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 7.16 (Berkeley) 05/06/91 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 u_char curpri; /* usrpri of curproc */ 20 21 /* 22 * Force switch among equal priority processes every 100ms. 23 */ 24 roundrobin() 25 { 26 27 need_resched(); 28 timeout(roundrobin, (caddr_t)0, hz / 10); 29 } 30 31 /* 32 * constants for digital decay and forget 33 * 90% of (p_cpu) usage in 5*loadav time 34 * 95% of (p_pctcpu) usage in 60 seconds (load insensitive) 35 * Note that, as ps(1) mentions, this can let percentages 36 * total over 100% (I've seen 137.9% for 3 processes). 37 * 38 * Note that hardclock updates p_cpu and p_cpticks independently. 39 * 40 * We wish to decay away 90% of p_cpu in (5 * loadavg) seconds. 41 * That is, the system wants to compute a value of decay such 42 * that the following for loop: 43 * for (i = 0; i < (5 * loadavg); i++) 44 * p_cpu *= decay; 45 * will compute 46 * p_cpu *= 0.1; 47 * for all values of loadavg: 48 * 49 * Mathematically this loop can be expressed by saying: 50 * decay ** (5 * loadavg) ~= .1 51 * 52 * The system computes decay as: 53 * decay = (2 * loadavg) / (2 * loadavg + 1) 54 * 55 * We wish to prove that the system's computation of decay 56 * will always fulfill the equation: 57 * decay ** (5 * loadavg) ~= .1 58 * 59 * If we compute b as: 60 * b = 2 * loadavg 61 * then 62 * decay = b / (b + 1) 63 * 64 * We now need to prove two things: 65 * 1) Given factor ** (5 * loadavg) ~= .1, prove factor == b/(b+1) 66 * 2) Given b/(b+1) ** power ~= .1, prove power == (5 * loadavg) 67 * 68 * Facts: 69 * For x close to zero, exp(x) =~ 1 + x, since 70 * exp(x) = 0! + x**1/1! + x**2/2! + ... . 71 * therefore exp(-1/b) =~ 1 - (1/b) = (b-1)/b. 72 * For x close to zero, ln(1+x) =~ x, since 73 * ln(1+x) = x - x**2/2 + x**3/3 - ... -1 < x < 1 74 * therefore ln(b/(b+1)) = ln(1 - 1/(b+1)) =~ -1/(b+1). 75 * ln(.1) =~ -2.30 76 * 77 * Proof of (1): 78 * Solve (factor)**(power) =~ .1 given power (5*loadav): 79 * solving for factor, 80 * ln(factor) =~ (-2.30/5*loadav), or 81 * factor =~ exp(-1/((5/2.30)*loadav)) =~ exp(-1/(2*loadav)) = 82 * exp(-1/b) =~ (b-1)/b =~ b/(b+1). QED 83 * 84 * Proof of (2): 85 * Solve (factor)**(power) =~ .1 given factor == (b/(b+1)): 86 * solving for power, 87 * power*ln(b/(b+1)) =~ -2.30, or 88 * power =~ 2.3 * (b + 1) = 4.6*loadav + 2.3 =~ 5*loadav. QED 89 * 90 * Actual power values for the implemented algorithm are as follows: 91 * loadav: 1 2 3 4 92 * power: 5.68 10.32 14.94 19.55 93 */ 94 95 /* calculations for digital decay to forget 90% of usage in 5*loadav sec */ 96 #define loadfactor(loadav) (2 * (loadav)) 97 #define decay_cpu(loadfac, cpu) (((loadfac) * (cpu)) / ((loadfac) + FSCALE)) 98 99 /* decay 95% of `p_pctcpu' in 60 seconds; see CCPU_SHIFT before changing */ 100 fixpt_t ccpu = 0.95122942450071400909 * FSCALE; /* exp(-1/20) */ 101 102 /* 103 * If `ccpu' is not equal to `exp(-1/20)' and you still want to use the 104 * faster/more-accurate formula, you'll have to estimate CCPU_SHIFT below 105 * and possibly adjust FSHIFT in "param.h" so that (FSHIFT >= CCPU_SHIFT). 106 * 107 * To estimate CCPU_SHIFT for exp(-1/20), the following formula was used: 108 * 1 - exp(-1/20) ~= 0.0487 ~= 0.0488 == 1 (fixed pt, *11* bits). 109 * 110 * If you dont want to bother with the faster/more-accurate formula, you 111 * can set CCPU_SHIFT to (FSHIFT + 1) which will use a slower/less-accurate 112 * (more general) method of calculating the %age of CPU used by a process. 