Programming

#include <stdio.h>
char buffer[BUFSIZ]

csadev:/home/jmcnama> ll test.dat
-rwxrwxrwx   1 jmcnama    prog       164665116 Sep 18 10:36 test.dat

 
#!/bin/ksh
let i=2
while [[ $i -lt 1280000 ]]
do
    setbuf $i
    i=$(( i * 2 ))
done

#include <stdio.h>
#include <stdlib.h>
#include <sys/times.h>

clock_t get_tms(struct tms *dest)
{
	clock_t whatever=times(dest);
	return whatever;	
}

char *fmt(char *dest, struct tms *p, clock_t elapsed)
{
	int sdecimal=p->tms_stime % CLK_TCK;
	int ssec=p->tms_stime / CLK_TCK;	
	int udecimal=p->tms_utime % CLK_TCK;
	int usec=p->tms_utime / CLK_TCK;
	int edecimal=elapsed % CLK_TCK;
	int esec= elapsed / CLK_TCK;	
	sprintf(dest, "Elapsed:%3d.%02d User:%3d.%02d System:%3d.%02d",
	           esec, edecimal, usec, udecimal, ssec, sdecimal);
	return dest;           
}

void disp(int bufsiz, int cnt, struct tms *start, struct tms *end, clock_t elapsed)
{
	struct tms mytms={0,0,0,0};
	char tmp[256]={0x0};
	
	mytms.tms_utime=end->tms_utime - start->tms_utime;
	mytms.tms_stime=end->tms_stime - start->tms_stime;
	printf("Buffer: %6d Reads: %10d  ", bufsiz, cnt);
	printf("%s\n", fmt(tmp, &mytms, elapsed ));
}


int main(int argc, char **argv)
{
	int bufsz=atoi(argv[1]);
	char *buf=NULL;
	char *tmp=NULL;
	clock_t elapsed=0;
	int cnt=0;
	FILE *in=fopen("test.dat","r");
	struct tms start={0,0,0,0};
	struct tms end={0,0,0,0};
	buf=malloc(bufsz+1);
	tmp=malloc(bufsz+2);
	setvbuf(in, buf, _IOFBF, bufsz);
	elapsed=get_tms(&start);
	while(fread(tmp, bufsz, 1, in)==1) 
		cnt++;
	elapsed=get_tms(&end) - elapsed;
	disp(bufsz, cnt, &start, &end, elapsed);
	fclose(in);
	free(buf);
	free(tmp);
	return 0;	
}

csadev:/home/jmcnama> setbuf.sh                                           
Buffer:      2  Reads:   82332558  Elapsed:322.56 User: 54.99 System:258.68
Buffer:      4  Reads:   41166279  Elapsed:161.76 User: 27.83 System:129.01
Buffer:      8  Reads:   20583139  Elapsed: 81.33 User: 14.08 System: 65.79
Buffer:     16  Reads:   10291569  Elapsed: 41.06 User:  7.01 System: 33.34
Buffer:     32  Reads:    5145784  Elapsed: 20.54 User:  3.53 System: 16.70
Buffer:     64  Reads:    2572892  Elapsed: 10.52 User:  1.79 System:  8.50
Buffer:    128  Reads:    1286446  Elapsed:  5.69 User:  0.92 System:  4.44
Buffer:    256  Reads:     643223  Elapsed:  2.94 User:  0.49 System:  2.43
Buffer:    512  Reads:     321611  Elapsed:  1.64 User:  0.27 System:  1.37
Buffer:   1024  Reads:     160805  Elapsed:  0.96 User:  0.16 System:  0.79 *
Buffer:   2048  Reads:      80402  Elapsed:  0.62 User:  0.10 System:  0.52
Buffer:   4096  Reads:      40201  Elapsed:  0.38 User:  0.07 System:  0.31
Buffer:   8192  Reads:      20100  Elapsed:  0.30 User:  0.06 System:  0.24
Buffer:  16384  Reads:      10050  Elapsed:  0.27 User:  0.05 System:  0.22
Buffer:  32768  Reads:       5025  Elapsed:  0.27 User:  0.05 System:  0.22    
Buffer:  65536  Reads:       2512  Elapsed:  0.25 User:  0.05 System:  0.21
Buffer: 131072  Reads:       1256  Elapsed:  0.26 User:  0.06 System:  0.20
Buffer: 262144  Reads:        628  Elapsed:  4.21 User:  0.37 System:  0.08
Buffer: 524288  Reads:        314  Elapsed:  3.79 User:  0.42 System:  0.08
Buffer: 1048576 Reads:        157  Elapsed:  3.24 User:  0.46 System:  0.07

*BUFSIZ