sys/kern/usched_dummy.c

   1 /*
   2  * Copyright (c) 2006 The DragonFly Project.  All rights reserved.
   3  *
   4  * This code is derived from software contributed to The DragonFly Project
   5  * by Matthew Dillon <dillon@backplane.com>
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  *
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in
  15  *    the documentation and/or other materials provided with the
  16  *    distribution.
  17  * 3. Neither the name of The DragonFly Project nor the names of its
  18  *    contributors may be used to endorse or promote products derived
  19  *    from this software without specific, prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  22  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  23  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  24  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  25  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  26  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
  27  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  28  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  29  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  30  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  31  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  *
  34  * $DragonFly: src/sys/kern/usched_dummy.c,v 1.9 2008/04/21 15:24:46 dillon Exp $
  35  */
  36
  37 #include <sys/param.h>
  38 #include <sys/systm.h>
  39 #include <sys/kernel.h>
  40 #include <sys/lock.h>
  41 #include <sys/queue.h>
  42 #include <sys/proc.h>
  43 #include <sys/rtprio.h>
  44 #include <sys/uio.h>
  45 #include <sys/sysctl.h>
  46 #include <sys/resourcevar.h>
  47 #include <sys/spinlock.h>
  48 #include <machine/cpu.h>
  49 #include <machine/smp.h>
  50
  51 #include <sys/thread2.h>
  52 #include <sys/spinlock2.h>
  53 #include <sys/mplock2.h>
  54
  55 #define MAXPRI                  128
  56 #define PRIBASE_REALTIME        0
  57 #define PRIBASE_NORMAL          MAXPRI
  58 #define PRIBASE_IDLE            (MAXPRI * 2)
  59 #define PRIBASE_THREAD          (MAXPRI * 3)
  60 #define PRIBASE_NULL            (MAXPRI * 4)
  61
  62 #define lwp_priority    lwp_usdata.bsd4.priority
  63 #define lwp_estcpu      lwp_usdata.bsd4.estcpu
  64
  65 static void dummy_acquire_curproc(struct lwp *lp);
  66 static void dummy_release_curproc(struct lwp *lp);
  67 static void dummy_select_curproc(globaldata_t gd);
  68 static void dummy_setrunqueue(struct lwp *lp);
  69 static void dummy_schedulerclock(struct lwp *lp, sysclock_t period,
  70                                 sysclock_t cpstamp);
  71 static void dummy_recalculate_estcpu(struct lwp *lp);
  72 static void dummy_resetpriority(struct lwp *lp);
  73 static void dummy_forking(struct lwp *plp, struct lwp *lp);
  74 static void dummy_exiting(struct lwp *plp, struct lwp *lp);
  75 static void dummy_yield(struct lwp *lp);
  76
  77 struct usched usched_dummy = {
  78         { NULL },
  79         "dummy", "Dummy DragonFly Scheduler",
  80         NULL,                   /* default registration */
  81         NULL,                   /* default deregistration */
  82         dummy_acquire_curproc,
  83         dummy_release_curproc,
  84         dummy_setrunqueue,
  85         dummy_schedulerclock,
  86         dummy_recalculate_estcpu,
  87         dummy_resetpriority,
  88         dummy_forking,
  89         dummy_exiting,
  90         NULL,                   /* setcpumask not supported */
  91         dummy_yield
  92 };
  93
  94 struct usched_dummy_pcpu {
  95         int     rrcount;
  96         struct thread helper_thread;
  97         struct lwp *uschedcp;
  98 };
  99
 100 typedef struct usched_dummy_pcpu *dummy_pcpu_t;
 101
 102 static struct usched_dummy_pcpu dummy_pcpu[MAXCPU];
 103 static cpumask_t dummy_curprocmask = -1;
 104 static cpumask_t dummy_rdyprocmask;
 105 static struct spinlock dummy_spin;
 106 static TAILQ_HEAD(rq, lwp) dummy_runq;
 107 static int dummy_runqcount;
 108
 109 static int usched_dummy_rrinterval = (ESTCPUFREQ + 9) / 10;
 110 SYSCTL_INT(_kern, OID_AUTO, usched_dummy_rrinterval, CTLFLAG_RW,
 111         &usched_dummy_rrinterval, 0, "");
 112
 113 /*
 114  * Initialize the run queues at boot time, clear cpu 0 in curprocmask
 115  * to allow dummy scheduling on cpu 0.
