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Posting-Version: version B 2.10.1 6/24/83; site mh3bs.UUCP
Path: utzoo!linus!security!genrad!mit-eddie!mit-vax!eagle!mh3bs!agp
From: agp@mh3bs.UUCP
Newsgroups: net.unix-wizards
Subject: Re: m and n of mkfs
Message-ID: <354@mh3bs.UUCP>
Date: Sat, 19-Nov-83 10:45:58 EST
Article-I.D.: mh3bs.354
Posted: Sat Nov 19 10:45:58 1983
Date-Received: Mon, 21-Nov-83 01:15:23 EST
References: <298@bunker.UUCP>
Organization: Bell Labs, Murray Hill, NJ
Lines: 101

A few USENIX conferences ago, someone presented a
paper on computing optimal magic numbers for a
cpu/disk pair.  For what it is worth, I will post
their program here:

#include	<stdio.h>

#define	SECTORS	(disk[n].d_sec_tk * disk[n].d_surf)

struct	cpu
{
	char	*cpu_name;
	int	Bps;
};

struct	cpu	cpu[] =
{
	"PDP23",	119,
	"pdp23",	119,
	"11/23",	119,
	"23",		119,
	"PDP34",	119,
	"pdp34",	119,
	"11/34",	119,
	"34",		119,
	"PDP45",	170,
	"pdp45",	170,
	"11/45",	170,
	"45",		170,
	"PDP70",	210,
	"pdp70",	210,
	"11/70",	210,
	"70",		210,
	"VAX780",	210,
	"vax780",	210,
	"11/780",	210,
	"780",		210,
	"VAX",		210,
	"vax",		210,
	NULL,		NULL
};

struct	disk
{
	char	*d_name;
	int	d_spin;
	int	d_sec_tk;
	int	d_byte_bk;
	int	d_surf;
	int	d_cyl;
	int	d_tk_seek;
	int	d_avg_seek;
};

struct disk	disk[] =
{
/*       disk   spin   sec_tk byte_blk surf     cyl   tk_seek  avg_seek  */
	"rk05",	1500,	12,	512,	2,	203,	10,	50,
	"rl01",	2400,	20,	256,	2,	256,	15,	55,
	"rp03",	2400,	10,	512,	20,	406,	8,	29,
	"rp04",	3600,	22,	512,	19,	411,	7,	28,
	"rp05",	3600,	22,	512,	19,	411,	6,	29,
	"rp06",	3600,	22,	512,	19,	815,	6,	29,
	NULL,	NULL,	NULL,	NULL,	NULL,	NULL,	NULL,	NULL
};

main(argc,argv)
char	**argv;
{
	register int	k, n, i;
	int	block, speed;
	int	f_n;

	for(k=0; cpu[k].cpu_name[0] != NULL; ++k) {
		if(strcmp(argv[1],cpu[k].cpu_name) == 0) break;
	}

	if(cpu[k].Bps == NULL) {
		printf("unknown cpu: %s\n",argv[1]);
		exit(1);
	}

	for(n=0; disk[n].d_name[0] != NULL; ++n) {

		block=((disk[n].d_spin/10)*disk[n].d_sec_tk);
		speed=((60*(cpu[k].Bps + 1))/10);

		for(i=1; i <= disk[n].d_surf; ++i) {
			f_n = SECTORS / i;
			if(f_n >= 100) continue;
			if((SECTORS % i) == 0) {
				if((f_n % disk[n].d_sec_tk) == 0) break;
			}
			break;
		}
		printf("%s:  %d / %d",
			disk[n].d_name,
			(block / speed) + 1, SECTORS);
		printf("\n");
	}
}