for i fixnum below n do
>           (setf (aref a i) (random most-positive-fixnum)))
>     a))
> (time (defparameter foo (make-random-array (expt 10 n))))  -- .041 seconds
> (time (progn (stable-sort foo '<) nil)) -- .45 seconds
> Thanks so much for Emacs, which is so great that I cannot put it
> into words.
> Bob

[1] https://dreamsongs.com/Files/Timrep.pdf

Attachment: msa.el
Description: Binary data

Attachment: compile-bug.el
Description: Binary data

Attachment: n3ms.lisp
Description: application/lisp

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