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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> <20180112143339 DOT GE24623 AT calimero DOT vinschen DOT de>
Reply-To:	cygwin AT cygwin DOT com
From:	cyg Simple <cygsimple AT gmail DOT com>
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Date:	Fri, 12 Jan 2018 14:59:39 -0500
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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?

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