113 */ 114 #define CCPU_SHIFT 11 115 116 /* 117 * Recompute process priorities, once a second 118 */ 119 schedcpu() 120 { 121 register fixpt_t loadfac = loadfactor(averunnable[0]); 122 register struct proc *p; 123 register int s; 124 register unsigned int newcpu; 125 126 wakeup((caddr_t)&lbolt); 127 for (p = allproc; p != NULL; p = p->p_nxt) { 128 /* 129 * Increment time in/out of memory and sleep time 130 * (if sleeping). We ignore overflow; with 16-bit int's 131 * (remember them?) overflow takes 45 days. 132 */ 133 p->p_time++; 134 if (p->p_stat == SSLEEP || p->p_stat == SSTOP) 135 p->p_slptime++; 136 p->p_pctcpu = (p->p_pctcpu * ccpu) >> FSHIFT; 137 /* 138 * If the process has slept the entire second, 139 * stop recalculating its priority until it wakes up. 140 */ 141 if (p->p_slptime > 1) 142 continue; 143 /* 144 * p_pctcpu is only for ps. 145 */ 146 #if (FSHIFT >= CCPU_SHIFT) 147 p->p_pctcpu += (hz == 100)? 148 ((fixpt_t) p->p_cpticks) << (FSHIFT - CCPU_SHIFT): 149 100 * (((fixpt_t) p->p_cpticks) 150 << (FSHIFT - CCPU_SHIFT)) / hz; 151 #else 152 p->p_pctcpu += ((FSCALE - ccpu) * 153 (p->p_cpticks * FSCALE / hz)) >> FSHIFT; 154 #endif 155 p->p_cpticks = 0; 156 newcpu = (u_int) decay_cpu(loadfac, p->p_cpu) + p->p_nice; 157 p->p_cpu = min(newcpu, UCHAR_MAX); 158 setpri(p); 159 s = splhigh(); /* prevent state changes */ 160 if (p->p_pri >= PUSER) { 161 #define PPQ (128 / NQS) /* priorities per queue */ 162 if ((p != curproc) && 163 p->p_stat == SRUN && 164 (p->p_flag & SLOAD) && 165 (p->p_pri / PPQ) != (p->p_usrpri / PPQ)) { 166 remrq(p); 167 p->p_pri = p->p_usrpri; 168 setrq(p); 169 } else 170 p->p_pri = p->p_usrpri; 171 } 172 splx(s); 173 } 174 vmmeter(); 175 if (bclnlist != NULL) 176 wakeup((caddr_t)pageproc); 177 timeout(schedcpu, (caddr_t)0, hz); 178 } 179 180 /* 181 * Recalculate the priority of a process after it has slept for a while. 182 * For all load averages >= 1 and max p_cpu of 255, sleeping for at least 183 * six times the loadfactor will decay p_cpu to zero. 184 */ 185 updatepri(p) 186 register struct proc *p; 187 { 188 register unsigned int newcpu = p->p_cpu; 189 register fixpt_t loadfac = loadfactor(averunnable[0]); 190 191 if (p->p_slptime > 5 * loadfac) 192 p->p_cpu = 0; 193 else { 194 p->p_slptime--; /* the first time was done in schedcpu */ 195 while (newcpu && --p->p_slptime) 196 newcpu = (int) decay_cpu(loadfac, newcpu); 197 p->p_cpu = min(newcpu, UCHAR_MAX); 198 } 199 setpri(p); 200 } 201 202 #define SQSIZE 0100 /* Must be power of 2 */ 203 #define HASH(x) (( (int) x >> 5) & (SQSIZE-1)) 204 struct slpque { 205 struct proc *sq_head; 206 struct proc **sq_tailp; 207 } slpque[SQSIZE]; 208 209 /* 210 * During autoconfiguration or after a panic, a sleep will simply 211 * lower the priority briefly to allow interrupts, then return. 212 * The priority to be used (safepri) is machine-dependent, thus this 213 * value is initialized and maintained in the machine-dependent layers. 214 * This priority will typically be 0, or the lowest priority 215 * that is safe for use on the interrupt stack; it can be made 216 * higher to block network software interrupts after panics. 217 */ 218 int safepri; 219 220 /* 221 * General sleep call. 222 * Suspends current process until a wakeup is made on chan. 223 * The process will then be made runnable with priority pri. 224 * Sleeps at most timo/hz seconds (0 means no timeout). 225 * If pri includes PCATCH flag, signals are checked 226 * before and after sleeping, else signals are not checked. 227 * Returns 0 if awakened, EWOULDBLOCK if the timeout expires. 