 116  */
 117 static void
 118 dummyinit(void *dummy)
 119 {
 120         TAILQ_INIT(&dummy_runq);
 121         spin_init(&dummy_spin);
 122         atomic_clear_int(&dummy_curprocmask, 1);
 123 }
 124 SYSINIT(runqueue, SI_BOOT2_USCHED, SI_ORDER_FIRST, dummyinit, NULL)
 125
 126 /*
 127  * DUMMY_ACQUIRE_CURPROC
 128  *
 129  * This function is called when the kernel intends to return to userland.
 130  * It is responsible for making the thread the current designated userland
 131  * thread for this cpu, blocking if necessary.
 132  *
 133  * We are expected to handle userland reschedule requests here too.
 134  *
 135  * WARNING! THIS FUNCTION IS ALLOWED TO CAUSE THE CURRENT THREAD TO MIGRATE
 136  * TO ANOTHER CPU!  Because most of the kernel assumes that no migration will
 137  * occur, this function is called only under very controlled circumstances.
 138  *
 139  * MPSAFE
 140  */
 141 static void
 142 dummy_acquire_curproc(struct lwp *lp)
 143 {
 144         globaldata_t gd = mycpu;
 145         dummy_pcpu_t dd = &dummy_pcpu[gd->gd_cpuid];
 146         thread_t td = lp->lwp_thread;
 147
 148         /*
 149          * Possibly select another thread
 150          */
 151         if (user_resched_wanted())
 152                 dummy_select_curproc(gd);
 153
 154         /*
 155          * If this cpu has no current thread, select ourself
 156          */
 157         if (dd->uschedcp == lp ||
 158             (dd->uschedcp == NULL && TAILQ_EMPTY(&dummy_runq))) {
 159                 atomic_set_int(&dummy_curprocmask, gd->gd_cpumask);
 160                 dd->uschedcp = lp;
 161                 return;
 162         }
 163
 164         /*
 165          * If this cpu's current user process thread is not our thread,
 166          * deschedule ourselves and place us on the run queue, then
 167          * switch away.
 168          *
 169          * We loop until we become the current process.  Its a good idea
 170          * to run any passive release(s) before we mess with the scheduler
 171          * so our thread is in the expected state.
 172          */
 173         KKASSERT(dd->uschedcp != lp);
 174         if (td->td_release)
 175                 td->td_release(lp->lwp_thread);
 176         do {
 177                 crit_enter();
 178                 lwkt_deschedule_self(td);
 179                 dummy_setrunqueue(lp);
 180                 if ((td->td_flags & TDF_RUNQ) == 0)
 181                         ++lp->lwp_ru.ru_nivcsw;
 182                 lwkt_switch();          /* WE MAY MIGRATE TO ANOTHER CPU */
 183                 crit_exit();
 184                 gd = mycpu;
 185                 dd = &dummy_pcpu[gd->gd_cpuid];
 186                 KKASSERT((lp->lwp_flag & LWP_ONRUNQ) == 0);
 187         } while (dd->uschedcp != lp);
 188 }
 189
 190 /*
 191  * DUMMY_RELEASE_CURPROC
 192  *
 193  * This routine detaches the current thread from the userland scheduler,
 194  * usually because the thread needs to run in the kernel (at kernel priority)
 195  * for a while.
 196  *
 197  * This routine is also responsible for selecting a new thread to
 198  * make the current thread.
 199  *
 200  * WARNING!  The MP lock may be in an unsynchronized state due to the
 201  * way get_mplock() works and the fact that this function may be called
 202  * from a passive release during a lwkt_switch().   try_mplock() will deal
 203  * with this for us but you should be aware that td_mpcount may not be
 204  * useable.
 205  *
 206  * MPSAFE
 207  */
 208 static void
 209 dummy_release_curproc(struct lwp *lp)
 210 {
 211         globaldata_t gd = mycpu;
 212         dummy_pcpu_t dd = &dummy_pcpu[gd->gd_cpuid];
 213
 214         KKASSERT((lp->lwp_flag & LWP_ONRUNQ) == 0);
 215         if (dd->uschedcp == lp) {
 216                 dummy_select_curproc(gd);
 217         }
 218 }
 219
 220 /*
 221  * DUMMY_SELECT_CURPROC
 222  *
 223  * Select a new current process for this cpu.  This satisfies a user
 224  * scheduler reschedule request so clear that too.
