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#define _GNU_SOURCE
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdint.h>
#include <time.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h> // strlen()
#define GiB 1024l*1024l*1024l
#define s2ns(s) ((s)*1000l*1000l*1000l)
int seq_walk(char* mem, int len, char to_find) {
int num_42 = 0;
// Stride of 4096 bytes (one 4k page)
for (int i = 4096; i < len; i += 4096)
if (mem[i] == to_find)
num_42++;
return num_42;
}
long time_diff_ns(struct timespec start, struct timespec stop) {
return (s2ns(stop.tv_sec) + stop.tv_nsec) - (s2ns(start.tv_sec) + start.tv_nsec);
}
// TODO: take *num_42, return time
//#define PAGED_FILE "/home/jbakita/1gib_random_f"
#define PAGED_FILE "/dev/nvme0n1"
int main(int argc, char **argv) {
int iters = 1;
int no_seq = 0;
if (argc > 1)
iters = atoi(argv[1]);
if (argc > 2) {
no_seq = strncmp(argv[2], "--no-seq", strlen(argv[2])) ? 1 : 0;
fprintf(stderr, "Skipping seq, but using no-seq emulation with demand paging\n");
}
struct timespec start, stop, seq_stop;
int clear_fd = open("/proc/sys/vm/drop_caches", O_WRONLY);
if (clear_fd == -1) {
perror("Unable to open /proc/sys/vm/drop_caches");
return 1;
}
char clear_cmd = '3';
for (int i = 0; i < iters; i++) {
int fd = open(PAGED_FILE, O_RDWR);
if (fd == -1) {
perror("Unable to open " PAGED_FILE);
return 1;
}
// Clear page cache
write(clear_fd, &clear_cmd, 1);
// VIA MMAP
clock_gettime(CLOCK_MONOTONIC_RAW, &start);
char* mem = mmap(NULL, GiB, PROT_READ, MAP_PRIVATE, fd, 0);
if (mem == MAP_FAILED) {
perror("Unable to mmap " PAGED_FILE);
return 1;
}
// Fault on all the pages via a sequential walk
int num_42 = seq_walk(mem, GiB, 42);
clock_gettime(CLOCK_MONOTONIC_RAW, &stop);
int num_52 = 0;
if (no_seq)
num_52 = seq_walk(mem, GiB, 52);
clock_gettime(CLOCK_MONOTONIC_RAW, &seq_stop);
if (num_52)
fprintf(stderr, "Something is seriously wrong! Found a 52 in a buffer that should be only 42s\n");
long duration = (s2ns(stop.tv_sec) + stop.tv_nsec) - (s2ns(start.tv_sec) + start.tv_nsec);
// Emulate the time demand paging would take if we didn't have to walk
if (no_seq) {
long seq_time = time_diff_ns(stop, seq_stop);
duration -= seq_time;
}
if (iters == 1) {
printf("Took %ldus via mmap\n", duration / 1000);
printf("Read %d 42s of %ld expected\n", num_42, GiB/4096);
} else {
printf("%ld, ", duration / 1000);
}
munmap(mem, GiB);
close(fd);
}
if (iters > 1)
printf("\n");
for (int i = 0; i < iters; i++) {
char* mem;
int fd = open(PAGED_FILE, O_RDWR | O_DIRECT);
if (fd == -1) {
perror("Unable to open " PAGED_FILE);
return 1;
}
// Clear page cache
write(clear_fd, &clear_cmd, 1);
// VIA READ
clock_gettime(CLOCK_MONOTONIC_RAW, &start);
// Aligned malloc(GiB) basicially
int res = posix_memalign((void**)&mem, 4096, GiB);
if (res) {
fprintf(stderr, "posix_memalign() failure. Error %d.", res);
return 1;
}
res = read(fd, mem, GiB);
if (res == -1) {
perror("Unable to read 1GiB from /dev/nvme0n1");
return 1;
}
if (res < GiB) {
fprintf(stderr, "Unable to read the buffer all at once!");
return 2;
}
int num_42 = 0;
if (!no_seq)
num_42 = seq_walk(mem, GiB, 42); // Not strictly necessary, but to match mmap path overheads
clock_gettime(CLOCK_MONOTONIC_RAW, &stop);
if (iters == 1) {
printf("Took %ldus via read\n", ((s2ns(stop.tv_sec) + stop.tv_nsec) - (s2ns(start.tv_sec) + start.tv_nsec)) / 1000);
if (!no_seq)
printf("Read %d 42s of %ld expected\n", num_42, GiB/4096);
} else {
printf("%ld, ", ((s2ns(stop.tv_sec) + stop.tv_nsec) - (s2ns(start.tv_sec) + start.tv_nsec)) / 1000);
}
close(fd);
free(mem);
}
if (iters > 1)
printf("\n");
return 0;
}
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