228 * If PCATCH is set and a signal needs to be delivered, 229 * ERESTART is returned if the current system call should be restarted 230 * if possible, and EINTR is returned if the system call should 231 * be interrupted by the signal (return EINTR). 232 */ 233 tsleep(chan, pri, wmesg, timo) 234 caddr_t chan; 235 int pri; 236 char *wmesg; 237 int timo; 238 { 239 register struct proc *p = curproc; 240 register struct slpque *qp; 241 register s; 242 int sig, catch = pri & PCATCH; 243 extern int cold; 244 int endtsleep(); 245 246 s = splhigh(); 247 if (cold || panicstr) { 248 /* 249 * After a panic, or during autoconfiguration, 250 * just give interrupts a chance, then just return; 251 * don't run any other procs or panic below, 252 * in case this is the idle process and already asleep. 253 */ 254 splx(safepri); 255 splx(s); 256 return (0); 257 } 258 #ifdef DIAGNOSTIC 259 if (chan == 0 || p->p_stat != SRUN || p->p_rlink) 260 panic("tsleep"); 261 #endif 262 p->p_wchan = chan; 263 p->p_wmesg = wmesg; 264 p->p_slptime = 0; 265 p->p_pri = pri & PRIMASK; 266 qp = &slpque[HASH(chan)]; 267 if (qp->sq_head == 0) 268 qp->sq_head = p; 269 else 270 *qp->sq_tailp = p; 271 *(qp->sq_tailp = &p->p_link) = 0; 272 if (timo) 273 timeout(endtsleep, (caddr_t)p, timo); 274 /* 275 * We put ourselves on the sleep queue and start our timeout 276 * before calling CURSIG, as we could stop there, and a wakeup 277 * or a SIGCONT (or both) could occur while we were stopped. 278 * A SIGCONT would cause us to be marked as SSLEEP 279 * without resuming us, thus we must be ready for sleep 280 * when CURSIG is called. If the wakeup happens while we're 281 * stopped, p->p_wchan will be 0 upon return from CURSIG. 282 */ 283 if (catch) { 284 p->p_flag |= SSINTR; 285 if (sig = CURSIG(p)) { 286 if (p->p_wchan) 287 unsleep(p); 288 p->p_stat = SRUN; 289 goto resume; 290 } 291 if (p->p_wchan == 0) { 292 catch = 0; 293 goto resume; 294 } 295 } 296 p->p_stat = SSLEEP; 297 (void) spl0(); 298 p->p_stats->p_ru.ru_nvcsw++; 299 swtch(); 300 resume: 301 curpri = p->p_usrpri; 302 splx(s); 303 p->p_flag &= ~SSINTR; 304 if (p->p_flag & STIMO) { 305 p->p_flag &= ~STIMO; 306 if (catch == 0 || sig == 0) 307 return (EWOULDBLOCK); 308 } else if (timo) 309 untimeout(endtsleep, (caddr_t)p); 310 if (catch && (sig != 0 || (sig = CURSIG(p)))) { 311 if (p->p_sigacts->ps_sigintr & sigmask(sig)) 312 return (EINTR); 313 return (ERESTART); 314 } 315 return (0); 316 } 317 318 /* 319 * Implement timeout for tsleep. 320 * If process hasn't been awakened (wchan non-zero), 321 * set timeout flag and undo the sleep. If proc 322 * is stopped, just unsleep so it will remain stopped. 323 */ 324 endtsleep(p) 325 register struct proc *p; 326 { 327 int s = splhigh(); 328 329 if (p->p_wchan) { 330 if (p->p_stat == SSLEEP) 331 setrun(p); 332 else 333 unsleep(p); 334 p->p_flag |= STIMO; 335 } 336 splx(s); 337 } 338 339 /* 340 * Short-term, non-interruptable sleep. 341 */ 342 sleep(chan, pri) 343 caddr_t chan; 344 int pri; 345 { 346 register struct proc *p = curproc; 347 register struct slpque *qp; 348 register s; 349 extern int cold; 350 351 #ifdef DIAGNOSTIC 352 if (pri > PZERO) { 353 printf("sleep called with pri %d > PZERO, wchan: %x\n", 354 pri, chan); 355 panic("old sleep"); 356 } 357 #endif 358 s = splhigh(); 359 if (cold || panicstr) { 360 /* 361 * After a panic, or during autoconfiguration, 362 * just give interrupts a chance, then just return; 363 * don't run any other procs or panic below, 364 * in case this is the idle process and already asleep. 