1 /* $NetBSD: kern_synch.c,v 1.46 1997/10/10 08:19:44 mycroft Exp $ */ 2 3 /*- 4 * Copyright (c) 1982, 1986, 1990, 1991, 1993 5 * The Regents of the University of California. All rights reserved. 6 * (c) UNIX System Laboratories, Inc. 7 * All or some portions of this file are derived from material licensed 8 * to the University of California by American Telephone and Telegraph 9 * Co. or Unix System Laboratories, Inc. and are reproduced herein with 10 * the permission of UNIX System Laboratories, Inc. 11 * 12 * Redistribution and use in source and binary forms, with or without 13 * modification, are permitted provided that the following conditions 14 * are met: 15 * 1. Redistributions of source code must retain the above copyright 16 * notice, this list of conditions and the following disclaimer. 17 * 2. Redistributions in binary form must reproduce the above copyright 18 * notice, this list of conditions and the following disclaimer in the 19 * documentation and/or other materials provided with the distribution. 20 * 3. All advertising materials mentioning features or use of this software 21 * must display the following acknowledgement: 22 * This product includes software developed by the University of 23 * California, Berkeley and its contributors. 24 * 4. Neither the name of the University nor the names of its contributors 25 * may be used to endorse or promote products derived from this software 26 * without specific prior written permission. 27 * 28 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 29 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 30 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 31 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 32 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 33 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 34 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 35 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 37 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 38 * SUCH DAMAGE. 39 * 40 * @(#)kern_synch.c 8.6 (Berkeley) 1/21/94 41 */ 42 43 #include <sys/param.h> 44 #include <sys/systm.h> 45 #include <sys/proc.h> 46 #include <sys/kernel.h> 47 #include <sys/buf.h> 48 #include <sys/signalvar.h> 49 #include <sys/resourcevar.h> 50 #include <vm/vm.h> 51 #ifdef KTRACE 52 #include <sys/ktrace.h> 53 #endif 54 55 #include <machine/cpu.h> 56 57 u_char curpriority; /* usrpri of curproc */ 58 int lbolt; /* once a second sleep address */ 59 60 void roundrobin __P((void *)); 61 void schedcpu __P((void *)); 62 void updatepri __P((struct proc *)); 63 void endtsleep __P((void *)); 64 65 /* 66 * Force switch among equal priority processes every 100ms. 67 */ 68 /* ARGSUSED */ 69 void 70 roundrobin(arg) 71 void *arg; 72 { 73 74 need_resched(); 75 timeout(roundrobin, NULL, hz / 10); 76 } 77 78 /* 79 * Constants for digital decay and forget: 80 * 90% of (p_estcpu) usage in 5 * loadav time 81 * 95% of (p_pctcpu) usage in 60 seconds (load insensitive) 82 * Note that, as ps(1) mentions, this can let percentages 83 * total over 100% (I've seen 137.9% for 3 processes). 84 * 85 * Note that hardclock updates p_estcpu and p_cpticks independently. 86 * 87 * We wish to decay away 90% of p_estcpu in (5 * loadavg) seconds. 