/*
 * write-bench.c
 *
 * test write-performance to a device for n loops, designed for
 * testing to a raw device where the underlying physical device has
 * caching turned off
 *
 * cw@f00f.org --- Mon Jul 16 04:21:12 NZST 2001
 *
 * USE AT YOUR OWN RISK! NO WARRANTY GIVEN OR IMPLIED
 */

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
/* #include <publib.h> */

/* XXX edit for your CPU */
const float MHz = 860.947 * 1000 * 1000;

/* some kind of 64-bit tsc is required */
#ifdef __i386__
#define rdtsc(low,high) \
    __asm__ __volatile__("rdtsc" : "=a" (low), "=d" (high))
#else /* __i386__ */
#error "Please define rdtsc(low32,high32) for your architecture"
#endif /* __i386__ */


int main(int argc,char *argv[])
{
    const int secsize = 512;
    int f, i, loops;
    char *buf;
    double sum = 0.0, sumsq = 0.0, duration;
    union jack {
        unsigned int l[2];
        unsigned long long v;
    }before_io, after_io;

    if(argc != 3){
        fprintf(stderr,"please supply two arguments; "
                "the device and the number of loops\n");
        return 2;
    }

    loops = atoi(argv[2]);

    if(!(buf = malloc(secsize))){
        perror("malloc");
        return 1;
    }
    if(((long)buf) % secsize){
        free(buf);
        if(!(buf = malloc(secsize*2 - 1))){
            perror("malloc");
            return 1;
        }
        (long)buf = ((long)buf + secsize - 1) & ~(secsize - 1);
    }
    /* memfill(buf, secsize, "wibble", 6); */
    memset(buf, 'r', secsize);

    if(-1 == (f = open(argv[1], O_RDWR))){
        perror("open");
        return 1;
    }

    rdtsc(before_io.l[0],before_io.l[1]);
    for(i=0;i<loops;++i){
#ifdef PWRITE_WORKS
        if(-1 == pwrite(f, buf, secsize, 0)){
            perror("pwrite");
            return 1;
        }
#else /* PWRITE_WORKS */
        if(-1 == lseek(f, 0, SEEK_SET)){
            perror("lseek");
            return 1;
        }
        if(-1 == write(f, buf, secsize)){
            perror("write");
            return 1;
        }
#endif /* PWRITE_WORKS */
        rdtsc(after_io.l[0],after_io.l[1]);

        duration = (after_io.v - before_io.v) / MHz;
        sum += duration;
        sumsq += duration * duration;

        before_io.v = after_io.v;
    }

    printf("Loops              %-8d\n", loops);
    printf("Total time taken   %-8.4f s\n", sum);
    printf("Average write time %-8.4f ms\n", 1000.0 * sum / loops);
    printf("  (std. dev)       %-8f ms\n", 1000.0 * sqrt(sumsq - sum*sum/loops) / (loops - 1));
    printf("Writes/second      %-8.4f s^-1\n", loops / sum);

    return 0;
}