365 */ 366 splx(safepri); 367 splx(s); 368 return; 369 } 370 #ifdef DIAGNOSTIC 371 if (chan==0 || p->p_stat != SRUN || p->p_rlink) 372 panic("sleep"); 373 #endif 374 p->p_wchan = chan; 375 p->p_wmesg = NULL; 376 p->p_slptime = 0; 377 p->p_pri = pri; 378 qp = &slpque[HASH(chan)]; 379 if (qp->sq_head == 0) 380 qp->sq_head = p; 381 else 382 *qp->sq_tailp = p; 383 *(qp->sq_tailp = &p->p_link) = 0; 384 p->p_stat = SSLEEP; 385 (void) spl0(); 386 p->p_stats->p_ru.ru_nvcsw++; 387 swtch(); 388 curpri = p->p_usrpri; 389 splx(s); 390 } 391 392 /* 393 * Remove a process from its wait queue 394 */ 395 unsleep(p) 396 register struct proc *p; 397 { 398 register struct slpque *qp; 399 register struct proc **hp; 400 int s; 401 402 s = splhigh(); 403 if (p->p_wchan) { 404 hp = &(qp = &slpque[HASH(p->p_wchan)])->sq_head; 405 while (*hp != p) 406 hp = &(*hp)->p_link; 407 *hp = p->p_link; 408 if (qp->sq_tailp == &p->p_link) 409 qp->sq_tailp = hp; 410 p->p_wchan = 0; 411 } 412 splx(s); 413 } 414 415 /* 416 * Wakeup on "chan"; set all processes 417 * sleeping on chan to run state. 418 */ 419 wakeup(chan) 420 register caddr_t chan; 421 { 422 register struct slpque *qp; 423 register struct proc *p, **q; 424 int s; 425 426 s = splhigh(); 427 qp = &slpque[HASH(chan)]; 428 restart: 429 for (q = &qp->sq_head; p = *q; ) { 430 #ifdef DIAGNOSTIC 431 if (p->p_rlink || p->p_stat != SSLEEP && p->p_stat != SSTOP) 432 panic("wakeup"); 433 #endif 434 if (p->p_wchan == chan) { 435 p->p_wchan = 0; 436 *q = p->p_link; 437 if (qp->sq_tailp == &p->p_link) 438 qp->sq_tailp = q; 439 if (p->p_stat == SSLEEP) { 440 /* OPTIMIZED INLINE EXPANSION OF setrun(p) */ 441 if (p->p_slptime > 1) 442 updatepri(p); 443 p->p_slptime = 0; 444 p->p_stat = SRUN; 445 if (p->p_flag & SLOAD) 446 setrq(p); 447 /* 448 * Since curpri is a usrpri, 449 * p->p_pri is always better than curpri. 450 */ 451 if ((p->p_flag&SLOAD) == 0) 452 wakeup((caddr_t)&proc0); 453 else 454 need_resched(); 455 /* END INLINE EXPANSION */ 456 goto restart; 457 } 458 } else 459 q = &p->p_link; 460 } 461 splx(s); 462 } 463 464 /* 465 * Initialize the (doubly-linked) run queues 466 * to be empty. 467 */ 468 rqinit() 469 { 470 register int i; 471 472 for (i = 0; i < NQS; i++) 473 qs[i].ph_link = qs[i].ph_rlink = (struct proc *)&qs[i]; 474 } 475 476 /* 477 * Change process state to be runnable, 478 * placing it on the run queue if it is in memory, 479 * and awakening the swapper if it isn't in memory. 480 */ 481 setrun(p) 482 register struct proc *p; 483 { 484 register int s; 485 486 s = splhigh(); 487 switch (p->p_stat) { 488 489 case 0: 490 case SWAIT: 491 case SRUN: 492 case SZOMB: 493 default: 494 panic("setrun"); 495 496 case SSTOP: 497 case SSLEEP: 498 unsleep(p); /* e.g. when sending signals */ 499 break; 500 501 case SIDL: 502 break; 503 } 504 p->p_stat = SRUN; 505 if (p->p_flag & SLOAD) 506 setrq(p); 507 splx(s); 508 if (p->p_slptime > 1) 509 updatepri(p); 510 p->p_slptime = 0; 511 if ((p->p_flag&SLOAD) == 0) 512 wakeup((caddr_t)&proc0); 513 else if (p->p_pri < curpri) 514 need_resched(); 515 } 516 517 /* 518 * Compute priority of process when running in user mode. 519 * Arrange to reschedule if the resulting priority 520 * is better than that of the current process. 521 */ 522 setpri(p) 523 register struct proc *p; 524 { 525 register unsigned int newpri; 526 527 newpri = PUSER + p->p_cpu / 4 + 2 * p->p_nice; 528 newpri = min(newpri, MAXPRI); 529 p->p_usrpri = newpri; 530 if (newpri < curpri) 531 need_resched(); 532 } 533