X-Recipient:	archive-cygwin AT delorie DOT com
DomainKey-Signature:	a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id
	:list-unsubscribe:list-subscribe:list-archive:list-post
	:list-help:sender:reply-to:subject:to:references:from:message-id
	:date:mime-version:in-reply-to:content-type
	:content-transfer-encoding; q=dns; s=default; b=rPdNP1wbmHmpa2kr
	ul8kDWAvqwjR/EsCg/4Ft44Rev8ry316JjjgFQqz2Xo1DIUzMaZAJGG1Oa0xm7Fr
	qYnxnkbRPRWnnsAQ/SsJagIafI4Gzgc5kcwImN9GhRMMNvjr26Fn38mVWWPwzpx0
	2fE+gGP7JGgb0bIdxHSYax0Uzzk=
DKIM-Signature:	v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id
	:list-unsubscribe:list-subscribe:list-archive:list-post
	:list-help:sender:reply-to:subject:to:references:from:message-id
	:date:mime-version:in-reply-to:content-type
	:content-transfer-encoding; s=default; bh=NX/w5cdvr414aljFiK8/pj
	og+fI=; b=vT0CssMW7rNPIUIgV41tppWdINWtrdDPossXn0SVGHxn7m8mgz6TIy
	8xCkiUR1V7fMiNiAUf3Zy3XXbxWog03M0DQJZq9/kKR/b1LDRoosyvMsjxV79h6l
	PvyFeceeMeGpra1KQca6R5VnOfkzLQiBVf86f00Aafq75Am2y7E9E=
Mailing-List:	contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Id:	<cygwin.cygwin.com>
List-Subscribe:	<mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive:	<http://sourceware.org/ml/cygwin/>
List-Post:	<mailto:cygwin AT cygwin DOT com>
List-Help:	<mailto:cygwin-help AT cygwin DOT com>, <http://sourceware.org/ml/#faqs>
Sender:	cygwin-owner AT cygwin DOT com
Mail-Followup-To:	cygwin AT cygwin DOT com
Delivered-To:	mailing list cygwin AT cygwin DOT com
Authentication-Results:	sourceware.org; auth=none
X-Virus-Found:	No
X-Spam-SWARE-Status:	No, score=-2.6 required=5.0 tests=BAYES_00,RCVD_IN_DNSWL_LOW,SPF_PASS,T_RP_MATCHES_RCVD autolearn=ham version=3.3.2 spammy=210s, 310s, HContent-Transfer-Encoding:8bit
X-HELO:	mailsrv.cs.umass.edu
Reply-To:	moss AT cs DOT umass DOT edu
Subject:	Re: calloc speed difference
To:	cygwin AT cygwin DOT com
References:	<CAD8GWsvxzFe0dPnxO-odTY+EG5XOAApLjcOSN5d7vXhtLW0GmQ AT mail DOT gmail DOT com> <46515148-9f8e-6eae-69f9-9bf20921097a AT t-online DOT de>
From:	Eliot Moss <moss AT cs DOT umass DOT edu>
Message-ID:	<caeb25e5-a89d-d6b3-f0e0-2efcf28fb84b@cs.umass.edu>
Date:	Fri, 12 Jan 2018 17:00:24 -0500
User-Agent:	Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2
MIME-Version:	1.0
In-Reply-To:	<46515148-9f8e-6eae-69f9-9bf20921097a@t-online.de>
X-IsSubscribed:	yes
Note-from-DJ:	This may be spam

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[]) {
>      for (int i = 0; i < 1000; i++) {
>          void *temp = calloc(ALLOCATION_SIZE, 1);
>          if ( temp == NULL ) {
>             printf("drat! calloc returned NULL\n");
>             return 1;
>          }
>          for (int j = 0; j < ALLOCATION_SIZE; j += 4096)
>            ((volatile char *)temp)[j] = (char)i;
>          free(temp);
>      }
>      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

--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple

- Raw text -