sched_4bsd.c revision 1.13.6.2
1 /* $NetBSD: sched_4bsd.c,v 1.13.6.2 2008/06/02 13:24:10 mjf Exp $ */ 2 3 /*- 4 * Copyright (c) 1999, 2000, 2004, 2006, 2007, 2008 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Jason R. Thorpe of the Numerical Aerospace Simulation Facility, 9 * NASA Ames Research Center, by Charles M. Hannum, Andrew Doran, and 10 * Daniel Sieger. 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 * 21 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 22 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 23 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 24 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 25 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 26 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 27 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 28 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 29 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 30 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 31 * POSSIBILITY OF SUCH DAMAGE. 32 */ 33 34 /*- 35 * Copyright (c) 1982, 1986, 1990, 1991, 1993 36 * The Regents of the University of California. All rights reserved. 37 * (c) UNIX System Laboratories, Inc. 38 * All or some portions of this file are derived from material licensed 39 * to the University of California by American Telephone and Telegraph 40 * Co. or Unix System Laboratories, Inc. and are reproduced herein with 41 * the permission of UNIX System Laboratories, Inc. 42 * 43 * Redistribution and use in source and binary forms, with or without 44 * modification, are permitted provided that the following conditions 45 * are met: 46 * 1. Redistributions of source code must retain the above copyright 47 * notice, this list of conditions and the following disclaimer. 48 * 2. Redistributions in binary form must reproduce the above copyright 49 * notice, this list of conditions and the following disclaimer in the 50 * documentation and/or other materials provided with the distribution. 51 * 3. Neither the name of the University nor the names of its contributors 52 * may be used to endorse or promote products derived from this software 53 * without specific prior written permission. 54 * 55 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 56 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 57 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 58 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 59 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 60 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 61 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 62 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 63 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 64 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 65 * SUCH DAMAGE. 66 * 67 * @(#)kern_synch.c 8.9 (Berkeley) 5/19/95 68 */ 69 70 #include <sys/cdefs.h> 71 __KERNEL_RCSID(0, "$NetBSD: sched_4bsd.c,v 1.13.6.2 2008/06/02 13:24:10 mjf Exp $"); 72 73 #include "opt_ddb.h" 74 #include "opt_lockdebug.h" 75 #include "opt_perfctrs.h" 76 77 #include <sys/param.h> 78 #include <sys/systm.h> 79 #include <sys/callout.h> 80 #include <sys/cpu.h> 81 #include <sys/proc.h> 82 #include <sys/kernel.h> 83 #include <sys/signalvar.h> 84 #include <sys/resourcevar.h> 85 #include <sys/sched.h> 86 #include <sys/sysctl.h> 87 #include <sys/kauth.h> 88 #include <sys/lockdebug.h> 89 #include <sys/kmem.h> 90 #include <sys/intr.h> 91 92 #include <uvm/uvm_extern.h> 93 94 static void updatepri(struct lwp *); 95 static void resetpriority(struct lwp *); 96 97 extern unsigned int sched_pstats_ticks; /* defined in kern_synch.c */ 98 99 /* Number of hardclock ticks per sched_tick() */ 100 static int rrticks; 101 102 /* 103 * Force switch among equal priority processes every 100ms. 104 * Called from hardclock every hz/10 == rrticks hardclock ticks. 