88 * That is, the system wants to compute a value of decay such 89 * that the following for loop: 90 * for (i = 0; i < (5 * loadavg); i++) 91 * p_estcpu *= decay; 92 * will compute 93 * p_estcpu *= 0.1; 94 * for all values of loadavg: 95 * 96 * Mathematically this loop can be expressed by saying: 97 * decay ** (5 * loadavg) ~= .1 98 * 99 * The system computes decay as: 100 * decay = (2 * loadavg) / (2 * loadavg + 1) 101 * 102 * We wish to prove that the system's computation of decay 103 * will always fulfill the equation: 104 * decay ** (5 * loadavg) ~= .1 105 * 106 * If we compute b as: 107 * b = 2 * loadavg 108 * then 109 * decay = b / (b + 1) 110 * 111 * We now need to prove two things: 112 * 1) Given factor ** (5 * loadavg) ~= .1, prove factor == b/(b+1) 113 * 2) Given b/(b+1) ** power ~= .1, prove power == (5 * loadavg) 114 * 115 * Facts: 116 * For x close to zero, exp(x) =~ 1 + x, since 117 * exp(x) = 0! + x**1/1! + x**2/2! + ... . 118 * therefore exp(-1/b) =~ 1 - (1/b) = (b-1)/b. 119 * For x close to zero, ln(1+x) =~ x, since 120 * ln(1+x) = x - x**2/2 + x**3/3 - ... -1 < x < 1 121 * therefore ln(b/(b+1)) = ln(1 - 1/(b+1)) =~ -1/(b+1). 122 * ln(.1) =~ -2.30 123 * 124 * Proof of (1): 125 * Solve (factor)**(power) =~ .1 given power (5*loadav): 126 * solving for factor, 127 * ln(factor) =~ (-2.30/5*loadav), or 128 * factor =~ exp(-1/((5/2.30)*loadav)) =~ exp(-1/(2*loadav)) = 129 * exp(-1/b) =~ (b-1)/b =~ b/(b+1). QED 130 * 131 * Proof of (2): 132 * Solve (factor)**(power) =~ .1 given factor == (b/(b+1)): 133 * solving for power, 134 * power*ln(b/(b+1)) =~ -2.30, or 135 * power =~ 2.3 * (b + 1) = 4.6*loadav + 2.3 =~ 5*loadav. QED 136 * 137 * Actual power values for the implemented algorithm are as follows: 138 * loadav: 1 2 3 4 139 * power: 5.68 10.32 14.94 19.55 140 */ 141 142 /* calculations for digital decay to forget 90% of usage in 5*loadav sec */ 143 #define loadfactor(loadav) (2 * (loadav)) 144 #define decay_cpu(loadfac, cpu) (((loadfac) * (cpu)) / ((loadfac) + FSCALE)) 145 146 /* decay 95% of `p_pctcpu' in 60 seconds; see CCPU_SHIFT before changing */ 147 fixpt_t ccpu = 0.95122942450071400909 * FSCALE; /* exp(-1/20) */ 148 149 /* 150 * If `ccpu' is not equal to `exp(-1/20)' and you still want to use the 151 * faster/more-accurate formula, you'll have to estimate CCPU_SHIFT below 152 * and possibly adjust FSHIFT in "param.h" so that (FSHIFT >= CCPU_SHIFT). 153 * 154 * To estimate CCPU_SHIFT for exp(-1/20), the following formula was used: 155 * 1 - exp(-1/20) ~= 0.0487 ~= 0.0488 == 1 (fixed pt, *11* bits). 156 * 157 * If you dont want to bother with the faster/more-accurate formula, you 158 * can set CCPU_SHIFT to (FSHIFT + 1) which will use a slower/less-accurate 159 * (more general) method of calculating the %age of CPU used by a process. 160 */ 161 #define CCPU_SHIFT 11 162 163 /* 164 * Recompute process priorities, every hz ticks. 165 */ 166 /* ARGSUSED */ 167 void 168 schedcpu(arg) 169 void *arg; 170 { 171 register fixpt_t loadfac = loadfactor(averunnable.ldavg[0]); 172 register struct proc *p; 173 register int s; 174 register unsigned int newcpu; 175 176 wakeup((caddr_t)&lbolt); 177 for (p = allproc.lh_first; p != 0; p = p->p_list.le_next) { 178 /* 179 * Increment time in/out of memory and sleep time 180 * (if sleeping). We ignore overflow; with 16-bit int's 181 * (remember them?) overflow takes 45 days. 182 */ 183 p->p_swtime++; 184 if (p->p_stat == SSLEEP || p->p_stat == SSTOP) 185 p->p_slptime++; 186 p->p_pctcpu = (p->p_pctcpu * ccpu) >> FSHIFT; 187 /* 188 * If the process has slept the entire second, 189 * stop recalculating its priority until it wakes up. 190 */ 191 if (p->p_slptime > 1) 192 continue; 193 s = splstatclock(); /* prevent state changes */ 194 /* 195 * p_pctcpu is only for ps. 196 */ 197 #if (FSHIFT >= CCPU_SHIFT) 198 p->p_pctcpu += (hz == 100)? 