/* * Copyright (c) 2003-2010 The DragonFly Project. All rights reserved. * * This code is derived from software contributed to The DragonFly Project * by Matthew Dillon * * 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. * 3. Neither the name of The DragonFly Project nor the names of its * contributors may be used to endorse or promote products derived * from this software without specific, prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 * COPYRIGHT HOLDERS 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. */ /* * Each cpu in a system has its own self-contained light weight kernel * thread scheduler, which means that generally speaking we only need * to use a critical section to avoid problems. Foreign thread * scheduling is queued via (async) IPIs. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #if !defined(KTR_CTXSW) #define KTR_CTXSW KTR_ALL #endif KTR_INFO_MASTER(ctxsw); KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p", sizeof(int) + sizeof(struct thread *)); KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", sizeof(int) + sizeof(struct thread *)); KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", sizeof (struct thread *) + sizeof(char *)); KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = ", sizeof (struct thread *)); static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads"); #ifdef INVARIANTS static int panic_on_cscount = 0; #endif static __int64_t switch_count = 0; static __int64_t preempt_hit = 0; static __int64_t preempt_miss = 0; static __int64_t preempt_weird = 0; static __int64_t token_contention_count __debugvar = 0; static int lwkt_use_spin_port; static struct objcache *thread_cache; #ifdef SMP static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame); #endif static void lwkt_fairq_accumulate(globaldata_t gd, thread_t td); extern void cpu_heavy_restore(void); extern void cpu_lwkt_restore(void); extern void cpu_kthread_restore(void); extern void cpu_idle_restore(void); /* * We can make all thread ports use the spin backend instead of the thread * backend. This should only be set to debug the spin backend. */ TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port); #ifdef INVARIANTS SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0, "Panic if attempting to switch lwkt's while mastering cpusync"); #endif SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0, "Number of switched threads"); SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0, "Successful preemption events"); SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0, "Failed preemption events"); SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0, "Number of preempted threads."); #ifdef INVARIANTS SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count, CTLFLAG_RW, &token_contention_count, 0, "spinning due to token contention"); #endif static int fairq_enable = 1; SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW, &fairq_enable, 0, "Turn on fairq priority accumulators"); static int lwkt_spin_loops = 10; SYSCTL_INT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW, &lwkt_spin_loops, 0, ""); static int lwkt_spin_delay = 1; SYSCTL_INT(_lwkt, OID_AUTO, spin_delay, CTLFLAG_RW, &lwkt_spin_delay, 0, "Scheduler spin delay in microseconds 0=auto"); static int lwkt_spin_method = 1; SYSCTL_INT(_lwkt, OID_AUTO, spin_method, CTLFLAG_RW, &lwkt_spin_method, 0, "LWKT scheduler behavior when contended"); static int lwkt_spin_fatal = 0; /* disabled */ SYSCTL_INT(_lwkt, OID_AUTO, spin_fatal, CTLFLAG_RW, &lwkt_spin_fatal, 0, "LWKT scheduler spin loops till fatal panic"); static int preempt_enable = 1; SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW, &preempt_enable, 0, "Enable preemption"); static __cachealign int lwkt_cseq_rindex; static __cachealign int lwkt_cseq_windex; /* * These helper procedures handle the runq, they can only be called from * within a critical section. * * WARNING! Prior to SMP being brought up it is possible to enqueue and * dequeue threads belonging to other cpus, so be sure to use td->td_gd * instead of 'mycpu' when referencing the globaldata structure. Once * SMP live enqueuing and dequeueing only occurs on the current cpu. */ static __inline void _lwkt_dequeue(thread_t td) { if (td->td_flags & TDF_RUNQ) { struct globaldata *gd = td->td_gd; td->td_flags &= ~TDF_RUNQ; TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq); gd->gd_fairq_total_pri -= td->td_pri; if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL) atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING); } } /* * Priority enqueue. * * NOTE: There are a limited number of lwkt threads runnable since user * processes only schedule one at a time per cpu. */ static __inline void _lwkt_enqueue(thread_t td) { thread_t xtd; if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) { struct globaldata *gd = td->td_gd; td->td_flags |= TDF_RUNQ; xtd = TAILQ_FIRST(&gd->gd_tdrunq); if (xtd == NULL) { TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); atomic_set_int(&gd->gd_reqflags, RQF_RUNNING); } else { while (xtd && xtd->td_pri > td->td_pri) xtd = TAILQ_NEXT(xtd, td_threadq); if (xtd) TAILQ_INSERT_BEFORE(xtd, td, td_threadq); else TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); } gd->gd_fairq_total_pri += td->td_pri; } } static __boolean_t _lwkt_thread_ctor(void *obj, void *privdata, int ocflags) { struct thread *td = (struct thread *)obj; td->td_kstack = NULL; td->td_kstack_size = 0; td->td_flags = TDF_ALLOCATED_THREAD; return (1); } static void _lwkt_thread_dtor(void *obj, void *privdata) { struct thread *td = (struct thread *)obj; KASSERT(td->td_flags & TDF_ALLOCATED_THREAD, ("_lwkt_thread_dtor: not allocated from objcache")); KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack && td->td_kstack_size > 0, ("_lwkt_thread_dtor: corrupted stack")); kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); } /* * Initialize the lwkt s/system. */ void lwkt_init(void) { /* An objcache has 2 magazines per CPU so divide cache size by 2. */ thread_cache = objcache_create_mbacked(M_THREAD, sizeof(struct thread), NULL, CACHE_NTHREADS/2, _lwkt_thread_ctor, _lwkt_thread_dtor, NULL); } /* * Schedule a thread to run. As the current thread we can always safely * schedule ourselves, and a shortcut procedure is provided for that * function. * * (non-blocking, self contained on a per cpu basis) */ void lwkt_schedule_self(thread_t td) { KKASSERT((td->td_flags & TDF_MIGRATING) == 0); crit_enter_quick(td); KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!")); KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); _lwkt_enqueue(td); crit_exit_quick(td); } /* * Deschedule a thread. * * (non-blocking, self contained on a per cpu basis) */ void lwkt_deschedule_self(thread_t td) { crit_enter_quick(td); _lwkt_dequeue(td); crit_exit_quick(td); } /* * LWKTs operate on a per-cpu basis * * WARNING! Called from early boot, 'mycpu' may not work yet. */ void lwkt_gdinit(struct globaldata *gd) { TAILQ_INIT(&gd->gd_tdrunq); TAILQ_INIT(&gd->gd_tdallq); } /* * Create a new thread. The thread must be associated with a process context * or LWKT start address before it can be scheduled. If the target cpu is * -1 the thread will be created on the current cpu. * * If you intend to create a thread without a process context this function * does everything except load the startup and switcher function. */ thread_t lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags) { globaldata_t gd = mycpu; void *stack; /* * If static thread storage is not supplied allocate a thread. Reuse * a cached free thread if possible. gd_freetd is used to keep an exiting * thread intact through the exit. */ if (td == NULL) { crit_enter_gd(gd); if ((td = gd->gd_freetd) != NULL) { KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK| TDF_RUNQ)) == 0); gd->gd_freetd = NULL; } else { td = objcache_get(thread_cache, M_WAITOK); KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK| TDF_RUNQ)) == 0); } crit_exit_gd(gd); KASSERT((td->td_flags & (TDF_ALLOCATED_THREAD|TDF_RUNNING)) == TDF_ALLOCATED_THREAD, ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags)); flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK); } /* * Try to reuse cached stack. */ if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) { if (flags & TDF_ALLOCATED_STACK) { kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size); stack = NULL; } } if (stack == NULL) { stack = (void *)kmem_alloc_stack(&kernel_map, stksize); flags |= TDF_ALLOCATED_STACK; } if (cpu < 0) lwkt_init_thread(td, stack, stksize, flags, gd); else lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu)); return(td); } /* * Initialize a preexisting thread structure. This function is used by * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread. * * All threads start out in a critical section at a priority of * TDPRI_KERN_DAEMON. Higher level code