/*- * Copyright (c) 2001 Jake Burkholder * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ #include __FBSDID("$FreeBSD$"); #include "opt_sched.h" #include #include #include #include #include #include #include #include #include #include #include #include #include /* Uncomment this to enable logging of critical_enter/exit. */ #if 0 #define KTR_CRITICAL KTR_SCHED #else #define KTR_CRITICAL 0 #endif #ifdef FULL_PREEMPTION #ifndef PREEMPTION #error "The FULL_PREEMPTION option requires the PREEMPTION option" #endif #endif CTASSERT((RQB_BPW * RQB_LEN) == RQ_NQS); /* * kern.sched.preemption allows user space to determine if preemption support * is compiled in or not. It is not currently a boot or runtime flag that * can be changed. */ #ifdef PREEMPTION static int kern_sched_preemption = 1; #else static int kern_sched_preemption = 0; #endif SYSCTL_INT(_kern_sched, OID_AUTO, preemption, CTLFLAG_RD, &kern_sched_preemption, 0, "Kernel preemption enabled"); /* * Support for scheduler stats exported via kern.sched.stats. All stats may * be reset with kern.sched.stats.reset = 1. Stats may be defined elsewhere * with SCHED_STAT_DEFINE(). */ #ifdef SCHED_STATS SYSCTL_NODE(_kern_sched, OID_AUTO, stats, CTLFLAG_RW, 0, "switch stats"); /* Switch reasons from mi_switch(). */ DPCPU_DEFINE(long, sched_switch_stats[SWT_COUNT]); SCHED_STAT_DEFINE_VAR(uncategorized, &DPCPU_NAME(sched_switch_stats[SWT_NONE]), ""); SCHED_STAT_DEFINE_VAR(preempt, &DPCPU_NAME(sched_switch_stats[SWT_PREEMPT]), ""); SCHED_STAT_DEFINE_VAR(owepreempt, &DPCPU_NAME(sched_switch_stats[SWT_OWEPREEMPT]), ""); SCHED_STAT_DEFINE_VAR(turnstile, &DPCPU_NAME(sched_switch_stats[SWT_TURNSTILE]), ""); SCHED_STAT_DEFINE_VAR(sleepq, &DPCPU_NAME(sched_switch_stats[SWT_SLEEPQ]), ""); SCHED_STAT_DEFINE_VAR(sleepqtimo, &DPCPU_NAME(sched_switch_stats[SWT_SLEEPQTIMO]), ""); SCHED_STAT_DEFINE_VAR(relinquish, &DPCPU_NAME(sched_switch_stats[SWT_RELINQUISH]), ""); SCHED_STAT_DEFINE_VAR(needresched, &DPCPU_NAME(sched_switch_stats[SWT_NEEDRESCHED]), ""); SCHED_STAT_DEFINE_VAR(idle, &DPCPU_NAME(sched_switch_stats[SWT_IDLE]), ""); SCHED_STAT_DEFINE_VAR(iwait, &DPCPU_NAME(sched_switch_stats[SWT_IWAIT]), ""); SCHED_STAT_DEFINE_VAR(suspend, &DPCPU_NAME(sched_switch_stats[SWT_SUSPEND]), ""); SCHED_STAT_DEFINE_VAR(remotepreempt, &DPCPU_NAME(sched_switch_stats[SWT_REMOTEPREEMPT]), ""); SCHED_STAT_DEFINE_VAR(remotewakeidle, &DPCPU_NAME(sched_switch_stats[SWT_REMOTEWAKEIDLE]), ""); static int sysctl_stats_reset(SYSCTL_HANDLER_ARGS) { struct sysctl_oid *p; uintptr_t counter; int error; int val; int i; val = 0; error = sysctl_handle_int(oidp, &val, 0, req); if (error != 0 || req->newptr == NULL) return (error); if (val == 0) return (0); /* * Traverse the list of children of _kern_sched_stats and reset each * to 0. Skip the reset entry. */ SLIST_FOREACH(p, oidp->oid_parent, oid_link) { if (p == oidp || p->oid_arg1 == NULL) continue; counter = (uintptr_t)p->oid_arg1; CPU_FOREACH(i) { *(long *)(dpcpu_off[i] + counter) = 0; } } return (0); } SYSCTL_PROC(_kern_sched_stats, OID_AUTO, reset, CTLTYPE_INT | CTLFLAG_WR, NULL, 0, sysctl_stats_reset, "I", "Reset scheduler statistics"); #endif /************************************************************************ * Functions that manipulate runnability from a thread perspective. * ************************************************************************/ /* * Select the thread that will be run next. */ struct thread * choosethread(void) { struct thread *td; retry: td = sched_choose(); /* * If we are in panic, only allow system threads, * plus the one we are running in, to be run. */ if (panicstr && ((td->td_proc->p_flag & P_SYSTEM) == 0 && (td->td_flags & TDF_INPANIC) == 0)) { /* note that it is no longer on the run queue */ TD_SET_CAN_RUN(td); goto retry; } TD_SET_RUNNING(td); return (td); } /* * Kernel thread preemption implementation. Critical sections mark * regions of code in which preemptions are not allowed. * * It might seem a good idea to inline critical_enter() but, in order * to prevent instructions reordering by the compiler, a __compiler_membar() * would have to be used here (the same as sched_pin()). The performance * penalty imposed by the membar could, then, produce slower code than * the function call itself, for most cases. */ void critical_enter(void) { struct thread *td; td = curthread; td->td_critnest++; CTR4(KTR_CRITICAL, "critical_enter by thread %p (%ld, %s) to %d", td, (long)td->td_proc->p_pid, td->td_name, td->td_critnest); } void critical_exit(void) { struct thread *td; int flags; td = curthread; KASSERT(td->td_critnest != 0, ("critical_exit: td_critnest == 0")); if (td->td_critnest == 1) { td->td_critnest = 0; if (td->td_owepreempt && !kdb_active) { td->td_critnest = 1; thread_lock(td); td->td_critnest--; flags = SW_INVOL | SW_PREEMPT; if (TD_IS_IDLETHREAD(td)) flags |= SWT_IDLE; else flags |= SWT_OWEPREEMPT; mi_switch(flags, NULL); thread_unlock(td); } } else td->td_critnest--; CTR4(KTR_CRITICAL, "critical_exit by thread %p (%ld, %s) to %d", td, (long)td->td_proc->p_pid, td->td_name, td->td_critnest); } /************************************************************************ * SYSTEM RUN QUEUE manipulations and tests * ************************************************************************/ /* * Initialize a run structure. */ void runq_init(struct runq *rq) { int i; bzero(rq, sizeof *rq); for (i = 0; i < RQ_NQS; i++) TAILQ_INIT(&rq->rq_queues[i]); } /* * Clear the status bit of the queue corresponding to priority level pri, * indicating that it is empty. */ static __inline void runq_clrbit(struct runq *rq, int pri) { struct rqbits *rqb; rqb = &rq->rq_status; CTR4(KTR_RUNQ, "runq_clrbit: bits=%#x %#x bit=%#x word=%d", rqb->rqb_bits[RQB_WORD(pri)], rqb->rqb_bits[RQB_WORD(pri)] & ~RQB_BIT(pri), RQB_BIT(pri), RQB_WORD(pri)); rqb->rqb_bits[RQB_WORD(pri)] &= ~RQB_BIT(pri); } /* * Find the index of the first non-empty run queue. This is done by * scanning the status bits, a set bit indicates a non-empty queue. */ static __inline int runq_findbit(struct runq *rq) { struct rqbits *rqb; int pri; int i; rqb = &rq->rq_status; for (i = 0; i < RQB_LEN; i++) if (rqb->rqb_bits[i]) { pri = RQB_FFS(rqb->rqb_bits[i]) + (i << RQB_L2BPW); CTR3(KTR_RUNQ, "runq_findbit: bits=%#x i=%d pri=%d", rqb->rqb_bits[i], i, pri); return (pri); } return (-1); } static __inline int runq_findbit_from(struct runq *rq, u_char pri) { struct rqbits *rqb; rqb_word_t mask; int i; /* * Set the mask for the first word so we ignore priorities before 'pri'. */ mask = (rqb_word_t)-1 << (pri & (RQB_BPW - 1)); rqb = &rq->rq_status; again: for (i = RQB_WORD(pri); i < RQB_LEN; mask = -1, i++) { mask = rqb->rqb_bits[i] & mask; if (mask == 0) continue; pri = RQB_FFS(mask) + (i << RQB_L2BPW); CTR3(KTR_RUNQ, "runq_findbit_from: bits=%#x i=%d pri=%d", mask, i, pri); return (pri); } if (pri == 0) return (-1); /* * Wrap back around to the beginning of the list just once so we * scan the whole thing. */ pri = 0; goto again; } /* * Set the status bit of the queue corresponding to priority level pri, * indicating that it is non-empty. */ static __inline void runq_setbit(struct runq *rq, int pri) { struct rqbits *rqb; rqb = &rq->rq_status; CTR4(KTR_RUNQ, "runq_setbit: bits=%#x %#x bit=%#x word=%d", rqb->rqb_bits[RQB_WORD(pri)], rqb->rqb_bits[RQB_WORD(pri)] | RQB_BIT(pri), RQB_BIT(pri), RQB_WORD(pri)); rqb->rqb_bits[RQB_WORD(pri)] |= RQB_BIT(pri); } /* * Add the thread to the queue specified by its priority, and set the * corresponding status bit. */ void runq_add(struct runq *rq, struct thread *td, int flags) { struct rqhead *rqh; int