From: Eliot Moss <moss@cs.umass.edu>
To: cygwin@cygwin.com
Subject: Re: calloc speed difference
Date: Fri, 12 Jan 2018 22:00:00 -0000 [thread overview]
Message-ID: <caeb25e5-a89d-d6b3-f0e0-2efcf28fb84b@cs.umass.edu> (raw)
In-Reply-To: <46515148-9f8e-6eae-69f9-9bf20921097a@t-online.de>
On 1/12/2018 9:06 AM, Christian Franke wrote:
> This variant of the above code adds one write access to each 4KiB page (guarded by "volatile" to
> prevent dead assignment optimization):
>
> #include <stdio.h>
> #include <stdlib.h>
> #define ALLOCATION_SIZE (100 * 1024 * 1024)
> int main (int argc, char *argv[]) {
> Â Â Â for (int i = 0; i < 1000; i++) {
> Â Â Â Â Â Â Â void *temp = calloc(ALLOCATION_SIZE, 1);
> Â Â Â Â Â Â Â if ( temp == NULL ) {
> Â Â Â Â Â Â Â Â Â Â printf("drat! calloc returned NULL\n");
> Â Â Â Â Â Â Â Â Â Â return 1;
> Â Â Â Â Â Â Â }
> Â Â Â Â Â Â Â for (int j = 0; j < ALLOCATION_SIZE; j += 4096)
> Â Â Â Â Â Â Â Â Â ((volatile char *)temp)[j] = (char)i;
> Â Â Â Â Â Â Â free(temp);
> Â Â Â }
> Â Â Â return 0;
> }
>
> Results:
>
> Cygwin: ~310s
> MinGW: ~210s
Good analysis! There remains a lot of room for improvement, but this
shows good reasons to dig deeper to understand what goes on with large
allocations.
EM
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next prev parent reply other threads:[~2018-01-12 22:00 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-12 7:19 Lee
2018-01-12 8:38 ` Eliot Moss
2018-01-12 9:07 ` Marco Atzeri
2018-01-12 10:52 ` Lee
2018-01-21 11:01 ` Marco Atzeri
2018-01-12 14:05 ` Christian Franke
2018-01-12 14:33 ` Corinna Vinschen
2018-01-12 19:59 ` cyg Simple
2018-01-12 20:07 ` cyg Simple
2018-01-12 20:41 ` Corinna Vinschen
2018-01-12 22:34 ` cyg Simple
2018-01-13 10:48 ` Lee
2018-01-13 10:04 ` Lee
2018-01-12 22:00 ` Eliot Moss [this message]
2018-01-13 8:35 ` Lee
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