will modify the priority as * appropriate. This function may send an IPI message when the * requested cpu is not the current cpu and consequently gd_tdallq may * not be initialized synchronously from the point of view of the originating * cpu. * * NOTE! we have to be careful in regards to creating threads for other cpus * if SMP has not yet been activated. */ #ifdef SMP static void lwkt_init_thread_remote(void *arg) { thread_t td = arg; /* * Protected by critical section held by IPI dispatch */ TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq); } #endif /* * lwkt core thread structural initialization. * * NOTE: All threads are initialized as mpsafe threads. */ void lwkt_init_thread(thread_t td, void *stack, int stksize, int flags, struct globaldata *gd) { globaldata_t mygd = mycpu; bzero(td, sizeof(struct thread)); td->td_kstack = stack; td->td_kstack_size = stksize; td->td_flags = flags; td->td_gd = gd; td->td_pri = TDPRI_KERN_DAEMON; td->td_critcount = 1; td->td_toks_stop = &td->td_toks_base; if (lwkt_use_spin_port) lwkt_initport_spin(&td->td_msgport); else lwkt_initport_thread(&td->td_msgport, td); pmap_init_thread(td); #ifdef SMP /* * Normally initializing a thread for a remote cpu requires sending an * IPI. However, the idlethread is setup before the other cpus are * activated so we have to treat it as a special case. XXX manipulation * of gd_tdallq requires the BGL. */ if (gd == mygd || td == &gd->gd_idlethread) { crit_enter_gd(mygd); TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); crit_exit_gd(mygd); } else { lwkt_send_ipiq(gd, lwkt_init_thread_remote, td); } #else crit_enter_gd(mygd); TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); crit_exit_gd(mygd); #endif dsched_new_thread(td); } void lwkt_set_comm(thread_t td, const char *ctl, ...) { __va_list va; __va_start(va, ctl); kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va); __va_end(va); KTR_LOG(ctxsw_newtd, td, &td->td_comm[0]); } void lwkt_hold(thread_t td) { atomic_add_int(&td->td_refs, 1); } void lwkt_rele(thread_t td) { KKASSERT(td->td_refs > 0); atomic_add_int(&td->td_refs, -1); } void lwkt_wait_free(thread_t td) { while (td->td_refs) tsleep(td, 0, "tdreap", hz); } void lwkt_free_thread(thread_t td) { KKASSERT(td->td_refs == 0); KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|TDF_RUNQ)) == 0); if (td->td_flags & TDF_ALLOCATED_THREAD) { objcache_put(thread_cache, td); } else if (td->td_flags & TDF_ALLOCATED_STACK) { /* client-allocated struct with internally allocated stack */ KASSERT(td->td_kstack && td->td_kstack_size > 0, ("lwkt_free_thread: corrupted stack")); kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); td->td_kstack = NULL; td->td_kstack_size = 0; } KTR_LOG(ctxsw_deadtd, td); } /* * Switch to the next runnable lwkt. If no LWKTs are runnable then * switch to the idlethread. Switching must occur within a critical * section to avoid races with the scheduling queue. * * We always have full control over our cpu's run queue. Other cpus * that wish to manipulate our queue must use the cpu_*msg() calls to * talk to our cpu, so a critical section is all that is needed and * the result is very, very fast thread switching. * * The LWKT scheduler uses a fixed priority model and round-robins at * each priority level. User process scheduling is a totally * different beast and LWKT priorities should not be confused with * user process priorities. * * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch() * is not called by the current thread in the preemption case, only when * the preempting thread blocks (in order to return to the original thread). * * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread * migration and tsleep deschedule the current lwkt thread and call * lwkt_switch(). In particular, the target cpu of the migration fully * expects the thread to become non-runnable and can deadlock against * cpusync operations if we run any IPIs prior to switching the thread out. * * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF * THE CURRENT THREAD HAS BEEN DESCHEDULED! */ void lwkt_switch(void) { globaldata_t gd = mycpu; thread_t td = gd->gd_curthread; thread_t ntd; thread_t xtd; int spinning = lwkt_spin_loops; /* loops before HLTing */ int reqflags; int cseq; int oseq; int fatal_count; /* * Switching from within a 'fast' (non thread switched) interrupt or IPI * is illegal. However, we may have to do it anyway if we hit a fatal * kernel trap or we have paniced. * * If this case occurs save and restore the interrupt nesting level. */ if (gd->gd_intr_nesting_level) { int savegdnest; int savegdtrap; if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) { panic("lwkt_switch: Attempt to switch from a " "a fast interrupt, ipi, or hard code section, " "td %p\n", td); } else { savegdnest = gd->gd_intr_nesting_level; savegdtrap = gd->gd_trap_nesting_level; gd->gd_intr_nesting_level = 0; gd->gd_trap_nesting_level = 0; if ((td->td_flags & TDF_PANICWARN) == 0) { td->td_flags |= TDF_PANICWARN; kprintf("Warning: thread switch from interrupt, IPI, " "or hard code section.