199 ((fixpt_t) p->p_cpticks) << (FSHIFT - CCPU_SHIFT): 200 100 * (((fixpt_t) p->p_cpticks) 201 << (FSHIFT - CCPU_SHIFT)) / hz; 202 #else 203 p->p_pctcpu += ((FSCALE - ccpu) * 204 (p->p_cpticks * FSCALE / hz)) >> FSHIFT; 205 #endif 206 p->p_cpticks = 0; 207 newcpu = (u_int)decay_cpu(loadfac, p->p_estcpu) 208 + p->p_nice - NZERO; 209 p->p_estcpu = min(newcpu, UCHAR_MAX); 210 resetpriority(p); 211 if (p->p_priority >= PUSER) { 212 #define PPQ (128 / NQS) /* priorities per queue */ 213 if ((p != curproc) && 214 p->p_stat == SRUN && 215 (p->p_flag & P_INMEM) && 216 (p->p_priority / PPQ) != (p->p_usrpri / PPQ)) { 217 remrunqueue(p); 218 p->p_priority = p->p_usrpri; 219 setrunqueue(p); 220 } else 221 p->p_priority = p->p_usrpri; 222 } 223 splx(s); 224 } 225 vmmeter(); 226 timeout(schedcpu, (void *)0, hz); 227 } 228 229 /* 230 * Recalculate the priority of a process after it has slept for a while. 231 * For all load averages >= 1 and max p_estcpu of 255, sleeping for at 232 * least six times the loadfactor will decay p_estcpu to zero. 233 */ 234 void 235 updatepri(p) 236 register struct proc *p; 237 { 238 register unsigned int newcpu = p->p_estcpu; 239 register fixpt_t loadfac = loadfactor(averunnable.ldavg[0]); 240 241 if (p->p_slptime > 5 * loadfac) 242 p->p_estcpu = 0; 243 else { 244 p->p_slptime--; /* the first time was done in schedcpu */ 245 while (newcpu && --p->p_slptime) 246 newcpu = (int) decay_cpu(loadfac, newcpu); 247 p->p_estcpu = min(newcpu, UCHAR_MAX); 248 } 249 resetpriority(p); 250 } 251 252 /* 253 * We're only looking at 7 bits of the address; everything is 254 * aligned to 4, lots of things are aligned to greater powers 255 * of 2. Shift right by 8, i.e. drop the bottom 256 worth. 256 */ 257 #define TABLESIZE 128 258 #define LOOKUP(x) (((long)(x) >> 8) & (TABLESIZE - 1)) 259 struct slpque { 260 struct proc *sq_head; 261 struct proc **sq_tailp; 262 } slpque[TABLESIZE]; 263 264 /* 265 * During autoconfiguration or after a panic, a sleep will simply 266 * lower the priority briefly to allow interrupts, then return. 267 * The priority to be used (safepri) is machine-dependent, thus this 268 * value is initialized and maintained in the machine-dependent layers. 269 * This priority will typically be 0, or the lowest priority 270 * that is safe for use on the interrupt stack; it can be made 271 * higher to block network software interrupts after panics. 272 */ 273 int safepri; 274 275 /* 276 * General sleep call. Suspends the current process until a wakeup is 277 * performed on the specified identifier. The process will then be made 278 * runnable with the specified priority. Sleeps at most timo/hz seconds 279 * (0 means no timeout). If pri includes PCATCH flag, signals are checked 280 * before and after sleeping, else signals are not checked. Returns 0 if 281 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a 282 * signal needs to be delivered, ERESTART is returned if the current system 283 * call should be restarted if possible, and EINTR is returned if the system 284 * call should be interrupted by the signal (return EINTR). 