 225  *
 226  * This routine is also responsible for equal-priority round-robining,
 227  * typically triggered from dummy_schedulerclock().  In our dummy example
 228  * all the 'user' threads are LWKT scheduled all at once and we just
 229  * call lwkt_switch().
 230  *
 231  * MPSAFE
 232  */
 233 static
 234 void
 235 dummy_select_curproc(globaldata_t gd)
 236 {
 237         dummy_pcpu_t dd = &dummy_pcpu[gd->gd_cpuid];
 238         struct lwp *lp;
 239
 240         clear_user_resched();
 241         spin_lock_wr(&dummy_spin);
 242         if ((lp = TAILQ_FIRST(&dummy_runq)) == NULL) {
 243                 dd->uschedcp = NULL;
 244                 atomic_clear_int(&dummy_curprocmask, gd->gd_cpumask);
 245                 spin_unlock_wr(&dummy_spin);
 246         } else {
 247                 --dummy_runqcount;
 248                 TAILQ_REMOVE(&dummy_runq, lp, lwp_procq);
 249                 lp->lwp_flag &= ~LWP_ONRUNQ;
 250                 dd->uschedcp = lp;
 251                 atomic_set_int(&dummy_curprocmask, gd->gd_cpumask);
 252                 spin_unlock_wr(&dummy_spin);
 253 #ifdef SMP
 254                 lwkt_acquire(lp->lwp_thread);
 255 #endif
 256                 lwkt_schedule(lp->lwp_thread);
 257         }
 258 }
 259
 260 /*
 261  * DUMMY_SETRUNQUEUE
 262  *
 263  * This routine is called to schedule a new user process after a fork.
 264  * The scheduler module itself might also call this routine to place
 265  * the current process on the userland scheduler's run queue prior
 266  * to calling dummy_select_curproc().
 267  *
 268  * The caller may set P_PASSIVE_ACQ in p_flag to indicate that we should
 269  * attempt to leave the thread on the current cpu.
 270  *
 271  * MPSAFE
 272  */
 273 static void
 274 dummy_setrunqueue(struct lwp *lp)
 275 {
 276         globaldata_t gd = mycpu;
 277         dummy_pcpu_t dd = &dummy_pcpu[gd->gd_cpuid];
 278         cpumask_t mask;
 279         int cpuid;
 280
 281         if (dd->uschedcp == NULL) {
 282                 dd->uschedcp = lp;
 283                 atomic_set_int(&dummy_curprocmask, gd->gd_cpumask);
 284                 lwkt_schedule(lp->lwp_thread);
 285         } else {
 286                 /*
 287                  * Add to our global runq
 288                  */
 289                 KKASSERT((lp->lwp_flag & LWP_ONRUNQ) == 0);
 290                 spin_lock_wr(&dummy_spin);
 291                 ++dummy_runqcount;
 292                 TAILQ_INSERT_TAIL(&dummy_runq, lp, lwp_procq);
 293                 lp->lwp_flag |= LWP_ONRUNQ;
 294 #ifdef SMP
 295                 lwkt_giveaway(lp->lwp_thread);
 296 #endif
 297
 298                 /* lp = TAILQ_FIRST(&dummy_runq); */
 299
 300                 /*
 301                  * Notify the next available cpu.  P.S. some
 302                  * cpu affinity could be done here.
 303                  *
 304                  * The rdyprocmask bit placeholds the knowledge that there
 305                  * is a process on the runq that needs service.  If the
 306                  * helper thread cannot find a home for it it will forward
 307                  * the request to another available cpu.
 308                  */
 309                 mask = ~dummy_curprocmask & dummy_rdyprocmask &
 310                        gd->gd_other_cpus;
 311                 if (mask) {
 312                         cpuid = bsfl(mask);
 313                         atomic_clear_int(&dummy_rdyprocmask, 1 << cpuid);
 314                         spin_unlock_wr(&dummy_spin);
 315                         lwkt_schedule(&dummy_pcpu[cpuid].helper_thread);
 316                 } else {
 317                         spin_unlock_wr(&dummy_spin);
 318                 }
 319         }
 320 }
 321
 322 /*
 323  * This routine is called from a systimer IPI.  Thus it is called with
 324  * a critical section held.  Any spinlocks we get here that are also
 325  * obtained in other procedures must be proected by a critical section
 326  * in those other procedures to avoid a deadlock.