\n" "thread %p (%s)\n", td, td->td_comm); print_backtrace(-1); } lwkt_switch(); gd->gd_intr_nesting_level = savegdnest; gd->gd_trap_nesting_level = savegdtrap; return; } } /* * Passive release (used to transition from user to kernel mode * when we block or switch rather then when we enter the kernel). * This function is NOT called if we are switching into a preemption * or returning from a preemption. Typically this causes us to lose * our current process designation (if we have one) and become a true * LWKT thread, and may also hand the current process designation to * another process and schedule thread. */ if (td->td_release) td->td_release(td); crit_enter_gd(gd); if (TD_TOKS_HELD(td)) lwkt_relalltokens(td); /* * We had better not be holding any spin locks, but don't get into an * endless panic loop. */ KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL, ("lwkt_switch: still holding %d exclusive spinlocks!", gd->gd_spinlocks_wr)); #ifdef SMP #ifdef INVARIANTS if (td->td_cscount) { kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n", td); if (panic_on_cscount) panic("switching while mastering cpusync"); } #endif #endif /* * If we had preempted another thread on this cpu, resume the preempted * thread. This occurs transparently, whether the preempted thread * was scheduled or not (it may have been preempted after descheduling * itself). * * We have to setup the MP lock for the original thread after backing * out the adjustment that was made to curthread when the original * was preempted. */ if ((ntd = td->td_preempted) != NULL) { KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK); ntd->td_flags |= TDF_PREEMPT_DONE; /* * The interrupt may have woken a thread up, we need to properly * set the reschedule flag if the originally interrupted thread is * at a lower priority. */ if (TAILQ_FIRST(&gd->gd_tdrunq) && TAILQ_FIRST(&gd->gd_tdrunq)->td_pri > ntd->td_pri) { need_lwkt_resched(); } /* YYY release mp lock on switchback if original doesn't need it */ goto havethread_preempted; } /* * Implement round-robin fairq with priority insertion. The priority * insertion is handled by _lwkt_enqueue() * * If we cannot obtain ownership of the tokens we cannot immediately * schedule the target thread. * * Reminder: Again, we cannot afford to run any IPIs in this path if * the current thread has been descheduled. */ for (;;) { /* * Clear RQF_AST_LWKT_RESCHED (we handle the reschedule request) * and set RQF_WAKEUP (prevent unnecessary IPIs from being * received). */ for (;;) { reqflags = gd->gd_reqflags; if (atomic_cmpset_int(&gd->gd_reqflags, reqflags, (reqflags & ~RQF_AST_LWKT_RESCHED) | RQF_WAKEUP)) { break; } } /* * Hotpath - pull the head of the run queue and attempt to schedule * it. Fairq exhaustion moves the task to the end of the list. If * no threads are runnable we switch to the idle thread. */ for (;;) { ntd = TAILQ_FIRST(&gd->gd_tdrunq); if (ntd == NULL) { /* * Runq is empty, switch to idle and clear RQF_WAKEUP * to allow it to halt. */ ntd = &gd->gd_idlethread; #ifdef SMP if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) ASSERT_NO_TOKENS_HELD(ntd); #endif cpu_time.cp_msg[0] = 0; cpu_time.cp_stallpc = 0; atomic_clear_int(&gd->gd_reqflags, RQF_WAKEUP); goto haveidle; } if (ntd->td_fairq_accum >= 0) break; /*splz_check(); cannot do this here, see above */ lwkt_fairq_accumulate(gd, ntd); TAILQ_REMOVE(&gd->gd_tdrunq, ntd, td_threadq); TAILQ_INSERT_TAIL(&gd->gd_tdrunq, ntd, td_threadq); } /* * Hotpath - schedule ntd. Leaves RQF_WAKEUP set to prevent * unwanted decontention IPIs. * * NOTE: For UP there is no mplock and lwkt_getalltokens() * always succeeds. */ if (TD_TOKS_NOT_HELD(ntd) || lwkt_getalltokens(ntd)) goto havethread; /* * Coldpath (SMP only since tokens always succeed on UP) * * We had some contention on the thread