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Subject: |
format should be faster |
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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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--- Begin Message ---
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Subject: |
Re: bug#12033: format should be faster |
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Date: |
Mon, 20 Aug 2012 23:51:38 +0200 |
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User-agent: |
Gnus/5.130005 (Ma Gnus v0.5) Emacs/24.1 (gnu/linux) |
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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