pri; pri = td->td_priority / RQ_PPQ; td->td_rqindex = pri; runq_setbit(rq, pri); rqh = &rq->rq_queues[pri]; CTR4(KTR_RUNQ, "runq_add: td=%p pri=%d %d rqh=%p", td, td->td_priority, pri, rqh); if (flags & SRQ_PREEMPTED) { TAILQ_INSERT_HEAD(rqh, td, td_runq); } else { TAILQ_INSERT_TAIL(rqh, td, td_runq); } } void runq_add_pri(struct runq *rq, struct thread *td, u_char pri, int flags) { struct rqhead *rqh; KASSERT(pri < RQ_NQS, ("runq_add_pri: %d out of range", pri)); td->td_rqindex = pri; runq_setbit(rq, pri); rqh = &rq->rq_queues[pri]; CTR4(KTR_RUNQ, "runq_add_pri: td=%p pri=%d idx=%d rqh=%p", td, td->td_priority, pri, rqh); if (flags & SRQ_PREEMPTED) { TAILQ_INSERT_HEAD(rqh, td, td_runq); } else { TAILQ_INSERT_TAIL(rqh, td, td_runq); } } /* * Return true if there are runnable processes of any priority on the run * queue, false otherwise. Has no side effects, does not modify the run * queue structure. */ int runq_check(struct runq *rq) { struct rqbits *rqb; int i; rqb = &rq->rq_status; for (i = 0; i < RQB_LEN; i++) if (rqb->rqb_bits[i]) { CTR2(KTR_RUNQ, "runq_check: bits=%#x i=%d", rqb->rqb_bits[i], i); return (1); } CTR0(KTR_RUNQ, "runq_check: empty"); return (0); } /* * Find the highest priority process on the run queue. */ struct thread * runq_choose_fuzz(struct runq *rq, int fuzz) { struct rqhead *rqh; struct thread *td; int pri; while ((pri = runq_findbit(rq)) != -1) { rqh = &rq->rq_queues[pri]; /* fuzz == 1 is normal.. 0 or less are ignored */ if (fuzz > 1) { /* * In the first couple of entries, check if * there is one for our CPU as a preference. */ int count = fuzz; int cpu = PCPU_GET(cpuid); struct thread *td2; td2 = td = TAILQ_FIRST(rqh); while (count-- && td2) { if (td2->td_lastcpu == cpu) { td = td2; break; } td2 = TAILQ_NEXT(td2, td_runq); } } else td = TAILQ_FIRST(rqh); KASSERT(td != NULL, ("runq_choose_fuzz: no proc on busy queue")); CTR3(KTR_RUNQ, "runq_choose_fuzz: pri=%d thread=%p rqh=%p", pri, td, rqh); return (td); } CTR1(KTR_RUNQ, "runq_choose_fuzz: idleproc pri=%d", pri); return (NULL); } /* * Find the highest priority process on the run queue. */ struct thread * runq_choose(struct runq *rq) { struct rqhead *rqh; struct thread *td; int pri; while ((pri = runq_findbit(rq)) != -1) { rqh = &rq->rq_queues[pri]; td = TAILQ_FIRST(rqh); KASSERT(td != NULL, ("runq_choose: no thread on busy queue")); CTR3(KTR_RUNQ, "runq_choose: pri=%d thread=%p rqh=%p", pri, td, rqh); return (td); } CTR1(KTR_RUNQ, "runq_choose: idlethread pri=%d", pri); return (NULL); } struct thread * runq_choose_from(struct runq *rq, u_char idx) { struct rqhead *rqh; struct thread *td; int pri; if ((pri = runq_findbit_from(rq, idx)) != -1) { rqh = &rq->rq_queues[pri]; td = TAILQ_FIRST(rqh); KASSERT(td != NULL, ("runq_choose: no thread on busy queue")); CTR4(KTR_RUNQ, "runq_choose_from: pri=%d thread=%p idx=%d rqh=%p", pri, td, td->td_rqindex, rqh); return (td); } CTR1(KTR_RUNQ, "runq_choose_from: idlethread pri=%d", pri); return (NULL); } /* * Remove the thread from the queue specified by its priority, and clear the * corresponding status bit if the queue becomes empty. * Caller must set state afterwards. */ void runq_remove(struct runq *rq, struct thread *td) { runq_remove_idx(rq, td, NULL); } void runq_remove_idx(struct runq *rq, struct thread *td, u_char *idx) { struct rqhead *rqh; u_char pri; KASSERT(td->td_flags & TDF_INMEM, ("runq_remove_idx: thread swapped out")); pri = td->td_rqindex; KASSERT(pri < RQ_NQS, ("runq_remove_idx: Invalid index %d\n", pri)); rqh = &rq->rq_queues[pri]; CTR4(KTR_RUNQ, "runq_remove_idx: td=%p, pri=%d %d rqh=%p", td, td->td_priority, pri, rqh); TAILQ_REMOVE(rqh, td, td_runq); if (TAILQ_EMPTY(rqh)) { CTR0(KTR_RUNQ, "runq_remove_idx: empty"); runq_clrbit(rq, pri); if (idx != NULL && *idx == pri) *idx = (pri + 1) % RQ_NQS; } }