we wanted to schedule. * What we do now is try to find a thread that we can schedule * in its stead until decontention reschedules on our cpu. * * The coldpath scan does NOT rearrange threads in the run list * and it also ignores the accumulator. * * We do not immediately schedule a user priority thread, instead * we record it in xtd and continue looking for kernel threads. * A cpu can only have one user priority thread (normally) so just * record the first one. * * NOTE: This scan will also include threads whos fairq's were * accumulated in the first loop. */ ++token_contention_count; xtd = NULL; while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) { /* * Try to switch to this thread. If the thread is running at * user priority we clear WAKEUP to allow decontention IPIs * (since this thread is simply running until the one we wanted * decontends), and we make sure that LWKT_RESCHED is not set. * * Otherwise for kernel threads we leave WAKEUP set to avoid * unnecessary decontention IPIs. */ if (ntd->td_pri < TDPRI_KERN_LPSCHED) { if (xtd == NULL) xtd = ntd; continue; } /* * Do not let the fairq get too negative. Even though we are * ignoring it atm once the scheduler decontends a very negative * thread will get moved to the end of the queue. */ if (TD_TOKS_NOT_HELD(ntd) || lwkt_getalltokens(ntd)) { if (ntd->td_fairq_accum < -TDFAIRQ_MAX(gd)) ntd->td_fairq_accum = -TDFAIRQ_MAX(gd); goto havethread; } /* * Well fubar, this thread is contended as well, loop */ /* */ } /* * We exhausted the run list but we may have recorded a user * thread to try. We have three choices based on * lwkt.decontention_method. * * (0) Atomically clear RQF_WAKEUP in order to receive decontention * IPIs (to interrupt the user process) and test * RQF_AST_LWKT_RESCHED at the same time. * * This results in significant decontention IPI traffic but may * be more responsive. * * (1) Leave RQF_WAKEUP set so we do not receive a decontention IPI. * An automatic LWKT reschedule will occur on the next hardclock * (typically 100hz). * * This results in no decontention IPI traffic but may be less * responsive. This is the default. * * (2) Refuse to schedule the user process at this time. * * This is highly experimental and should not be used under * normal circumstances. This can cause a user process to * get starved out in situations where kernel threads are * fighting each other for tokens. */ if (xtd) { ntd = xtd; switch(lwkt_spin_method) { case 0: for (;;) { reqflags = gd->gd_reqflags; if (atomic_cmpset_int(&gd->gd_reqflags, reqflags, reqflags & ~RQF_WAKEUP)) { break; } } break; case 1: reqflags = gd->gd_reqflags; break; default: goto skip; break; } if ((reqflags & RQF_AST_LWKT_RESCHED) == 0 && (TD_TOKS_NOT_HELD(ntd) || lwkt_getalltokens(ntd)) ) { if (ntd->td_fairq_accum < -TDFAIRQ_MAX(gd)) ntd->td_fairq_accum = -TDFAIRQ_MAX(gd); goto havethread; } skip: /* * Make sure RQF_WAKEUP is set if we failed to schedule the * user thread to prevent the idle thread from halting. */ atomic_set_int(&gd->gd_reqflags, RQF_WAKEUP); } /* * We exhausted the run list, meaning that all runnable threads * are contended. */ cpu_pause(); ntd = &gd->gd_idlethread; #ifdef SMP if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) ASSERT_NO_TOKENS_HELD(ntd); /* contention case, do not clear contention mask */ #endif /* * Ok, we might want to spin a few times as some tokens are held for * very short periods of time and IPI overhead is 1uS or worse * (meaning it is usually better to spin). Regardless we have to * call splz_check() to be sure to service any interrupts blocked * by our critical section, otherwise we could livelock e.g. IPIs. * * The IPI mechanic is really a last resort. In nearly all other * cases RQF_WAKEUP is left set to prevent decontention IPIs. * * When we decide not to spin we clear RQF_WAKEUP and switch to * the idle thread. Clearing RQF_WEAKEUP allows the idle thread * to halt and decontended tokens will issue an IPI to us. The * idle thread will check for pending reschedules already set * (RQF_AST_LWKT_RESCHED) before actually halting so we don't have * to here. * * Also, if TDF_RUNQ is not set the current thread is trying to * deschedule, possibly in an atomic fashion. We cannot afford to * stay here. */ if (spinning <= 0 || (td->td_flags & TDF_RUNQ) == 0) { atomic_clear_int(&gd->gd_reqflags, RQF_WAKEUP); goto haveidle; } --spinning; /* * When spinning a delay is required both to avoid