FreeBSD/Linux Kernel Cross Reference
sys/kern/sched_4bsd.c
1 /* $NetBSD: sched_4bsd.c,v 1.24.4.1 2009/06/06 22:12:44 bouyer 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 1.24.4.1 2009/06/06 22:12:44 bouyer 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
293 /*
294 * If the LWP has slept an entire second, stop recalculating
295 * its priority until it wakes up.
296 */
297 KASSERT(lwp_locked(l, NULL));
298 if (l->l_stat == LSSLEEP || l->l_stat == LSSTOP ||
299 l->l_stat == LSSUSPENDED) {
300 if (l->l_slptime > 1) {
301 return;
302 }
303 }
304 loadfac = 2 * (averunnable.ldavg[0]);
305 l->l_estcpu = decay_cpu(loadfac, l->l_estcpu);
306 resetpriority(l);
307 }
308
309 /*
310 * Recalculate the priority of a process after it has slept for a while.
311 */
312 static void
313 updatepri(struct lwp *l)
314 {
315 fixpt_t loadfac;
316
317 KASSERT(lwp_locked(l, NULL));
318 KASSERT(l->l_slptime > 1);
319
320 loadfac = loadfactor(averunnable.ldavg[0]);
321
322 l->l_slptime--; /* the first time was done in sched_pstats */
323 l->l_estcpu = decay_cpu_batch(loadfac, l->l_estcpu, l->l_slptime);
324 resetpriority(l);
325 }
326
327 void
328 sched_rqinit(void)
329 {
330
331 }
332
333 void
334 sched_setrunnable(struct lwp *l)
335 {
336
337 if (l->l_slptime > 1)
338 updatepri(l);
339 }
340
341 void
342 sched_nice(struct proc *p, int n)
343 {
344 struct lwp *l;
345
346 KASSERT(mutex_owned(p->p_lock));
347
348 p->p_nice = n;
349 LIST_FOREACH(l, &p->p_lwps, l_sibling) {
350 lwp_lock(l);
351 resetpriority(l);
352 lwp_unlock(l);
353 }
354 }
355
356 /*
357 * Recompute the priority of an LWP. Arrange to reschedule if
358 * the resulting priority is better than that of the current LWP.
359 */
360 static void
361 resetpriority(struct lwp *l)
362 {
363 pri_t pri;
364 struct proc *p = l->l_proc;
365
366 KASSERT(lwp_locked(l, NULL));
367
368 if (l->l_class != SCHED_OTHER)
369 return;
370
371 /* See comments above ESTCPU_SHIFT definition. */
372 pri = (PRI_KERNEL - 1) - (l->l_estcpu >> ESTCPU_SHIFT) - p->p_nice;
373 pri = imax(pri, 0);
374 if (pri != l->l_priority)
375 lwp_changepri(l, pri);
376 }
377
378 /*
379 * We adjust the priority of the current process. The priority of a process
380 * gets worse as it accumulates CPU time. The CPU usage estimator (l_estcpu)
381 * is increased here. The formula for computing priorities (in kern_synch.c)
382 * will compute a different value each time l_estcpu increases. This can
383 * cause a switch, but unless the priority crosses a PPQ boundary the actual
384 * queue will not change. The CPU usage estimator ramps up quite quickly
385 * when the process is running (linearly), and decays away exponentially, at
386 * a rate which is proportionally slower when the system is busy. The basic
387 * principle is that the system will 90% forget that the process used a lot
388 * of CPU time in 5 * loadav seconds. This causes the system to favor
389 * processes which haven't run much recently, and to round-robin among other
390 * processes.
391 */
392
393 void
394 sched_schedclock(struct lwp *l)
395 {
396
397 if (l->l_class != SCHED_OTHER)
398 return;
399
400 KASSERT(!CURCPU_IDLE_P());
401 l->l_estcpu = ESTCPULIM(l->l_estcpu + ESTCPU_ACCUM);
402 lwp_lock(l);
403 resetpriority(l);
404 lwp_unlock(l);
405 }
406
407 /*
408 * sched_proc_fork:
409 *
410 * Inherit the parent's scheduler history.
