usr/src/usr.bin/w/proc_compare.c

/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * %sccs.include.redist.c%
 */

#ifndef lint
static char sccsid[] = "@(#)proc_compare.c      5.5 (Berkeley) %G%";
#endif /* not lint */

/*
 * Returns 1 if p2 is more active than p1
 *
 * The algorithm for picking the "more active" process is thus:
 *
 *      1) Runnable processes are favored over anything
 *         else.  The runner with the highest cpu
 *         utilization is picked (p_cpu).  Ties are
 *         broken by picking the highest pid.
 *      2) Next, the sleeper with the shortest sleep
 *         time is favored.  With ties, we pick out
 *         just short-term sleepers (p_pri <= PZERO).
 *         Further ties are broken by picking the highest
 *         pid.
 *
 *      NOTE - if you change this, be sure to consider making
 *         the change in the kernel too (^T in kern/tty.c).
 *
 *      TODO - consider whether pctcpu should be used
 *
 */

#include <sys/param.h>
#include <sys/time.h>
#include <sys/proc.h>

#include "extern.h"

#define isrun(p)        (((p)->p_stat == SRUN) || ((p)->p_stat == SIDL))

#define TESTAB(a, b)    ((a)<<1 | (b))
#define ONLYA   2
#define ONLYB   1
#define BOTH    3

int
proc_compare(p1, p2)
        register struct proc *p1, *p2;
{

        if (p1 == NULL)
                return (1);
        /*
         * see if at least one of them is runnable
         */
        switch (TESTAB(isrun(p1), isrun(p2))) {
        case ONLYA:
                return (0);
        case ONLYB:
                return (1);
        case BOTH:
                /*
                 * tie - favor one with highest recent cpu utilization
                 */
                if (p2->p_cpu > p1->p_cpu)
                        return (1);
                if (p1->p_cpu > p2->p_cpu)
                        return (0);
                return (p2->p_pid > p1->p_pid); /* tie - return highest pid */
        }
        /*
         * weed out zombies
         */
        switch (TESTAB(p1->p_stat == SZOMB, p2->p_stat == SZOMB)) {
        case ONLYA:
                return (1);
        case ONLYB:
                return (0);
        case BOTH:
                return (p2->p_pid > p1->p_pid); /* tie - return highest pid */
        }
        /*
         * pick the one with the smallest sleep time
         */
        if (p2->p_slptime > p1->p_slptime)
                return (0);
        if (p1->p_slptime > p2->p_slptime)
                return (1);
        /*
         * favor one sleeping in a non-interruptible sleep
         */
         if (p1->p_flag&SSINTR && (p2->p_flag&SSINTR) == 0)
                 return (1);
         if (p2->p_flag&SSINTR && (p1->p_flag&SSINTR) == 0)
                 return (0);
        return(p2->p_pid > p1->p_pid);          /* tie - return highest pid */
}