livelocks from * token order reversals (a thread may be trying to acquire multiple * tokens), and also to reduce cpu cache management traffic. * * In order to scale to a large number of CPUs we use a time slot * resequencer to force contending cpus into non-contending * time-slots. The scheduler may still contend with the lock holder * but will not (generally) contend with all the other cpus trying * trying to get the same token. * * The resequencer uses a FIFO counter mechanic. The owner of the * rindex at the head of the FIFO is allowed to pull itself off * the FIFO and fetchadd is used to enter into the FIFO. This bit * of code is VERY cache friendly and forces all spinning schedulers * into their own time slots. * * This code has been tested to 48-cpus and caps the cache * contention load at ~1uS intervals regardless of the number of * cpus. Scaling beyond 64 cpus might require additional smarts * (such as separate FIFOs for specific token cases). * * WARNING! We can't call splz_check() or anything else here as * it could cause a deadlock. */ #if defined(INVARIANTS) && defined(__amd64__) if ((read_rflags() & PSL_I) == 0) { cpu_enable_intr(); panic("lwkt_switch() called with interrupts disabled"); } #endif cseq = atomic_fetchadd_int(&lwkt_cseq_windex, 1); fatal_count = lwkt_spin_fatal; while ((oseq = lwkt_cseq_rindex) != cseq) { cpu_ccfence(); #if !defined(_KERNEL_VIRTUAL) if (cpu_mi_feature & CPU_MI_MONITOR) { cpu_mmw_pause_int(&lwkt_cseq_rindex, oseq); } else #endif { DELAY(1); cpu_lfence(); } if (fatal_count && --fatal_count == 0) panic("lwkt_switch: fatal spin wait"); } cseq = lwkt_spin_delay; /* don't trust the system operator */ cpu_ccfence(); if (cseq < 1) cseq = 1; if (cseq > 1000) cseq = 1000; DELAY(cseq); atomic_add_int(&lwkt_cseq_rindex, 1); splz_check(); /* ok, we already checked that td is still scheduled */ /* highest level for(;;) loop */ } havethread: /* * We must always decrement td_fairq_accum on non-idle threads just * in case a thread never gets a tick due to being in a continuous * critical section. The page-zeroing code does this, for example. * * If the thread we came up with is a higher or equal priority verses * the thread at the head of the queue we move our thread to the * front. This way we can always check the front of the queue. * * Clear gd_idle_repeat when doing a normal switch to a non-idle * thread. */ ++gd->gd_cnt.v_swtch; --ntd->td_fairq_accum; ntd->td_wmesg = NULL; xtd = TAILQ_FIRST(&gd->gd_tdrunq); if (ntd != xtd && ntd->td_pri >= xtd->td_pri) { TAILQ_REMOVE(&gd->gd_tdrunq, ntd, td_threadq); TAILQ_INSERT_HEAD(&gd->gd_tdrunq, ntd, td_threadq); } gd->gd_idle_repeat = 0; havethread_preempted: /* * If the new target does not need the MP lock and we are holding it, * release the MP lock. If the new target requires the MP lock we have * already acquired it for the target. */ ; haveidle: KASSERT(ntd->td_critcount, ("priority problem in lwkt_switch %d %d", td->td_critcount, ntd->td_critcount)); if (td != ntd) { ++switch_count; KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd); td->td_switch(ntd); } /* NOTE: current cpu may have changed after switch */ crit_exit_quick(td); } /* * Request that the target thread preempt the current thread. Preemption * only works under a specific set of conditions: * * - We are not preempting ourselves * - The target thread is owned by the current cpu * - We are not currently being preempted * - The target is not currently being preempted * - We are not holding any spin locks * - The target thread is not holding any tokens * - We are able to satisfy the target's MP lock requirements (if any). * * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically * this is called via lwkt_schedule() through the td_preemptable callback. * critcount is the managed critical priority that we should ignore in order * to determine whether preemption is possible (aka usually just the crit * priority of lwkt_schedule() itself). * * XXX at the moment we run the target thread in a critical section during * the preemption in order to prevent the target from taking interrupts * that *WE* can't. Preemption is strictly limited to interrupt threads * and interrupt-like threads, outside of a critical section, and the * preempted source thread will be resumed the instant the target blocks * whether or not the source is scheduled (i.e. preemption is supposed to * be as transparent as possible). */ void lwkt_preempt(thread_t