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Subject: Re: calloc speed difference
To: cygwin AT cygwin DOT com
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Reply-To: cygwin AT cygwin DOT com
From: cyg Simple <cygsimple AT gmail DOT com>
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Date: Fri, 12 Jan 2018 15:06:56 -0500
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On 1/12/2018 2:59 PM, cyg Simple wrote:
> On 1/12/2018 9:33 AM, Corinna Vinschen wrote:
>> On Jan 12 15:06, Christian Franke wrote:
>>> Lee wrote:
>>>> Why is the cygwin gcc calloc so much slower than the
>>>> i686-w64-mingw32-gcc calloc?
>>>>    1:12 vs 0:11
>>>>
>>>> $cat calloc-test.c
>>>> #include <stdio.h>
>>>> #include <stdlib.h>
>>>> #define ALLOCATION_SIZE (100 * 1024 * 1024)
>>>> int main (int argc, char *argv[]) {
>>>>      for (int i = 0; i < 10000; i++) {
>>>>          void *temp = calloc(ALLOCATION_SIZE, 1);
>>>>          if ( temp == NULL ) {
>>>>             printf("drat! calloc returned NULL\n");
>>>>             return 1;
>>>>          }
>>>>          free(temp);
>>>>      }
>>>>      return 0;
>>>> }
>>>>
>>>
>>> Could reproduce the difference on an older i7-2600K machine:
>>>
>>> Cygwin: ~20s
>>> MinGW: ~4s
>>>
>>> Timing [cm]alloc() calls without actually using the allocated memory might
>>> produce misleading results due to lazy page allocation and/or zero-filling.
>>>
>>> MinGW binaries use calloc() from msvcrt.dll. This calloc() does not call
>>> malloc() and then memset(). It directly calls:
>>>
>>>   mem = HeapAlloc(_crtheap, HEAP_ZERO_MEMORY, size);
>>>
>>> which possibly only reserves allocate-and-zero-fill-on-demand pages for
>>> later.
>>>
>>> Cygwin's calloc() is different.
>>
>> But then again, Cygwin's malloc *is* slow, particulary in
>> memory-demanding multi-threaded scenarios since that serializes all
>> malloc/free calls.
>>
>> The memory handling within Cygwin is tricky.  Attempts to replace good
>> old dlmalloc with a fresher jemalloc or ptmalloc failed, but that only
>> means the developer (i.e., me, in case of ptmalloc) was too lazy...
>> busy! I mean busy... to pull this through.
>>
>> Having said that, if somebody would like to take a stab at replacing
>> dlmalloc with something leaner, I would be very happy and assist as
>> much as I can.
> 
> Corina, how reliable is the Cygwin time function on a non-Cygwin
> executable?  Isn't this a comparison of apples to oranges?
> 

s/Corina/Corinna

Sorry,
-- 
cyg Simple

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