GNU bug report logs - #12033
format should be faster

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: nalaginrut <nalaginrut <at> gmail.com>
Subject: bug#12033: closed (Re: bug#12033: format should be faster)
Date: Mon, 20 Aug 2012 21:52:02 +0000

[Message part 1 (text/plain, inline)]

Your bug report

#12033: format should be faster

which was filed against the guile package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 12033 <at> debbugs.gnu.org.

-- 
12033: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=12033
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: ludo <at> gnu.org (Ludovic Courtès)
To: nalaginrut <nalaginrut <at> gmail.com>
Cc: 12033-done <at> debbugs.gnu.org
Subject: Re: bug#12033: format should be faster
Date: Mon, 20 Aug 2012 23:51:38 +0200

Hi,

Here’s slightly modified code:

--8<---------------cut here---------------start------------->8---
(use-modules (ice-9 time))

(define (d len)
  (let* ((ll ((@ (srfi srfi-1) iota) len 1)) (m (1- (/ len 2))))
    (time
     (with-output-to-port (%make-void-port "w")
       (lambda ()
        (let lp ((a (list-head ll (1+ m))) (b (list-tail ll (1+ m))) (n 1))
          (and (< n len)
               (for-each (lambda (x y)
                           (display x)(display " ")(display y)
                           (display " "))
                         a b)
               (newline)
               (lp (append (list 1 (car b)) (cdr a))
                   (append (cdr b) (list (list-ref a m)))
                   (1+ n)))))))))

(define (f len)
  (let* ((ll ((@ (srfi srfi-1) iota) len 1)) (m (1- (/ len 2))))
    (time
     (with-output-to-port (%make-void-port "w")
       (lambda ()
        (let lp ((a (list-head ll (1+ m))) (b (list-tail ll (1+ m))) (n 1))
          (and (< n len)
               (for-each (lambda (x y)
                           (simple-format #t "~a ~a~%" x y))
                         a b)
               (lp (append (list 1 (car b)) (cdr a))
                   (append (cdr b) (list (list-ref a m)))
                   (1+ n)))))))))
--8<---------------cut here---------------end--------------->8---

Here’s the difference I have:

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> (f 4000)
clock utime stime cutime cstime gctime
 8.37  8.35  0.00   0.00   0.00   0.56
$9 = #f
scheme@(guile-user)> (d 4000)
clock utime stime cutime cstime gctime
 6.37  6.35  0.00   0.00   0.00   0.05
$10 = #f
--8<---------------cut here---------------end--------------->8---

So ‘simple-format’ is 30% slower than the series of ‘display’
etc. calls.

A profile from Callgrind shows that ~22% of the program with ‘f’ is
spent in ‘scm_c_substring’ and the allocations it entails.

Commit b908768a7ec79f78def344c464186a51f55b69e8 in stable-2.0 changes
the situation like this:

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> (d 4000)
clock utime stime cutime cstime gctime
 6.46  6.45  0.00   0.00   0.00   0.08
$3 = #f
scheme@(guile-user)> (f 4000)
clock utime stime cutime cstime gctime
 5.47  5.44  0.01   0.00   0.00   0.25
$4 = #f
--8<---------------cut here---------------end--------------->8---

Now, ‘simple-format’ is 15% faster than ‘display’.  Hurray!  ;-)

So, I’m closing this bug.

Note that (ice-9 format) is an order of magnitude slower, though:

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> (f 4000)
clock utime stime cutime cstime gctime
260.14 258.94  0.51   0.00   0.00  63.19
$1 = #f
--8<---------------cut here---------------end--------------->8---

Admittedly, this should be fixed, but that’s another story...

Thanks,
Ludo’.

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From: nalaginrut <nalaginrut <at> gmail.com>
To: bug-guile <at> gnu.org
Subject: format should be faster
Date: Mon, 23 Jul 2012 14:11:06 +0800

Our "format" is rather slow, can we make it faster?
I can only output strings with display if I need an faster program,
which is not so elegant.

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