 327  *
 328  * The MP lock may or may not be held on entry and cannot be obtained
 329  * by this routine (because it is called from a systimer IPI).  Additionally,
 330  * because this is equivalent to a FAST interrupt, spinlocks cannot be used
 331  * (or at least, you have to check that gd_spin* counts are 0 before you
 332  * can).
 333  *
 334  * This routine is called at ESTCPUFREQ on each cpu independantly.
 335  *
 336  * This routine typically queues a reschedule request, which will cause
 337  * the scheduler's BLAH_select_curproc() to be called as soon as possible.
 338  *
 339  * MPSAFE
 340  */
 341 static
 342 void
 343 dummy_schedulerclock(struct lwp *lp, sysclock_t period, sysclock_t cpstamp)
 344 {
 345         globaldata_t gd = mycpu;
 346         dummy_pcpu_t dd = &dummy_pcpu[gd->gd_cpuid];
 347
 348         if (++dd->rrcount >= usched_dummy_rrinterval) {
 349                 dd->rrcount = 0;
 350                 need_user_resched();
 351         }
 352 }
 353
 354 /*
 355  * DUMMY_RECALCULATE_ESTCPU
 356  *
 357  * Called once a second for any process that is running or has slept
 358  * for less then 2 seconds.
 359  *
 360  * MPSAFE
 361  */
 362 static
 363 void
 364 dummy_recalculate_estcpu(struct lwp *lp)
 365 {
 366 }
 367
 368 /*
 369  * MPSAFE
 370  */
 371 static
 372 void
 373 dummy_yield(struct lwp *lp)
 374 {
 375         need_user_resched();
 376 }
 377
 378 /*
 379  * DUMMY_RESETPRIORITY
 380  *
 381  * This routine is called after the kernel has potentially modified
 382  * the lwp_rtprio structure.  The target process may be running or sleeping
 383  * or scheduled but not yet running or owned by another cpu.  Basically,
 384  * it can be in virtually any state.
 385  *
 386  * This routine is called by fork1() for initial setup with the process
 387  * of the run queue, and also may be called normally with the process on or
 388  * off the run queue.
 389  *
 390  * MPSAFE
 391  */
 392 static void
 393 dummy_resetpriority(struct lwp *lp)
 394 {
 395         /* XXX spinlock usually needed */
 396         /*
 397          * Set p_priority for general process comparisons
 398          */
 399         switch(lp->lwp_rtprio.type) {
 400         case RTP_PRIO_REALTIME:
 401                 lp->lwp_priority = PRIBASE_REALTIME + lp->lwp_rtprio.prio;
 402                 return;
 403         case RTP_PRIO_NORMAL:
 404                 lp->lwp_priority = PRIBASE_NORMAL + lp->lwp_rtprio.prio;
 405                 break;
 406         case RTP_PRIO_IDLE:
 407                 lp->lwp_priority = PRIBASE_IDLE + lp->lwp_rtprio.prio;
 408                 return;
 409         case RTP_PRIO_THREAD:
 410                 lp->lwp_priority = PRIBASE_THREAD + lp->lwp_rtprio.prio;
 411                 return;
 412         }
 413         /* XXX spinlock usually needed */
 414 }
 415
 416
 417 /*
 418  * DUMMY_FORKING
 419  *
 420  * Called from fork1() when a new child process is being created.  Allows
 421  * the scheduler to predispose the child process before it gets scheduled.
 422  *
 423  * MPSAFE
 424  */
 425 static void
 426 dummy_forking(struct lwp *plp, struct lwp *lp)
 427 {
 428         lp->lwp_estcpu = plp->lwp_estcpu;
 429 #if 0
 430         ++plp->lwp_estcpu;
 431 #endif
 432 }
 433
 434 /*
 435  * DUMMY_EXITING
 436  *
 437  * Called when the parent reaps a child.   Typically used to propogate cpu
 438  * use by the child back to the parent as part of a batch detection
 439  * heuristic.
 440  *
 441  * NOTE: cpu use is not normally back-propogated to PID 1.
 442  *
 443  * MPSAFE
 444  */
 445 static void
 446 dummy_exiting(struct lwp *plp, struct lwp *lp)
 447 {
 448 }
 449
 450 /*
 451  * SMP systems may need a scheduler helper thread.  This is how one can be
 452  * setup.