285 */ 286 int 287 tsleep(ident, priority, wmesg, timo) 288 void *ident; 289 int priority, timo; 290 const char *wmesg; 291 { 292 register struct proc *p = curproc; 293 register struct slpque *qp; 294 register s; 295 int sig, catch = priority & PCATCH; 296 extern int cold; 297 void endtsleep __P((void *)); 298 299 if (cold || panicstr) { 300 /* 301 * After a panic, or during autoconfiguration, 302 * just give interrupts a chance, then just return; 303 * don't run any other procs or panic below, 304 * in case this is the idle process and already asleep. 305 */ 306 s = splhigh(); 307 splx(safepri); 308 splx(s); 309 return (0); 310 } 311 312 #ifdef KTRACE 313 if (KTRPOINT(p, KTR_CSW)) 314 ktrcsw(p->p_tracep, 1, 0); 315 #endif 316 s = splhigh(); 317 318 #ifdef DIAGNOSTIC 319 if (ident == NULL || p->p_stat != SRUN || p->p_back) 320 panic("tsleep"); 321 #endif 322 p->p_wchan = ident; 323 p->p_wmesg = wmesg; 324 p->p_slptime = 0; 325 p->p_priority = priority & PRIMASK; 326 qp = &slpque[LOOKUP(ident)]; 327 if (qp->sq_head == 0) 328 qp->sq_head = p; 329 else 330 *qp->sq_tailp = p; 331 *(qp->sq_tailp = &p->p_forw) = 0; 332 if (timo) 333 timeout(endtsleep, (void *)p, timo); 334 /* 335 * We put ourselves on the sleep queue and start our timeout 336 * before calling CURSIG, as we could stop there, and a wakeup 337 * or a SIGCONT (or both) could occur while we were stopped. 338 * A SIGCONT would cause us to be marked as SSLEEP 339 * without resuming us, thus we must be ready for sleep 340 * when CURSIG is called. If the wakeup happens while we're 341 * stopped, p->p_wchan will be 0 upon return from CURSIG. 342 */ 343 if (catch) { 344 p->p_flag |= P_SINTR; 345 if ((sig = CURSIG(p)) != 0) { 346 if (p->p_wchan) 347 unsleep(p); 348 p->p_stat = SRUN; 349 goto resume; 350 } 351 if (p->p_wchan == 0) { 352 catch = 0; 353 goto resume; 354 } 355 } else 356 sig = 0; 357 p->p_stat = SSLEEP; 358 p->p_stats->p_ru.ru_nvcsw++; 359 mi_switch(); 360 #ifdef DDB 361 /* handy breakpoint location after process "wakes" */ 362 asm(".globl bpendtsleep ; bpendtsleep:"); 363 #endif 364 resume: 365 curpriority = p->p_usrpri; 366 splx(s); 367 p->p_flag &= ~P_SINTR; 368 if (p->p_flag & P_TIMEOUT) { 369 p->p_flag &= ~P_TIMEOUT; 370 if (sig == 0) { 371 #ifdef KTRACE 372 if (KTRPOINT(p, KTR_CSW)) 373 ktrcsw(p->p_tracep, 0, 0); 374 #endif 375 return (EWOULDBLOCK); 376 } 377 } else if (timo) 378 untimeout(endtsleep, (void *)p); 379 if (catch && (sig != 0 || (sig = CURSIG(p)) != 0)) { 380 #ifdef KTRACE 381 if (KTRPOINT(p, KTR_CSW)) 382 ktrcsw(p->p_tracep, 0, 0); 383 #endif 384 if (p->p_sigacts->ps_sigintr & sigmask(sig)) 385 return (EINTR); 386 return (ERESTART); 387 } 388 #ifdef KTRACE 389 if (KTRPOINT(p, KTR_CSW)) 390 ktrcsw(p->p_tracep, 0, 0); 391 #endif 392 return (0); 393 } 394 395 /* 396 * Implement timeout for tsleep. 397 * If process hasn't been awakened (wchan non-zero), 398 * set timeout flag and undo the sleep. If proc 399 * is stopped, just unsleep so it will remain stopped. 