Table of

8.1.2010The year I started blogging (blogware)
9.1.2010Linux initramfs with iSCSI and bonding support for PXE booting
9.1.2010Using manually tweaked PTX assembly in your CUDA 2 program
9.1.2010OpenCL autoconf m4 macro
9.1.2010Mandelbrot with MPI
10.1.2010Using dynamic libraries for modular client threads
11.1.2010Creating an OpenGL 3 context with GLX
11.1.2010Creating a double buffered X window with the DBE X extension
12.1.2010A simple random file read benchmark
14.12.2011Change local passwords via RoundCube safer
5.1.2012Multi-GPU CUDA stress test
6.1.2012CUDA (Driver API) + nvcc autoconf macro
29.5.2012CUDA (or OpenGL) video capture in Linux
31.7.2012GPGPU abstraction framework (CUDA/OpenCL + OpenGL)
7.8.2012OpenGL (4.3) compute shader example
10.12.2012GPGPU face-off: K20 vs 7970 vs GTX680 vs M2050 vs GTX580
4.8.2013DAViCal with Windows Phone 8 GDR2
5.5.2015Sample pattern generator


A simple random file read benchmark

I have been mostly using iozone for benchmarking my file systems, but it isn't really a file system benchmark as much as it is a disk benchmark. One night I was after a random read test with randomized files to benchmark an upgrade I had gotten to my Solaris ZFS file system. The closest benchmark iozone had to this was the one where a big file is written, and accessed randomly.

Now, file systems have been complicated (or smart) enough for ages for a test like this not to tell you all about how fast your storage system is accessing random files. For example, ZFS's raidz1/2 use stripe sizes that dynamically adjust to file sizes. Reading one massive file a small piece here, a small piece there will not produce the same kind of load as accessing real individual files. And this is an important task, since most system data is - actually - piles and piles of small files.

I know there are an abundance of better benchmark suites out there which simulate this kind of load, but I just wanted to write this small piece of software myself since I knew exactly what I was after.

So, here it is. It prints out a help with -h, but the parameters you need to know are

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <sys/time.h>

#define MAXREAD 1024*1024 // We don't read more than 1MB in one call

// Simple timing
struct timeval t_start, t_end;
void starttime() {
    gettimeofday(&t_start, NULL);
void gettime_r(char* desc, int repeat) {
    gettimeofday(&t_end, NULL);        
    long int timedif = (long int)((t_end.tv_sec*1e6 + t_end.tv_usec) -
        (t_start.tv_sec*1e6 + t_start.tv_usec));
    printf("%s time: %.3f, average: %.4f\n", desc, (double)timedif/1e6f, (double)timedif/1e6f/(double)repeat);
void gettime(char* desc) { gettime_r(desc, 1); }

int main(int argc, char **argv) {
    // Setting some defaults
    int64_t filesize = 4096;
    int count = 10;
    float loop = 1.0f;
    int rvalue;
    int debug = 0;
    unsigned char *data = (unsigned char*)malloc(MAXREAD);
    while ((rvalue = getopt(argc, argv, "h--s:n:l:d")) != -1)
        switch (rvalue) {
            case 'h':
                printf("Usage: %s [-h] [-s filesize] [-n filecount] [-l loopcount (float)] [-d]\n",
            case 's':
                sscanf(optarg, "%ld", &filesize);
                if (filesize < 0 || filesize > 1e12) { // 0 .. 1 terabyte
                    fprintf(stderr, "Filesize of %ld bytes is out of bounds, resetting to 4096\n", filesize);
                    filesize = 4096;
            case 'n':
                sscanf(optarg, "%d", &count);
                if (count < 0 || count > 1e9) { // 0 .. 1 billion
                    fprintf(stderr, "Count out of bounds, resetting to 10\n", count);
                    count = 10;
            case 'l':
                sscanf(optarg, "%f", &loop);
                if (loop < 0.0f || loop > (float)1e6) { // 0 .. 1 million
                    fprintf(stderr, "Loop out of bounds, resetting to 1.0\n", count);
                    loop = 1.0f;
            case 'd':
                debug = 1;

    printf("Creating %d files of size %Ld B", count, filesize);
    printf(", total data %.2f MB\n", (double)(filesize*count)/(1024.0*1024.0));

    char filename[1024];
    for (int i = 0; i < MAXREAD && i < filesize; ++i)
        data[i] = i%256;
    for (int i = 0; i < count; ++i) {
        sprintf(filename, "rand%09d", i);
        if (debug) printf("Creating file %s\n", filename);
        FILE *f = fopen(filename, "w");
        // Full 1MB blocks
        int64_t left = filesize;
        while (left > MAXREAD) {
            if (debug) printf("\twriting %d bytes\n", MAXREAD);
            fwrite(data, sizeof(char), MAXREAD, f);
            left -= MAXREAD;
        if (left) {
            if (debug) printf("\twriting %d bytes\n", left);
            fwrite(data, sizeof(char), left, f);
        left = 0;

    for (double i = 0.0; i < (double)count*loop; ++i) {
        int index = rand()%count;
        sprintf(filename, "rand%09d", index);
        if (debug)
            printf("Loop %d/%d: opening file %s\n",
                (int)i, (int)((double)count*loop), filename);
        FILE *f = fopen(filename, "r");
        int64_t left = filesize;
        while (left > MAXREAD) {
            if (debug) printf("\treading %d bytes\n", MAXREAD);
            fread(data, sizeof(char), MAXREAD, f);
            left -= MAXREAD;
        if (left) {
            if (debug) printf("\treading %d bytes\n", left);
            fread(data, sizeof(char), left, f);
        left = 0;
    gettime_r("File read", (int)loop);

    for (int i = 0; i < count; ++i) {
        sprintf(filename, "rand%09d", i);


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