1 /* 2 * Copyright (c) 1982, 1986, 1990, 1991 Regents of the University of California. 3 * All rights reserved. The Berkeley software License Agreement 4 * specifies the terms and conditions for redistribution. 5 * 6 * @(#)kern_synch.c 7.15 (Berkeley) 05/04/91 7 */ 8 9 #include "param.h" 10 #include "systm.h" 11 #include "proc.h" 12 #include "kernel.h" 13 #include "buf.h" 14 #include "signalvar.h" 15 #include "resourcevar.h" 16 17 #include "machine/cpu.h" 18 19 /* 20 * Force switch among equal priority processes every 100ms. 21 */ 22 roundrobin() 23 { 24 25 need_resched(); 26 timeout(roundrobin, (caddr_t)0, hz / 10); 27 } 28 29 /* 30 * constants for digital decay and forget 31 * 90% of (p_cpu) usage in 5*loadav time 32 * 95% of (p_pctcpu) usage in 60 seconds (load insensitive) 33 * Note that, as ps(1) mentions, this can let percentages 34 * total over 100% (I've seen 137.9% for 3 processes). 35 * 36 * Note that hardclock updates p_cpu and p_cpticks independently. 37 * 38 * We wish to decay away 90% of p_cpu in (5 * loadavg) seconds. 39 * That is, the system wants to compute a value of decay such 40 * that the following for loop: 41 * for (i = 0; i < (5 * loadavg); i++) 42 * p_cpu *= decay; 43 * will compute 44 * p_cpu *= 0.1; 45 * for all values of loadavg: 46 * 47 * Mathematically this loop can be expressed by saying: 48 * decay ** (5 * loadavg) ~= .1 49 * 50 * The system computes decay as: 51 * decay = (2 * loadavg) / (2 * loadavg + 1) 52 * 53 * We wish to prove that the system's computation of decay 54 * will always fulfill the equation: 55 * decay ** (5 * loadavg) ~= .1 56 * 57 * If we compute b as: 58 * b = 2 * loadavg 59 * then 60 * decay = b / (b + 1) 61 * 62 * We now need to prove two things: 63 * 1) Given factor ** (5 * loadavg) ~= .1, prove factor == b/(b+1) 64 * 2) Given b/(b+1) ** power ~= .1, prove power == (5 * loadavg) 65 * 66 * Facts: 67 * For x close to zero, exp(x) =~ 1 + x, since 68 * exp(x) = 0! + x**1/1! + x**2/2! + ... . 69 * therefore exp(-1/b) =~ 1 - (1/b) = (b-1)/b. 70 * For x close to zero, ln(1+x) =~ x, since 71 * ln(1+x) = x - x**2/2 + x**3/3 - ... -1 < x < 1 72 * therefore ln(b/(b+1)) = ln(1 - 1/(b+1)) =~ -1/(b+1). 73 * ln(.1) =~ -2.30 74 * 75 * Proof of (1): 76 * Solve (factor)**(power) =~ .1 given power (5*loadav): 77 * solving for factor, 78 * ln(factor) =~ (-2.30/5*loadav), or 79 * factor =~ exp(-1/((5/2.30)*loadav)) =~ exp(-1/(2*loadav)) = 80 * exp(-1/b) =~ (b-1)/b =~ b/(b+1). QED 81 * 82 * Proof of (2): 83 * Solve (factor)**(power) =~ .1 given factor == (b/(b+1)): 84 * solving for power, 85 * power*ln(b/(b+1)) =~ -2.30, or 86 * power =~ 2.3 * (b + 1) = 4.6*loadav + 2.3 =~ 5*loadav. QED 87 * 88 * Actual power values for the implemented algorithm are as follows: 89 * loadav: 1 2 3 4 90 * power: 5.68 10.32 14.94 19.55 91 */ 92 93 /* calculations for digital decay to forget 90% of usage in 5*loadav sec */ 94 #define loadfactor(loadav) (2 * (loadav)) 95 #define decay_cpu(loadfac, cpu) (((loadfac) * (cpu)) / ((loadfac) + FSCALE)) 96 97 /* decay 95% of `p_pctcpu' in 60 seconds; see CCPU_SHIFT before changing */ 98 fixpt_t ccpu = 0.95122942450071400909 * FSCALE; /* exp(-1/20) */ 99 100 /* 101 * If `ccpu' is not equal to `exp(-1/20)' and you still want to use the 102 * faster/more-accurate formula, you'll have to estimate CCPU_SHIFT below 103 * and possibly adjust FSHIFT in "param.h" so that (FSHIFT >= CCPU_SHIFT). 104 * 105 * To estimate CCPU_SHIFT for exp(-1/20), the following formula was used: 106 * 1 - exp(-1/20) ~= 0.0487 ~= 0.0488 == 1 (fixed pt, *11* bits). 