105 * 106 * There's no need to lock anywhere in this routine, as it's 107 * CPU-local and runs at IPL_SCHED (called from clock interrupt). 108 */ 109 /* ARGSUSED */ 110 void 111 sched_tick(struct cpu_info *ci) 112 { 113 struct schedstate_percpu *spc = &ci->ci_schedstate; 114 lwp_t *l; 115 116 spc->spc_ticks = rrticks; 117 118 if (CURCPU_IDLE_P()) { 119 cpu_need_resched(ci, 0); 120 return; 121 } 122 l = ci->ci_data.cpu_onproc; 123 if (l == NULL) { 124 return; 125 } 126 switch (l->l_class) { 127 case SCHED_FIFO: 128 /* No timeslicing for FIFO jobs. */ 129 break; 130 case SCHED_RR: 131 /* Force it into mi_switch() to look for other jobs to run. */ 132 cpu_need_resched(ci, RESCHED_KPREEMPT); 133 break; 134 default: 135 if (spc->spc_flags & SPCF_SHOULDYIELD) { 136 /* 137 * Process is stuck in kernel somewhere, probably 138 * due to buggy or inefficient code. Force a 139 * kernel preemption. 140 */ 141 cpu_need_resched(ci, RESCHED_KPREEMPT); 142 } else if (spc->spc_flags & SPCF_SEENRR) { 143 /* 144 * The process has already been through a roundrobin 145 * without switching and may be hogging the CPU. 146 * Indicate that the process should yield. 147 */ 148 spc->spc_flags |= SPCF_SHOULDYIELD; 149 cpu_need_resched(ci, 0); 150 } else { 151 spc->spc_flags |= SPCF_SEENRR; 152 } 153 break; 154 } 155 } 156 157 /* 158 * Why PRIO_MAX - 2? From setpriority(2): 159 * 160 * prio is a value in the range -20 to 20. The default priority is 161 * 0; lower priorities cause more favorable scheduling. A value of 162 * 19 or 20 will schedule a process only when nothing at priority <= 163 * 0 is runnable. 164 * 165 * This gives estcpu influence over 18 priority levels, and leaves nice 166 * with 40 levels. One way to think about it is that nice has 20 levels 167 * either side of estcpu's 18. 168 */ 169 #define ESTCPU_SHIFT 11 170 #define ESTCPU_MAX ((PRIO_MAX - 2) << ESTCPU_SHIFT) 171 #define ESTCPU_ACCUM (1 << (ESTCPU_SHIFT - 1)) 172 #define ESTCPULIM(e) min((e), ESTCPU_MAX) 173 174 /* 175 * Constants for digital decay and forget: 176 * 90% of (l_estcpu) usage in 5 * loadav time 177 * 95% of (l_pctcpu) usage in 60 seconds (load insensitive) 178 * Note that, as ps(1) mentions, this can let percentages 179 * total over 100% (I've seen 137.9% for 3 processes). 180 * 181 * Note that hardclock updates l_estcpu and l_cpticks independently. 182 * 183 * We wish to decay away 90% of l_estcpu in (5 * loadavg) seconds. 184 * That is, the system wants to compute a value of decay such 185 * that the following for loop: 186 * for (i = 0; i < (5 * loadavg); i++) 187 * l_estcpu *= decay; 188 * will compute 189 * l_estcpu *= 0.1; 190 * for all values of loadavg: 191 * 192 * Mathematically this loop can be expressed by saying: 193 * decay ** (5 * loadavg) ~= .1 194 * 195 * The system computes decay as: 196 * decay = (2 * loadavg) / (2 * loadavg + 1) 197 * 198 * We wish to prove that the system's computation of decay 199 * will always fulfill the equation: 200 * decay ** (5 * loadavg) ~= .1 201 * 202 * If we compute b as: 203 * b = 2 * loadavg 204 * then 205 * decay = b / (b + 1) 206 * 207 * We now need to prove two things: 208 * 1) Given factor ** (5 * loadavg) ~= .1, prove factor == b/(b+1) 209 * 2) Given b/(b+1) ** power ~= .1, prove power == (5 * loadavg) 210 * 211 * Facts: 212 * For x close to zero, exp(x) =~ 1 + x, since 213 * exp(x) = 0! + x**1/1! + x**2/2! + ... . 214 * therefore exp(-1/b) =~ 1 - (1/b) = (b-1)/b. 215 * For x close to zero, ln(1+x) =~ x, since 216 * ln(1+x) = x - x**2/2 + x**3/3 - ... -1 < x < 1 217 * therefore ln(b/(b+1)) = ln(1 - 1/(b+1)) =~ -1/(b+1). 