400 */ 401 void 402 endtsleep(arg) 403 void *arg; 404 { 405 register struct proc *p; 406 int s; 407 408 p = (struct proc *)arg; 409 s = splhigh(); 410 if (p->p_wchan) { 411 if (p->p_stat == SSLEEP) 412 setrunnable(p); 413 else 414 unsleep(p); 415 p->p_flag |= P_TIMEOUT; 416 } 417 splx(s); 418 } 419 420 /* 421 * Short-term, non-interruptable sleep. 422 */ 423 void 424 sleep(ident, priority) 425 void *ident; 426 int priority; 427 { 428 register struct proc *p = curproc; 429 register struct slpque *qp; 430 register s; 431 extern int cold; 432 433 #ifdef DIAGNOSTIC 434 if (priority > PZERO) { 435 printf("sleep called with priority %d > PZERO, wchan: %p\n", 436 priority, ident); 437 panic("old sleep"); 438 } 439 #endif 440 s = splhigh(); 441 if (cold || panicstr) { 442 /* 443 * After a panic, or during autoconfiguration, 444 * just give interrupts a chance, then just return; 445 * don't run any other procs or panic below, 446 * in case this is the idle process and already asleep. 447 */ 448 splx(safepri); 449 splx(s); 450 return; 451 } 452 #ifdef DIAGNOSTIC 453 if (ident == NULL || p->p_stat != SRUN || p->p_back) 454 panic("sleep"); 455 #endif 456 p->p_wchan = ident; 457 p->p_wmesg = NULL; 458 p->p_slptime = 0; 459 p->p_priority = priority; 460 qp = &slpque[LOOKUP(ident)]; 461 if (qp->sq_head == 0) 462 qp->sq_head = p; 463 else 464 *qp->sq_tailp = p; 465 *(qp->sq_tailp = &p->p_forw) = 0; 466 p->p_stat = SSLEEP; 467 p->p_stats->p_ru.ru_nvcsw++; 468 #ifdef KTRACE 469 if (KTRPOINT(p, KTR_CSW)) 470 ktrcsw(p->p_tracep, 1, 0); 471 #endif 472 mi_switch(); 473 #ifdef DDB 474 /* handy breakpoint location after process "wakes" */ 475 asm(".globl bpendsleep ; bpendsleep:"); 476 #endif 477 #ifdef KTRACE 478 if (KTRPOINT(p, KTR_CSW)) 479 ktrcsw(p->p_tracep, 0, 0); 480 #endif 481 curpriority = p->p_usrpri; 482 splx(s); 483 } 484 485 /* 486 * Remove a process from its wait queue 487 */ 488 void 489 unsleep(p) 490 register struct proc *p; 491 { 492 register struct slpque *qp; 493 register struct proc **hp; 494 int s; 495 496 s = splhigh(); 497 if (p->p_wchan) { 498 hp = &(qp = &slpque[LOOKUP(p->p_wchan)])->sq_head; 499 while (*hp != p) 500 hp = &(*hp)->p_forw; 501 *hp = p->p_forw; 502 if (qp->sq_tailp == &p->p_forw) 503 qp->sq_tailp = hp; 504 p->p_wchan = 0; 505 } 506 splx(s); 507 } 508 509 /* 510 * Make all processes sleeping on the specified identifier runnable. 511 */ 512 void 513 wakeup(ident) 514 register void *ident; 515 { 516 register struct slpque *qp; 517 register struct proc *p, **q; 518 int s; 519 520 s = splhigh(); 521 qp = &slpque[LOOKUP(ident)]; 522 restart: 523 for (q = &qp->sq_head; (p = *q) != NULL; ) { 524 #ifdef DIAGNOSTIC 525 if (p->p_back || (p->p_stat != SSLEEP && p->p_stat != SSTOP)) 526 panic("wakeup"); 527 #endif 528 if (p->p_wchan == ident) { 529 p->p_wchan = 0; 530 *q = p->p_forw; 531 if (qp->sq_tailp == &p->p_forw) 532 qp->sq_tailp = q; 533 if (p->p_stat == SSLEEP) { 534 /* OPTIMIZED EXPANSION OF setrunnable(p); */ 535 if (p->p_slptime > 1) 536 updatepri(p); 537 p->p_slptime = 0; 538 p->p_stat = SRUN; 539 if (p->p_flag & P_INMEM) 540 setrunqueue(p); 541 /* 542 * Since curpriority is a user priority, 543 * p->p_priority is always better than 544 * curpriority. 545 */ 546 if ((p->p_flag & P_INMEM) == 0) 547 wakeup((caddr_t)&proc0); 548 else 549 need_resched(); 550 /* END INLINE EXPANSION */ 551 goto restart; 552 } 553 } else 554 q = &p->p_forw; 555 } 556 splx(s); 557 } 558 559 /* 560 * The machine independent parts of mi_switch(). 