411 */
412 void
413 sched_proc_fork(struct proc *parent, struct proc *child)
414 {
415 lwp_t *pl;
416
417 KASSERT(mutex_owned(parent->p_lock));
418
419 pl = LIST_FIRST(&parent->p_lwps);
420 child->p_estcpu_inherited = pl->l_estcpu;
421 child->p_forktime = sched_pstats_ticks;
422 }
423
424 /*
425 * sched_proc_exit:
426 *
427 * Chargeback parents for the sins of their children.
428 */
429 void
430 sched_proc_exit(struct proc *parent, struct proc *child)
431 {
432 fixpt_t loadfac = loadfactor(averunnable.ldavg[0]);
433 fixpt_t estcpu;
434 lwp_t *pl, *cl;
435
436 /* XXX Only if parent != init?? */
437
438 mutex_enter(parent->p_lock);
439 pl = LIST_FIRST(&parent->p_lwps);
440 cl = LIST_FIRST(&child->p_lwps);
441 estcpu = decay_cpu_batch(loadfac, child->p_estcpu_inherited,
442 sched_pstats_ticks - child->p_forktime);
443 if (cl->l_estcpu > estcpu) {
444 lwp_lock(pl);
445 pl->l_estcpu = ESTCPULIM(pl->l_estcpu + cl->l_estcpu - estcpu);
446 lwp_unlock(pl);
447 }
448 mutex_exit(parent->p_lock);
449 }
450
451 void
452 sched_wakeup(struct lwp *l)
453 {
454
455 }
456
457 void
458 sched_slept(struct lwp *l)
459 {
460
461 }
462
463 void
464 sched_lwp_fork(struct lwp *l1, struct lwp *l2)
465 {
466
467 l2->l_estcpu = l1->l_estcpu;
468 }
469
470 void
471 sched_lwp_collect(struct lwp *t)
472 {
473 lwp_t *l;
474
475 /* Absorb estcpu value of collected LWP. */
476 l = curlwp;
477 lwp_lock(l);
478 l->l_estcpu += t->l_estcpu;
479 lwp_unlock(l);
480 }
481
482 void
483 sched_oncpu(lwp_t *l)
484 {
485
486 }
487
488 void
489 sched_newts(lwp_t *l)
490 {
491
492 }
493
494 /*
495 * Sysctl nodes and initialization.
496 */
497
498 static int
499 sysctl_sched_rtts(SYSCTLFN_ARGS)
500 {
501 struct sysctlnode node;
502 int rttsms = hztoms(rrticks);
503
504 node = *rnode;
505 node.sysctl_data = &rttsms;
506 return sysctl_lookup(SYSCTLFN_CALL(&node));
507 }
508
509 SYSCTL_SETUP(sysctl_sched_4bsd_setup, "sysctl sched setup")
510 {
511 const struct sysctlnode *node = NULL;
512
513 sysctl_createv(clog, 0, NULL, NULL,
514 CTLFLAG_PERMANENT,
515 CTLTYPE_NODE, "kern", NULL,
516 NULL, 0, NULL, 0,
517 CTL_KERN, CTL_EOL);
518 sysctl_createv(clog, 0, NULL, &node,
519 CTLFLAG_PERMANENT,
520 CTLTYPE_NODE, "sched",
521 SYSCTL_DESCR("Scheduler options"),
522 NULL, 0, NULL, 0,
523 CTL_KERN, CTL_CREATE, CTL_EOL);
524
525 if (node == NULL)
526 return;
527
528 rrticks = hz / 10;
529
530 sysctl_createv(NULL, 0, &node, NULL,
531 CTLFLAG_PERMANENT,
532 CTLTYPE_STRING, "name", NULL,
533 NULL, 0, __UNCONST("4.4BSD"), 0,
534 CTL_CREATE, CTL_EOL);
535 sysctl_createv(NULL, 0, &node, NULL,
536 CTLFLAG_PERMANENT,
537 CTLTYPE_INT, "rtts",
538 SYSCTL_DESCR("Round-robin time quantum (in miliseconds)"),
539 sysctl_sched_rtts, 0, NULL, 0,
540 CTL_CREATE, CTL_EOL);
541 }
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