ntd, int critcount) { struct globaldata *gd = mycpu; thread_t td; int save_gd_intr_nesting_level; /* * The caller has put us in a critical section. We can only preempt * if the caller of the caller was not in a critical section (basically * a local interrupt), as determined by the 'critcount' parameter. We * also can't preempt if the caller is holding any spinlocks (even if * he isn't in a critical section). This also handles the tokens test. * * YYY The target thread must be in a critical section (else it must * inherit our critical section? I dunno yet). * * Set need_lwkt_resched() unconditionally for now YYY. */ KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri)); if (preempt_enable == 0) { ++preempt_miss; return; } td = gd->gd_curthread; if (ntd->td_pri <= td->td_pri) { ++preempt_miss; return; } if (td->td_critcount > critcount) { ++preempt_miss; need_lwkt_resched(); return; } #ifdef SMP if (ntd->td_gd != gd) { ++preempt_miss; need_lwkt_resched(); return; } #endif /* * We don't have to check spinlocks here as they will also bump * td_critcount. * * Do not try to preempt if the target thread is holding any tokens. * We could try to acquire the tokens but this case is so rare there * is no need to support it. */ KKASSERT(gd->gd_spinlocks_wr == 0); if (TD_TOKS_HELD(ntd)) { ++preempt_miss; need_lwkt_resched(); return; } if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) { ++preempt_weird; need_lwkt_resched(); return; } if (ntd->td_preempted) { ++preempt_hit; need_lwkt_resched(); return; } /* * Since we are able to preempt the current thread, there is no need to * call need_lwkt_resched(). * * We must temporarily clear gd_intr_nesting_level around the switch * since switchouts from the target thread are allowed (they will just * return to our thread), and since the target thread has its own stack. */ ++preempt_hit; ntd->td_preempted = td; td->td_flags |= TDF_PREEMPT_LOCK; KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd); save_gd_intr_nesting_level = gd->gd_intr_nesting_level; gd->gd_intr_nesting_level = 0; td->td_switch(ntd); gd->gd_intr_nesting_level = save_gd_intr_nesting_level; KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE)); ntd->td_preempted = NULL; td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE); } /* * Conditionally call splz() if gd_reqflags indicates work is pending. * This will work inside a critical section but not inside a hard code * section. * * (self contained on a per cpu basis) */ void splz_check(void) { globaldata_t gd = mycpu; thread_t td = gd->gd_curthread; if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && gd->gd_intr_nesting_level == 0 && td->td_nest_count < 2) { splz(); } } /* * This version is integrated into crit_exit, reqflags has already * been tested but td_critcount has not. * * We only want to execute the splz() on the 1->0 transition of * critcount and not in a hard code section or if too deeply nested. */ void lwkt_maybe_splz(thread_t td) { globaldata_t gd = td->td_gd; if (td->td_critcount == 0 && gd->gd_intr_nesting_level == 0 && td->td_nest_count < 2) { splz(); } } /* * This function is used to negotiate a passive release of the current * process/lwp designation with the user scheduler, allowing the user * scheduler to schedule another user thread. The related kernel thread * (curthread) continues running in the released state. */ void lwkt_passive_release(struct thread *td) { struct lwp *lp = td->td_lwp; td->td_release = NULL; lwkt_setpri_self(TDPRI_KERN_USER); lp->lwp_proc->p_usched->release_curproc(lp); } /* * This implements a normal yield. This routine is virtually a nop if * there is nothing to yield to but it will always run any pending interrupts * if called from a critical section. * * This yield is designed for kernel threads without a user context. * * (self contained on a per cpu basis) */ void lwkt_yield(void) { globaldata_t gd = mycpu; thread_t td = gd->gd_curthread; thread_t xtd; if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) splz(); if (td->td_fairq_accum < 0) { lwkt_schedule_self(curthread); lwkt_switch(); } else { xtd = TAILQ_FIRST(&gd->gd_tdrunq); if (xtd && xtd->td_pri > td->td_pri) { lwkt_schedule_self(curthread); lwkt_switch(); } } } /* * This yield is designed for kernel threads with a user context. * * The kernel acting on behalf of the user is potentially cpu-bound, * this function will efficiently allow other threads to run and also * switch