Re: calloc speed difference

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

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.


Corinna

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

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