 453  *
 454  * We use a neat LWKT scheduling trick to interlock the helper thread.  It
 455  * is possible to deschedule an LWKT thread and then do some work before
 456  * switching away.  The thread can be rescheduled at any time, even before
 457  * we switch away.
 458  */
 459 #ifdef SMP
 460
 461 static void
 462 dummy_sched_thread(void *dummy)
 463 {
 464     globaldata_t gd;
 465     dummy_pcpu_t dd;
 466     struct lwp *lp;
 467     cpumask_t cpumask;
 468     cpumask_t tmpmask;
 469     int cpuid;
 470     int tmpid;
 471
 472     gd = mycpu;
 473     cpuid = gd->gd_cpuid;
 474     dd = &dummy_pcpu[cpuid];
 475     cpumask = 1 << cpuid;
 476
 477     /*
 478      * Our Scheduler helper thread does not need to hold the MP lock
 479      */
 480     rel_mplock();
 481
 482     for (;;) {
 483         lwkt_deschedule_self(gd->gd_curthread);         /* interlock */
 484         atomic_set_int(&dummy_rdyprocmask, cpumask);
 485         spin_lock_wr(&dummy_spin);
 486         if (dd->uschedcp) {
 487                 /*
 488                  * We raced another cpu trying to schedule a thread onto us.
 489                  * If the runq isn't empty hit another free cpu.
 490                  */
 491                 tmpmask = ~dummy_curprocmask & dummy_rdyprocmask &
 492                           gd->gd_other_cpus;
 493                 if (tmpmask && dummy_runqcount) {
 494                         tmpid = bsfl(tmpmask);
 495                         KKASSERT(tmpid != cpuid);
 496                         atomic_clear_int(&dummy_rdyprocmask, 1 << tmpid);
 497                         spin_unlock_wr(&dummy_spin);
 498                         lwkt_schedule(&dummy_pcpu[tmpid].helper_thread);
 499                 } else {
 500                         spin_unlock_wr(&dummy_spin);
 501                 }
 502         } else if ((lp = TAILQ_FIRST(&dummy_runq)) != NULL) {
 503                 --dummy_runqcount;
 504                 TAILQ_REMOVE(&dummy_runq, lp, lwp_procq);
 505                 lp->lwp_flag &= ~LWP_ONRUNQ;
 506                 dd->uschedcp = lp;
 507                 atomic_set_int(&dummy_curprocmask, cpumask);
 508                 spin_unlock_wr(&dummy_spin);
 509 #ifdef SMP
 510                 lwkt_acquire(lp->lwp_thread);
 511 #endif
 512                 lwkt_schedule(lp->lwp_thread);
 513         } else {
 514                 spin_unlock_wr(&dummy_spin);
 515         }
 516         lwkt_switch();
 517     }
 518 }
 519
 520 /*
 521  * Setup our scheduler helpers.  Note that curprocmask bit 0 has already
 522  * been cleared by rqinit() and we should not mess with it further.
 523  */
 524 static void
 525 dummy_sched_thread_cpu_init(void)
 526 {
 527     int i;
 528
 529     if (bootverbose)
 530         kprintf("start dummy scheduler helpers on cpus:");
 531
 532     for (i = 0; i < ncpus; ++i) {
 533         dummy_pcpu_t dd = &dummy_pcpu[i];
 534         cpumask_t mask = 1 << i;
 535
 536         if ((mask & smp_active_mask) == 0)
 537             continue;
 538
 539         if (bootverbose)
 540             kprintf(" %d", i);
 541
 542         lwkt_create(dummy_sched_thread, NULL, NULL, &dd->helper_thread,
 543                     TDF_STOPREQ, i, "dsched %d", i);
 544
 545         /*
 546          * Allow user scheduling on the target cpu.  cpu #0 has already
 547          * been enabled in rqinit().
 548          */
 549         if (i)
 550             atomic_clear_int(&dummy_curprocmask, mask);
 551         atomic_set_int(&dummy_rdyprocmask, mask);
 552     }
 553     if (bootverbose)
 554         kprintf("\n");
 555 }
 556 SYSINIT(uschedtd, SI_BOOT2_USCHED, SI_ORDER_SECOND,
 557         dummy_sched_thread_cpu_init, NULL)
 558
 559 #endif
 560