tlbfaulter.c

/* 
 * tlbfaulter.c
 *
 *      This program creates an array larger than the TLB footprint,
 *      but hopefully smaller than memory.
 *      It first touches each page of the array once, which should cause
 *      each page to be loaded into memory.
 *      Then it touches the pages sequentially in a tight loop - the
 *      goal is to force the TLB to be filled quickly, so that TLB
 *      replacements will be necessary.
 *
 *      If this generates "out of memory" errors, you will need
 *      to increase the memory size of the machine (in sys161.conf)
 *      to run this test.
 */

#include <stdio.h>
#include <stdlib.h>

/* 
 * set these to match the page size of the 
 * machine and the number of entries in the TLB
 */
#define PageSize  4096
#define TLBSize     64

/* an array a bit larger than the size of the TLB footprint */
#define ArraySize ((TLBSize+5)*PageSize)
char tlbtest[ArraySize];

int
main()
{
        int i,j;

        printf("Starting the tlbfaulter program\n");

        /* load up the array */
        for (i=0; i<ArraySize; i++) {
          tlbtest[i]= 'a';
        }
        
        printf("tlbfaulter: array initialization completed\n");
        
        /* touch one array entry on each page, sequentially, 5 times */
        for(j=0; j<5; j++) {
          for (i=0; i<ArraySize; i+=PageSize) {
            tlbtest[i] += 1;
          }
        }
        
        printf("tlbfaulter: array updates completed\n");

        /* check the array values we updated */
        for (i=0; i<ArraySize; i+=PageSize) {
          if (tlbtest[i] != ('a'+5)) {
            printf("Test failed! Unexpected value at array position %d\n", i);
            return(1);
          }
        }

        printf("SUCCESS\n");
        
        return 0;
}