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Re: calloc speed difference




On 1/12/2018 9:06 AM, Christian Franke wrote:

This variant of the above code adds one write access to each 4KiB page (guarded by "volatile" to prevent dead assignment optimization):

#include <stdio.h>
#include <stdlib.h>
#define ALLOCATION_SIZE (100 * 1024 * 1024)
int main (int argc, char *argv[]) {
     for (int i = 0; i < 1000; i++) {
         void *temp = calloc(ALLOCATION_SIZE, 1);
         if ( temp == NULL ) {
            printf("drat! calloc returned NULL\n");
            return 1;
         }
         for (int j = 0; j < ALLOCATION_SIZE; j += 4096)
           ((volatile char *)temp)[j] = (char)i;
         free(temp);
     }
     return 0;
}

Results:

Cygwin: ~310s
MinGW: ~210s

Good analysis!  There remains a lot of room for improvement, but this
shows good reasons to dig deeper to understand what goes on with large
allocations.

EM

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