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@jsteemann
Created January 30, 2018 11:40
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quick test program to assess disk write performance with and without fdatasync
/*
write performance test
tests disk write performance with and without fdatasync
will write a configurable amount of 1MB data blocks to disk
and then optionally call fdatasync after each
usage:
compile with
gcc -O3 -Wall -Wextra -std=c11 test-write-performance.c
and then run with
time ./a.out /tmp/out 1000 0
or
time ./a.out /tmp/out 1000 1
The invocation parameters are:
- output file (make sure to use an outfile on the disk of interest)
- number of 1MB blocks to write
- use fdatasync (0 = off, 1 = on)
*/
#define _POSIX_C_SOURCE 200112L
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#define MB (1024ULL * 1024ULL)
int main(int argc, char* argv[]) {
if (argc < 4) {
fprintf(stderr, "usage: %s outfile mb sync\n", argv[0]);
exit(1);
}
char const* outfile = argv[1];
int mb = atoi(argv[2]);
if (mb < 0) {
fprintf(stderr, "usage: %s outfile mb sync\n", argv[0]);
exit(1);
}
int sync = atoi(argv[3]);
if (sync != 0 && sync != 1) {
fprintf(stderr, "usage: %s outfile mb sync\n", argv[0]);
exit(1);
}
char block[MB]; // 1 mb;
memset(&block[0], 0xa5, sizeof(block));
FILE* fp = fopen(outfile, "w");
if (fp == NULL) {
fprintf(stderr, "error while opening file: %s\n", strerror(errno));
exit(1);
}
int fd = fileno(fp);
if (fd < 0) {
fprintf(stderr, "error determining file descriptor\n");
exit(1);
}
fprintf(stdout, "about to write %llu bytes to %s %s sync\n", (unsigned long long) (mb * MB), outfile, sync ? "with" : "without");
int total = 0;
for (int i = 0; i < mb; ++i) {
size_t written = fwrite(&block[0], sizeof(block), 1, fp);
if (ferror(fp) != 0) {
fprintf(stderr, "file output error\n");
exit(1);
}
if (sync) {
if (fdatasync(fd) == -1) {
fprintf(stderr, "error while syncing file: %s\n", strerror(errno));
exit(1);
}
}
total += written;
fprintf(stdout, "written %llu bytes of %llu\n", (unsigned long long) (total * MB), (unsigned long long) (mb * MB));
}
fclose(fp);
return 0;
}
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