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X-HELO:	drew.franken.de
Date:	Fri, 12 Jan 2018 21:41:49 +0100
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: calloc speed difference
Message-ID:	<20180112204149.GF24623@calimero.vinschen.de>
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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 m=
ight
> >> produce misleading results due to lazy page allocation and/or zero-fil=
ling.
> >>
> >> MinGW binaries use calloc() from msvcrt.dll. This calloc() does not ca=
ll
> >> malloc() and then memset(). It directly calls:
> >>
> >>   mem =3D HeapAlloc(_crtheap, HEAP_ZERO_MEMORY, size);
> >>
> >> which possibly only reserves allocate-and-zero-fill-on-demand pages for
> >> later.
> >>
> >> Cygwin's calloc() is different.
> >=20
> > But then again, Cygwin's malloc *is* slow, particulary in
> > memory-demanding multi-threaded scenarios since that serializes all
> > malloc/free calls.
> >=20
> > 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.
> >=20
> > 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.
>=20
> 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.


Corinna

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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