218 * ln(.1) =~ -2.30 219 * 220 * Proof of (1): 221 * Solve (factor)**(power) =~ .1 given power (5*loadav): 222 * solving for factor, 223 * ln(factor) =~ (-2.30/5*loadav), or 224 * factor =~ exp(-1/((5/2.30)*loadav)) =~ exp(-1/(2*loadav)) = 225 * exp(-1/b) =~ (b-1)/b =~ b/(b+1). QED 226 * 227 * Proof of (2): 228 * Solve (factor)**(power) =~ .1 given factor == (b/(b+1)): 229 * solving for power, 230 * power*ln(b/(b+1)) =~ -2.30, or 231 * power =~ 2.3 * (b + 1) = 4.6*loadav + 2.3 =~ 5*loadav. QED 232 * 233 * Actual power values for the implemented algorithm are as follows: 234 * loadav: 1 2 3 4 235 * power: 5.68 10.32 14.94 19.55 236 */ 237 238 /* calculations for digital decay to forget 90% of usage in 5*loadav sec */ 239 #define loadfactor(loadav) (2 * (loadav)) 240 241 static fixpt_t 242 decay_cpu(fixpt_t loadfac, fixpt_t estcpu) 243 { 244 245 if (estcpu == 0) { 246 return 0; 247 } 248 249 #if !defined(_LP64) 250 /* avoid 64bit arithmetics. */ 251 #define FIXPT_MAX ((fixpt_t)((UINTMAX_C(1) << sizeof(fixpt_t) * CHAR_BIT) - 1)) 252 if (__predict_true(loadfac <= FIXPT_MAX / ESTCPU_MAX)) { 253 return estcpu * loadfac / (loadfac + FSCALE); 254 } 255 #endif /* !defined(_LP64) */ 256 257 return (uint64_t)estcpu * loadfac / (loadfac + FSCALE); 258 } 259 260 /* 261 * For all load averages >= 1 and max l_estcpu of (255 << ESTCPU_SHIFT), 262 * sleeping for at least seven times the loadfactor will decay l_estcpu to 263 * less than (1 << ESTCPU_SHIFT). 264 * 265 * note that our ESTCPU_MAX is actually much smaller than (255 << ESTCPU_SHIFT). 266 */ 267 static fixpt_t 268 decay_cpu_batch(fixpt_t loadfac, fixpt_t estcpu, unsigned int n) 269 { 270 271 if ((n << FSHIFT) >= 7 * loadfac) { 272 return 0; 273 } 274 275 while (estcpu != 0 && n > 1) { 276 estcpu = decay_cpu(loadfac, estcpu); 277 n--; 278 } 279 280 return estcpu; 281 } 282 283 /* 284 * sched_pstats_hook: 285 * 286 * Periodically called from sched_pstats(); used to recalculate priorities. 287 */ 288 void 289 sched_pstats_hook(struct lwp *l, int batch) 290 { 291 fixpt_t loadfac; 292 int sleeptm; 293 294 /* 295 * If the LWP has slept an entire second, stop recalculating 296 * its priority until it wakes up. 297 */ 298 if (l->l_stat == LSSLEEP || l->l_stat == LSSTOP || 299 l->l_stat == LSSUSPENDED) { 300 l->l_slptime++; 301 sleeptm = 1; 302 } else { 303 sleeptm = 0x7fffffff; 304 } 305 306 if (l->l_slptime <= sleeptm) { 307 loadfac = 2 * (averunnable.ldavg[0]); 308 l->l_estcpu = decay_cpu(loadfac, l->l_estcpu); 309 resetpriority(l); 310 } 311 } 312 313 /* 314 * Recalculate the priority of a process after it has slept for a while. 315 */ 316 static void 317 updatepri(struct lwp *l) 318 { 319 fixpt_t loadfac; 320 321 KASSERT(lwp_locked(l, NULL)); 322 KASSERT(l->l_slptime > 1); 323 324 loadfac = loadfactor(averunnable.ldavg[0]); 325 326 l->l_slptime--; /* the first time was done in sched_pstats */ 327 l->l_estcpu = decay_cpu_batch(loadfac, l->l_estcpu, l->l_slptime); 328 resetpriority(l); 329 } 330 331 void 332 sched_rqinit(void) 333 { 334 335 } 336 337 void 338 sched_setrunnable(struct lwp *l) 339 { 340 341 if (l->l_slptime > 1) 342 updatepri(l); 343 } 344 345 void 346 sched_nice(struct proc *p, int n) 347 { 348 struct lwp *l; 349 350 KASSERT(mutex_owned(p->p_lock)); 351 352 p->p_nice = n; 353 LIST_FOREACH(l, &p->p_lwps, l_sibling) { 354 lwp_lock(l); 355 resetpriority(l); 356 lwp_unlock(l); 357 } 358 } 359 360 /* 361 * Recompute the priority of an LWP. Arrange to reschedule if 362 * the resulting priority is better than that of the current LWP. 363 */ 364 static void 365 resetpriority(struct lwp *l) 366 { 367 pri_t pri; 368 struct proc *p = l->l_proc; 369 370 KASSERT(lwp_locked(l, NULL)); 371 372 if (l->l_class != SCHED_OTHER) 373 return; 374 375 /* See comments above ESTCPU_SHIFT definition. */ 376 pri = (PRI_KERNEL - 1) - (l->l_estcpu >> ESTCPU_SHIFT) - p->p_nice; 377 pri = imax(pri, 0); 378 if (pri != l->l_priority) 379 lwp_changepri(l, pri); 380 } 381 382 /* 383 * We adjust the priority of the current process. The priority of a process 384 * gets worse as it accumulates CPU time. The CPU usage estimator (l_estcpu) 385 * is increased here. The formula for computing