107 * 108 * If you dont want to bother with the faster/more-accurate formula, you 109 * can set CCPU_SHIFT to (FSHIFT + 1) which will use a slower/less-accurate 110 * (more general) method of calculating the %age of CPU used by a process. 111 */ 112 #define CCPU_SHIFT 11 113 114 /* 115 * Recompute process priorities, once a second 116 */ 117 schedcpu() 118 { 119 register fixpt_t loadfac = loadfactor(averunnable[0]); 120 register struct proc *p; 121 register int s; 122 register unsigned int newcpu; 123 124 wakeup((caddr_t)&lbolt); 125 for (p = allproc; p != NULL; p = p->p_nxt) { 126 /* 127 * Increment time in/out of memory and sleep time 128 * (if sleeping). We ignore overflow; with 16-bit int's 129 * (remember them?) overflow takes 45 days. 130 */ 131 p->p_time++; 132 if (p->p_stat == SSLEEP || p->p_stat == SSTOP) 133 p->p_slptime++; 134 p->p_pctcpu = (p->p_pctcpu * ccpu) >> FSHIFT; 135 /* 136 * If the process has slept the entire second, 137 * stop recalculating its priority until it wakes up. 138 */ 139 if (p->p_slptime > 1) 140 continue; 141 /* 142 * p_pctcpu is only for ps. 143 */ 144 #if (FSHIFT >= CCPU_SHIFT) 145 p->p_pctcpu += (hz == 100)? 146 ((fixpt_t) p->p_cpticks) << (FSHIFT - CCPU_SHIFT): 147 100 * (((fixpt_t) p->p_cpticks) 148 << (FSHIFT - CCPU_SHIFT)) / hz; 149 #else 150 p->p_pctcpu += ((FSCALE - ccpu) * 151 (p->p_cpticks * FSCALE / hz)) >> FSHIFT; 152 #endif 153 p->p_cpticks = 0; 154 newcpu = (u_int) decay_cpu(loadfac, p->p_cpu) + p->p_nice; 155 p->p_cpu = min(newcpu, UCHAR_MAX); 156 setpri(p); 157 s = splhigh(); /* prevent state changes */ 158 if (p->p_pri >= PUSER) { 159 #define PPQ (128 / NQS) /* priorities per queue */ 160 if ((p != curproc) && 161 p->p_stat == SRUN && 162 (p->p_flag & SLOAD) && 163 (p->p_pri / PPQ) != (p->p_usrpri / PPQ)) { 164 remrq(p); 165 p->p_pri = p->p_usrpri; 166 setrq(p); 167 } else 168 p->p_pri = p->p_usrpri; 169 } 170 splx(s); 171 } 172 vmmeter(); 173 if (bclnlist != NULL) 174 wakeup((caddr_t)pageproc); 175 timeout(schedcpu, (caddr_t)0, hz); 176 } 177 178 /* 179 * Recalculate the priority of a process after it has slept for a while. 180 * For all load averages >= 1 and max p_cpu of 255, sleeping for at least 181 * six times the loadfactor will decay p_cpu to zero. 182 */ 183 updatepri(p) 184 register struct proc *p; 185 { 186 register unsigned int newcpu = p->p_cpu; 187 register fixpt_t loadfac = loadfactor(averunnable[0]); 188 189 if (p->p_slptime > 5 * loadfac) 190 p->p_cpu = 0; 191 else { 192 p->p_slptime--; /* the first time was done in schedcpu */ 193 while (newcpu && --p->p_slptime) 194 newcpu = (int) decay_cpu(loadfac, newcpu); 195 p->p_cpu = min(newcpu, UCHAR_MAX); 196 } 197 setpri(p); 198 } 199 200 #define SQSIZE 0100 /* Must be power of 2 */ 201 #define HASH(x) (( (int) x >> 5) & (SQSIZE-1)) 202 struct slpque { 203 struct proc *sq_head; 204 struct proc **sq_tailp; 205 } slpque[SQSIZE]; 206 207 /* 208 * During autoconfiguration or after a panic, a sleep will simply 209 * lower the priority briefly to allow interrupts, then return. 210 * The priority to be used (safepri) is machine-dependent, thus this 211 * value is initialized and maintained in the machine-dependent layers. 212 * This priority will typically be 0, or the lowest priority 213 * that is safe for use on the interrupt stack; it can be made 214 * higher to block network software interrupts after panics. 215 */ 216 int safepri; 217 218 /* 219 * General sleep call. 220 * Suspends current process until a wakeup is made on chan. 221 * The process will then be made runnable with priority pri. 222 * Sleeps at most timo/hz seconds (0 means no timeout). 