1 /*- 2 * Copyright (c) 1990 The Regents of the University of California. 3 * All rights reserved. 4 * 5 * %sccs.include.redist.c% 6 */ 7 8 #ifndef lint 9 static char sccsid[] = "@(#)proc_compare.c 5.4 (Berkeley) 02/07/91"; 10 #endif /* not lint */ 11 12 /* 13 * Returns 1 if p2 is more active than p1 14 * 15 * The algorithm for picking the "more active" process is thus: 16 * 17 * 1) Runnable processes are favored over anything 18 * else. The runner with the highest cpu 19 * utilization is picked (p_cpu). Ties are 20 * broken by picking the highest pid. 21 * 2) Next, the sleeper with the shortest sleep 22 * time is favored. With ties, we pick out 23 * just short-term sleepers (p_pri <= PZERO). 24 * Further ties are broken by picking the highest 25 * pid. 26 * 27 * NOTE - if you change this, be sure to consider making 28 * the change in the kernel too (^T in kern/tty.c). 29 * 30 * TODO - consider whether pctcpu should be used 31 * 32 */ 33 34 #include <sys/param.h> 35 #include <sys/time.h> 36 #include <sys/proc.h> 37 38 #define isrun(p) (((p)->p_stat == SRUN) || ((p)->p_stat == SIDL)) 39 40 #define TESTAB(a, b) ((a)<<1 | (b)) 41 #define ONLYA 2 42 #define ONLYB 1 43 #define BOTH 3 44 45 proc_compare(p1, p2) 46 register struct proc *p1, *p2; 47 { 48 49 if (p1 == NULL) 50 return (1); 51 /* 52 * see if at least one of them is runnable 53 */ 54 switch (TESTAB(isrun(p1), isrun(p2))) { 55 case ONLYA: 56 return (0); 57 case ONLYB: 58 return (1); 59 case BOTH: 60 /* 61 * tie - favor one with highest recent cpu utilization 62 */ 63 if (p2->p_cpu > p1->p_cpu) 64 return (1); 65 if (p1->p_cpu > p2->p_cpu) 66 return (0); 67 return (p2->p_pid > p1->p_pid); /* tie - return highest pid */ 68 } 69 /* 70 * weed out zombies 71 */ 72 switch (TESTAB(p1->p_stat == SZOMB, p2->p_stat == SZOMB)) { 73 case ONLYA: 74 return (1); 75 case ONLYB: 76 return (0); 77 case BOTH: 78 return (p2->p_pid > p1->p_pid); /* tie - return highest pid */ 79 } 80 /* 81 * pick the one with the smallest sleep time 82 */ 83 if (p2->p_slptime > p1->p_slptime) 84 return (0); 85 if (p1->p_slptime > p2->p_slptime) 86 return (1); 87 /* 88 * favor one sleeping in a non-interruptible sleep 89 */ 90 if (p1->p_flag&SSINTR && (p2->p_flag&SSINTR) == 0) 91 return (1); 92 if (p2->p_flag&SSINTR && (p1->p_flag&SSINTR) == 0) 93 return (0); 94 return(p2->p_pid > p1->p_pid); /* tie - return highest pid */ 95 } 96