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test-tlb.c
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test-tlb.c
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#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/time.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdarg.h>
#include <stdlib.h>
#include <limits.h>
#include <errno.h>
#include <signal.h>
#include <math.h>
#include <time.h>
#define PAGE_SIZE 4096
#define FREQ 3.9
static int test_hugepage = 0;
static int random_list = 0;
static void die(const char *fmt, ...)
{
va_list argp;
va_start(argp, fmt);
vfprintf(stderr, fmt, argp);
va_end(argp);
fputc('\n', stderr);
exit(1);
}
static volatile int stop = 0;
void alarm_handler(int sig)
{
stop = 1;
}
unsigned long usec_diff(struct timeval *a, struct timeval *b)
{
unsigned long usec;
usec = (b->tv_sec - a->tv_sec)*1000000;
usec += b->tv_usec - a->tv_usec;
return usec;
}
/*
* Warmup run.
*
* This is mainly to make sure that we can go around the
* map without timing any writeback activity from the cache
* from creating the map.
*/
static unsigned long warmup(void *map)
{
unsigned int offset = 0;
struct timeval start, end;
gettimeofday(&start, NULL);
do {
offset = *(volatile unsigned int *)(map + offset);
} while (offset);
gettimeofday(&end, NULL);
return usec_diff(&start, &end);
}
static double do_test(void *map)
{
unsigned long count = 0, offset = 0, usec;
struct timeval start, end;
struct itimerval itval = {
.it_interval = { 0, 0 },
.it_value = { 0, 0 },
};
/*
* Do one run without counting, and make sure we can do
* at least five runs, and have at least about 0.2s of
* timing granularity (0.2s selected randomly to make the
* run-of-five take 1s in the fast case).
*/
usec = warmup(map) * 5;
if (usec < 200000)
usec = 200000;
itval.it_value.tv_sec = usec / 1000000;
itval.it_value.tv_usec = usec % 1000000;
stop = 0;
signal(SIGALRM, alarm_handler);
setitimer(ITIMER_REAL, &itval, NULL);
gettimeofday(&start, NULL);
do {
count++;
offset = *(unsigned int *)(map + offset);
} while (!stop);
gettimeofday(&end, NULL);
usec = usec_diff(&start, &end);
// Make sure the compiler doesn't compile away offset
*(volatile unsigned int *)(map + offset);
// return cycle time in ns
return 1000 * (double) usec / count;
}
static unsigned long get_num(const char *str)
{
char *end, c;
unsigned long val;
if (!str)
return 0;
val = strtoul(str, &end, 0);
if (!val || val == ULONG_MAX)
return 0;
while ((c = *end++) != 0) {
switch (c) {
case 'k':
val <<= 10;
break;
case 'M':
val <<= 20;
break;
case 'G':
val <<= 30;
break;
default:
return 0;
}
}
return val;
}
static void randomize_map(void *map, unsigned long size, unsigned long stride)
{
unsigned long off;
unsigned int *lastpos, *rnd;
int n;
rnd = calloc(size / stride + 1, sizeof(unsigned int));
if (!rnd)
die("out of memory");
/* Create sorted list of offsets */
for (n = 0, off = 0; off < size; n++, off += stride)
rnd[n] = off;
/* Randomize the offsets */
for (n = 0, off = 0; off < size; n++, off += stride) {
unsigned int m = (unsigned long)random() % (size / stride);
unsigned int tmp = rnd[n];
rnd[n] = rnd[m];
rnd[m] = tmp;
}
/* Create a circular list from the random offsets */
lastpos = map;
for (n = 0, off = 0; off < size; n++, off += stride) {
lastpos = map + rnd[n];
*lastpos = rnd[n+1];
}
*lastpos = rnd[0];
free(rnd);
}
// Hugepage size
#define HUGEPAGE (2*1024*1024)
static void *create_map(void *map, unsigned long size, unsigned long stride)
{
unsigned int flags = MAP_PRIVATE | MAP_ANONYMOUS;
unsigned long off, mapsize;
unsigned int *lastpos;
/*
* If we're using hugepages, we will just re-use any existing
* hugepage map - the issues with different physical page
* allocations for cache associativity testing just isn't worth
* it with large pages.
*
* With regular pages, just mmap over the old allocation to
* force new page allocations. Hopefully this will then make
* the virtual mapping different enough to matter for timings.
*/
if (map) {
if (test_hugepage)
return map;
flags |= MAP_FIXED;
}
mapsize = size;
if (test_hugepage)
mapsize += 2*HUGEPAGE;
map = mmap(map, mapsize, PROT_READ | PROT_WRITE, flags, -1, 0);
if (map == MAP_FAILED)
die("mmap failed");
if (test_hugepage) {
unsigned long mapstart = (unsigned long) map;
mapstart += HUGEPAGE-1;
mapstart &= ~(HUGEPAGE-1);
map = (void *)mapstart;
mapsize = size + HUGEPAGE-1;
mapsize &= ~(HUGEPAGE-1);
madvise(map, mapsize, MADV_HUGEPAGE);
} else {
/*
* Christian Borntraeger tested on an s390, and had
* transparent hugepages set to "always", which meant
* that the small-page case never triggered at all
* unless you explicitly ask for it.
*/
madvise(map, mapsize, MADV_NOHUGEPAGE);
}
lastpos = map;
for (off = 0; off < size; off += stride) {
lastpos = map + off;
*lastpos = off + stride;
}
*lastpos = 0;
return map;
}
int main(int argc, char **argv)
{
unsigned long stride, size;
const char *arg;
void *map;
double cycles;
srandom(time(NULL));
while ((arg = argv[1]) != NULL) {
if (*arg != '-')
break;
for (;;) {
switch (*++arg) {
case 0:
break;
case 'H':
test_hugepage = 1;
continue;
case 'r':
random_list = 1;
continue;
default:
die("Unknown flag '%s'", arg);
}
break;
}
argv++;
}
size = get_num(argv[1]);
stride = get_num(argv[2]);
if (stride < 4 || size < stride)
die("bad arguments: test-tlb [-H] <size> <stride>");
map = NULL;
cycles = 1e10;
for (int i = 0; i < 5; i++) {
double d;
map = create_map(map, size, stride);
if (random_list)
randomize_map(map, size, stride);
d = do_test(map);
if (d < cycles)
cycles = d;
}
printf("%6.2fns (~%.1f cycles)\n",
cycles, cycles*FREQ);
return 0;
}