223 * If pri includes PCATCH flag, signals are checked 224 * before and after sleeping, else signals are not checked. 225 * Returns 0 if awakened, EWOULDBLOCK if the timeout expires. 226 * If PCATCH is set and a signal needs to be delivered, 227 * ERESTART is returned if the current system call should be restarted 228 * if possible, and EINTR is returned if the system call should 229 * be interrupted by the signal (return EINTR). 230 */ 231 tsleep(chan, pri, wmesg, timo) 232 caddr_t chan; 233 int pri; 234 char *wmesg; 235 int timo; 236 { 237 register struct proc *p = curproc; 238 register struct slpque *qp; 239 register s; 240 int sig, catch = pri & PCATCH; 241 extern int cold; 242 int endtsleep(); 243 244 s = splhigh(); 245 if (cold || panicstr) { 246 /* 247 * After a panic, or during autoconfiguration, 248 * just give interrupts a chance, then just return; 249 * don't run any other procs or panic below, 250 * in case this is the idle process and already asleep. 251 */ 252 splx(safepri); 253 splx(s); 254 return (0); 255 } 256 #ifdef DIAGNOSTIC 257 if (chan == 0 || p->p_stat != SRUN || p->p_rlink) 258 panic("tsleep"); 259 #endif 260 p->p_wchan = chan; 261 p->p_wmesg = wmesg; 262 p->p_slptime = 0; 263 p->p_pri = pri & PRIMASK; 264 qp = &slpque[HASH(chan)]; 265 if (qp->sq_head == 0) 266 qp->sq_head = p; 267 else 268 *qp->sq_tailp = p; 269 *(qp->sq_tailp = &p->p_link) = 0; 270 if (timo) 271 timeout(endtsleep, (caddr_t)p, timo); 272 /* 273 * We put ourselves on the sleep queue and start our timeout 274 * before calling CURSIG, as we could stop there, and a wakeup 275 * or a SIGCONT (or both) could occur while we were stopped. 276 * A SIGCONT would cause us to be marked as SSLEEP 277 * without resuming us, thus we must be ready for sleep 278 * when CURSIG is called. If the wakeup happens while we're 279 * stopped, p->p_wchan will be 0 upon return from CURSIG. 280 */ 281 if (catch) { 282 p->p_flag |= SSINTR; 283 if (sig = CURSIG(p)) { 284 if (p->p_wchan) 285 unsleep(p); 286 p->p_stat = SRUN; 287 goto resume; 288 } 289 if (p->p_wchan == 0) { 290 catch = 0; 291 goto resume; 292 } 293 } 294 p->p_stat = SSLEEP; 295 (void) spl0(); 296 p->p_stats->p_ru.ru_nvcsw++; 297 swtch(); 298 resume: 299 curpri = p->p_usrpri; 300 splx(s); 301 p->p_flag &= ~SSINTR; 302 if (p->p_flag & STIMO) { 303 p->p_flag &= ~STIMO; 304 if (catch == 0 || sig == 0) 305 return (EWOULDBLOCK); 306 } else if (timo) 307 untimeout(endtsleep, (caddr_t)p); 308 if (catch && (sig != 0 || (sig = CURSIG(p)))) { 309 if (p->p_sigacts->ps_sigintr & sigmask(sig)) 310 return (EINTR); 311 return (ERESTART); 312 } 313 return (0); 314 } 315 316 /* 317 * Implement timeout for tsleep. 318 * If process hasn't been awakened (wchan non-zero), 319 * set timeout flag and undo the sleep. If proc 320 * is stopped, just unsleep so it will remain stopped. 321 */ 322 endtsleep(p) 323 register struct proc *p; 324 { 325 int s = splhigh(); 326 327 if (p->p_wchan) { 328 if (p->p_stat == SSLEEP) 329 setrun(p); 330 else 331 unsleep(p); 332 p->p_flag |= STIMO; 333 } 334 splx(s); 335 } 336 337 /* 338 * Short-term, non-interruptable sleep. 339 */ 340 sleep(chan, pri) 341 caddr_t chan; 342 int pri; 343 { 344 register struct proc *p = curproc; 345 register struct slpque *qp; 346 register s; 347 extern int cold; 348 349 #ifdef DIAGNOSTIC 350 if (pri > PZERO) { 351 printf("sleep called with pri %d > PZERO, wchan: %x\n", 352 pri, chan); 353 panic("old sleep"); 354 } 355 #endif 356 s = splhigh(); 357 if (cold || panicstr) { 358 /* 359 * After a panic, or during autoconfiguration, 360 * just give interrupts a chance, then just return; 361 * don't run any other procs or panic below, 362 * in case this is the idle process and already asleep. 