priorities (in kern_synch.c) 386 * will compute a different value each time l_estcpu increases. This can 387 * cause a switch, but unless the priority crosses a PPQ boundary the actual 388 * queue will not change. The CPU usage estimator ramps up quite quickly 389 * when the process is running (linearly), and decays away exponentially, at 390 * a rate which is proportionally slower when the system is busy. The basic 391 * principle is that the system will 90% forget that the process used a lot 392 * of CPU time in 5 * loadav seconds. This causes the system to favor 393 * processes which haven't run much recently, and to round-robin among other 394 * processes. 395 */ 396 397 void 398 sched_schedclock(struct lwp *l) 399 { 400 401 if (l->l_class != SCHED_OTHER) 402 return; 403 404 KASSERT(!CURCPU_IDLE_P()); 405 l->l_estcpu = ESTCPULIM(l->l_estcpu + ESTCPU_ACCUM); 406 lwp_lock(l); 407 resetpriority(l); 408 lwp_unlock(l); 409 } 410 411 /* 412 * sched_proc_fork: 413 * 414 * Inherit the parent's scheduler history. 415 */ 416 void 417 sched_proc_fork(struct proc *parent, struct proc *child) 418 { 419 lwp_t *pl; 420 421 KASSERT(mutex_owned(parent->p_lock)); 422 423 pl = LIST_FIRST(&parent->p_lwps); 424 child->p_estcpu_inherited = pl->l_estcpu; 425 child->p_forktime = sched_pstats_ticks; 426 } 427 428 /* 429 * sched_proc_exit: 430 * 431 * Chargeback parents for the sins of their children. 432 */ 433 void 434 sched_proc_exit(struct proc *parent, struct proc *child) 435 { 436 fixpt_t loadfac = loadfactor(averunnable.ldavg[0]); 437 fixpt_t estcpu; 438 lwp_t *pl, *cl; 439 440 /* XXX Only if parent != init?? */ 441 442 mutex_enter(parent->p_lock); 443 pl = LIST_FIRST(&parent->p_lwps); 444 cl = LIST_FIRST(&child->p_lwps); 445 estcpu = decay_cpu_batch(loadfac, child->p_estcpu_inherited, 446 sched_pstats_ticks - child->p_forktime); 447 if (cl->l_estcpu > estcpu) { 448 lwp_lock(pl); 449 pl->l_estcpu = ESTCPULIM(pl->l_estcpu + cl->l_estcpu - estcpu); 450 lwp_unlock(pl); 451 } 452 mutex_exit(parent->p_lock); 453 } 454 455 void 456 sched_wakeup(struct lwp *l) 457 { 458 459 } 460 461 void 462 sched_slept(struct lwp *l) 463 { 464 465 } 466 467 void 468 sched_lwp_fork(struct lwp *l1, struct lwp *l2) 469 { 470 471 l2->l_estcpu = l1->l_estcpu; 472 } 473 474 void 475 sched_lwp_exit(struct lwp *l) 476 { 477 478 } 479 480 void 481 sched_lwp_collect(struct lwp *t) 482 { 483 lwp_t *l; 484 485 /* Absorb estcpu value of collected LWP. */ 486 l = curlwp; 487 lwp_lock(l); 488 l->l_estcpu += t->l_estcpu; 489 lwp_unlock(l); 490 } 491 492 void 493 sched_oncpu(lwp_t *l) 494 { 495 496 } 497 498 void 499 sched_newts(lwp_t *l) 500 { 501 502 } 503 504 /* 505 * Sysctl nodes and initialization. 506 */ 507 508 static int 509 sysctl_sched_rtts(SYSCTLFN_ARGS) 510 { 511 struct sysctlnode node; 512 int rttsms = hztoms(rrticks); 513 514 node = *rnode; 515 node.sysctl_data = &rttsms; 516 return sysctl_lookup(SYSCTLFN_CALL(&node)); 517 } 518 519 SYSCTL_SETUP(sysctl_sched_4bsd_setup, "sysctl sched setup") 520 { 521 const struct sysctlnode *node = NULL; 522 523 sysctl_createv(clog, 0, NULL, NULL, 524 CTLFLAG_PERMANENT, 525 CTLTYPE_NODE, "kern", NULL, 526 NULL, 0, NULL, 0, 527 CTL_KERN, CTL_EOL); 528 sysctl_createv(clog, 0, NULL, &node, 529 CTLFLAG_PERMANENT, 530 CTLTYPE_NODE, "sched", 531 SYSCTL_DESCR("Scheduler options"), 532 NULL, 0, NULL, 0, 533 CTL_KERN, CTL_CREATE, CTL_EOL); 534 535 if (node == NULL) 536 return; 537 538 rrticks = hz / 10; 539 540 sysctl_createv(NULL, 0, &node, NULL, 541 CTLFLAG_PERMANENT, 542 CTLTYPE_STRING, "name", NULL, 543 NULL, 0, __UNCONST("4.4BSD"), 0, 544 CTL_CREATE, CTL_EOL); 545 sysctl_createv(NULL, 0, &node, NULL, 546 CTLFLAG_PERMANENT, 547 CTLTYPE_INT, "rtts", 548 SYSCTL_DESCR("Round-robin time quantum (in miliseconds)"), 549 sysctl_sched_rtts, 0, NULL, 0, 550 CTL_CREATE, CTL_EOL); 551 } 552
Indexes created Tue Sep 30 06:09:59 GMT 2025