561 * Must be called at splstatclock() or higher. 562 */ 563 void 564 mi_switch() 565 { 566 register struct proc *p = curproc; /* XXX */ 567 register struct rlimit *rlim; 568 register long s, u; 569 struct timeval tv; 570 571 /* 572 * Compute the amount of time during which the current 573 * process was running, and add that to its total so far. 574 */ 575 microtime(&tv); 576 u = p->p_rtime.tv_usec + (tv.tv_usec - runtime.tv_usec); 577 s = p->p_rtime.tv_sec + (tv.tv_sec - runtime.tv_sec); 578 if (u < 0) { 579 u += 1000000; 580 s--; 581 } else if (u >= 1000000) { 582 u -= 1000000; 583 s++; 584 } 585 p->p_rtime.tv_usec = u; 586 p->p_rtime.tv_sec = s; 587 588 /* 589 * Check if the process exceeds its cpu resource allocation. 590 * If over max, kill it. In any case, if it has run for more 591 * than 10 minutes, reduce priority to give others a chance. 592 */ 593 rlim = &p->p_rlimit[RLIMIT_CPU]; 594 if (s >= rlim->rlim_cur) { 595 if (s >= rlim->rlim_max) 596 psignal(p, SIGKILL); 597 else { 598 psignal(p, SIGXCPU); 599 if (rlim->rlim_cur < rlim->rlim_max) 600 rlim->rlim_cur += 5; 601 } 602 } 603 if (autonicetime && s > autonicetime && p->p_ucred->cr_uid && p->p_nice == NZERO) { 604 p->p_nice = autoniceval + NZERO; 605 resetpriority(p); 606 } 607 608 /* 609 * Pick a new current process and record its start time. 610 */ 611 cnt.v_swtch++; 612 cpu_switch(p); 613 microtime(&runtime); 614 } 615 616 /* 617 * Initialize the (doubly-linked) run queues 618 * to be empty. 619 */ 620 void 621 rqinit() 622 { 623 register int i; 624 625 for (i = 0; i < NQS; i++) 626 qs[i].ph_link = qs[i].ph_rlink = (struct proc *)&qs[i]; 627 } 628 629 /* 630 * Change process state to be runnable, 631 * placing it on the run queue if it is in memory, 632 * and awakening the swapper if it isn't in memory. 633 */ 634 void 635 setrunnable(p) 636 register struct proc *p; 637 { 638 register int s; 639 640 s = splhigh(); 641 switch (p->p_stat) { 642 case 0: 643 case SRUN: 644 case SZOMB: 645 default: 646 panic("setrunnable"); 647 case SSTOP: 648 /* 649 * If we're being traced (possibly because someone attached us 650 * while we were stopped), check for a signal from the debugger. 651 */ 652 if ((p->p_flag & P_TRACED) != 0 && p->p_xstat != 0) 653 p->p_siglist |= sigmask(p->p_xstat); 654 case SSLEEP: 655 unsleep(p); /* e.g. when sending signals */ 656 break; 657 658 case SIDL: 659 break; 660 } 661 p->p_stat = SRUN; 662 if (p->p_flag & P_INMEM) 663 setrunqueue(p); 664 splx(s); 665 if (p->p_slptime > 1) 666 updatepri(p); 667 p->p_slptime = 0; 668 if ((p->p_flag & P_INMEM) == 0) 669 wakeup((caddr_t)&proc0); 670 else if (p->p_priority < curpriority) 671 need_resched(); 672 } 673 674 /* 675 * Compute the priority of a process when running in user mode. 676 * Arrange to reschedule if the resulting priority is better 677 * than that of the current process. 678 */ 679 void 680 resetpriority(p) 681 register struct proc *p; 682 { 683 register unsigned int newpriority; 684 685 newpriority = PUSER + p->p_estcpu / 4 + 2 * (p->p_nice - NZERO); 686 newpriority = min(newpriority, MAXPRI); 687 p->p_usrpri = newpriority; 688 if (newpriority < curpriority) 689 need_resched(); 690 } 691