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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> <b7ab3fe3-fa81-432d-33ad-9c0d7948b044 AT gmail DOT com> <20180112204149 DOT GF24623 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 17:34:19 -0500
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On 1/12/2018 3:41 PM, Corinna Vinschen wrote:
> On Jan 12 14:59, cyg Simple wrote:
>> On 1/12/2018 9:33 AM, Corinna Vinschen wrote:
>>> On Jan 12 15:06, Christian Franke wrote:
>>>> 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?
> 
> I wasn't comparing, in fact.  I was just saying that Cygwin's malloc
> is slow, partially because dlmalloc is not the fastest one, partially
> due to the serialization overhead in multithreading scenarios.

No, but the OP *is* doing a compare.  From what I remember doing a time
comparison of a non-Cygwin app compared to a Cygwin app isn't really a
logical comparison.  Even if the two were a Cygwin app multiple runs of
the same app will show variance.

-- 
cyg Simple

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