363 */ 364 splx(safepri); 365 splx(s); 366 return; 367 } 368 #ifdef DIAGNOSTIC 369 if (chan==0 || p->p_stat != SRUN || p->p_rlink) 370 panic("sleep"); 371 #endif 372 p->p_wchan = chan; 373 p->p_wmesg = NULL; 374 p->p_slptime = 0; 375 p->p_pri = pri; 376 qp = &slpque[HASH(chan)]; 377 if (qp->sq_head == 0) 378 qp->sq_head = p; 379 else 380 *qp->sq_tailp = p; 381 *(qp->sq_tailp = &p->p_link) = 0; 382 p->p_stat = SSLEEP; 383 (void) spl0(); 384 p->p_stats->p_ru.ru_nvcsw++; 385 swtch(); 386 curpri = p->p_usrpri; 387 splx(s); 388 } 389 390 /* 391 * Remove a process from its wait queue 392 */ 393 unsleep(p) 394 register struct proc *p; 395 { 396 register struct slpque *qp; 397 register struct proc **hp; 398 int s; 399 400 s = splhigh(); 401 if (p->p_wchan) { 402 hp = &(qp = &slpque[HASH(p->p_wchan)])->sq_head; 403 while (*hp != p) 404 hp = &(*hp)->p_link; 405 *hp = p->p_link; 406 if (qp->sq_tailp == &p->p_link) 407 qp->sq_tailp = hp; 408 p->p_wchan = 0; 409 } 410 splx(s); 411 } 412 413 /* 414 * Wakeup on "chan"; set all processes 415 * sleeping on chan to run state. 416 */ 417 wakeup(chan) 418 register caddr_t chan; 419 { 420 register struct slpque *qp; 421 register struct proc *p, **q; 422 int s; 423 424 s = splhigh(); 425 qp = &slpque[HASH(chan)]; 426 restart: 427 for (q = &qp->sq_head; p = *q; ) { 428 #ifdef DIAGNOSTIC 429 if (p->p_rlink || p->p_stat != SSLEEP && p->p_stat != SSTOP) 430 panic("wakeup"); 431 #endif 432 if (p->p_wchan == chan) { 433 p->p_wchan = 0; 434 *q = p->p_link; 435 if (qp->sq_tailp == &p->p_link) 436 qp->sq_tailp = q; 437 if (p->p_stat == SSLEEP) { 438 /* OPTIMIZED INLINE EXPANSION OF setrun(p) */ 439 if (p->p_slptime > 1) 440 updatepri(p); 441 p->p_slptime = 0; 442 p->p_stat = SRUN; 443 if (p->p_flag & SLOAD) 444 setrq(p); 445 /* 446 * Since curpri is a usrpri, 447 * p->p_pri is always better than curpri. 448 */ 449 if ((p->p_flag&SLOAD) == 0) 450 wakeup((caddr_t)&proc0); 451 else 452 need_resched(); 453 /* END INLINE EXPANSION */ 454 goto restart; 455 } 456 } else 457 q = &p->p_link; 458 } 459 splx(s); 460 } 461 462 /* 463 * Initialize the (doubly-linked) run queues 464 * to be empty. 465 */ 466 rqinit() 467 { 468 register int i; 469 470 for (i = 0; i < NQS; i++) 471 qs[i].ph_link = qs[i].ph_rlink = (struct proc *)&qs[i]; 472 } 473 474 /* 475 * Change process state to be runnable, 476 * placing it on the run queue if it is in memory, 477 * and awakening the swapper if it isn't in memory. 478 */ 479 setrun(p) 480 register struct proc *p; 481 { 482 register int s; 483 484 s = splhigh(); 485 switch (p->p_stat) { 486 487 case 0: 488 case SWAIT: 489 case SRUN: 490 case SZOMB: 491 default: 492 panic("setrun"); 493 494 case SSTOP: 495 case SSLEEP: 496 unsleep(p); /* e.g. when sending signals */ 497 break; 498 499 case SIDL: 500 break; 501 } 502 p->p_stat = SRUN; 503 if (p->p_flag & SLOAD) 504 setrq(p); 505 splx(s); 506 if (p->p_slptime > 1) 507 updatepri(p); 508 p->p_slptime = 0; 509 if ((p->p_flag&SLOAD) == 0) 510 wakeup((caddr_t)&proc0); 511 else if (p->p_pri < curpri) 512 need_resched(); 513 } 514 515 /* 516 * Compute priority of process when running in user mode. 517 * Arrange to reschedule if the resulting priority 518 * is better than that of the current process. 519 */ 520 setpri(p) 521 register struct proc *p; 522 { 523 register unsigned int newpri; 524 525 newpri = PUSER + p->p_cpu / 4 + 2 * p->p_nice; 526 newpri = min(newpri, MAXPRI); 527 p->p_usrpri = newpri; 528 if (newpri < curpri) 529 need_resched(); 530 } 531