to other processes by releasing. * * The lwkt_user_yield() function is designed to have very low overhead * if no yield is determined to be needed. */ void lwkt_user_yield(void) { globaldata_t gd = mycpu; thread_t td = gd->gd_curthread; /* * Always run any pending interrupts in case we are in a critical * section. */ if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) splz(); /* * Switch (which forces a release) if another kernel thread needs * the cpu, if userland wants us to resched, or if our kernel * quantum has run out. */ if (lwkt_resched_wanted() || user_resched_wanted() || td->td_fairq_accum < 0) { lwkt_switch(); } #if 0 /* * Reacquire the current process if we are released. * * XXX not implemented atm. The kernel may be holding locks and such, * so we want the thread to continue to receive cpu. */ if (td->td_release == NULL && lp) { lp->lwp_proc->p_usched->acquire_curproc(lp); td->td_release = lwkt_passive_release; lwkt_setpri_self(TDPRI_USER_NORM); } #endif } /* * Generic schedule. Possibly schedule threads belonging to other cpus and * deal with threads that might be blocked on a wait queue. * * We have a little helper inline function which does additional work after * the thread has been enqueued, including dealing with preemption and * setting need_lwkt_resched() (which prevents the kernel from returning * to userland until it has processed higher priority threads). * * It is possible for this routine to be called after a failed _enqueue * (due to the target thread migrating, sleeping, or otherwise blocked). * We have to check that the thread is actually on the run queue! * * reschedok is an optimized constant propagated from lwkt_schedule() or * lwkt_schedule_noresched(). By default it is non-zero, causing a * reschedule to be requested if the target thread has a higher priority. * The port messaging code will set MSG_NORESCHED and cause reschedok to * be 0, prevented undesired reschedules. */ static __inline void _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount, int reschedok) { thread_t otd; if (ntd->td_flags & TDF_RUNQ) { if (ntd->td_preemptable && reschedok) { ntd->td_preemptable(ntd, ccount); /* YYY +token */ } else if (reschedok) { otd = curthread; if (ntd->td_pri > otd->td_pri) need_lwkt_resched(); } /* * Give the thread a little fair share scheduler bump if it * has been asleep for a while. This is primarily to avoid * a degenerate case for interrupt threads where accumulator * crosses into negative territory unnecessarily. */ if (ntd->td_fairq_lticks != ticks) { ntd->td_fairq_lticks = ticks; ntd->td_fairq_accum += gd->gd_fairq_total_pri; if (ntd->td_fairq_accum > TDFAIRQ_MAX(gd)) ntd->td_fairq_accum = TDFAIRQ_MAX(gd); } } } static __inline void _lwkt_schedule(thread_t td, int reschedok) { globaldata_t mygd = mycpu; KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule(): scheduling gd_idlethread is illegal!")); KKASSERT((td->td_flags & TDF_MIGRATING) == 0); crit_enter_gd(mygd); KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); if (td == mygd->gd_curthread) { _lwkt_enqueue(td); } else { /* * If we own the thread, there is no race (since we are in a * critical section). If we do not own the thread there might * be a race but the target cpu will deal with it. */ #ifdef SMP if (td->td_gd == mygd) { _lwkt_enqueue(td); _lwkt_schedule_post(mygd, td, 1, reschedok); } else { lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0); } #else _lwkt_enqueue(td); _lwkt_schedule_post(mygd, td, 1, reschedok); #endif } crit_exit_gd(mygd); } void lwkt_schedule(thread_t td) { _lwkt_schedule(td, 1); } void lwkt_schedule_noresched(thread_t td) { _lwkt_schedule(td, 0); } #ifdef SMP /* * When scheduled remotely if frame != NULL the IPIQ is being * run via doreti or an interrupt then preemption can be allowed. * * To allow preemption we have to drop the critical section so only * one is present in _lwkt_schedule_post. */ static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame) { thread_t td = curthread; thread_t ntd = arg; if (frame && ntd->td_preemptable) { crit_exit_noyield(td); _lwkt_schedule(ntd, 1); crit_enter_quick(td); } else { _lwkt_schedule(ntd, 1); } } /* * Thread migration using a 'Pull' method. The thread may or may not be * the current thread. It MUST be descheduled and in a stable state. * lwkt_giveaway() must be called on the cpu owning the thread. * * At any point after lwkt_giveaway() is called, the target cpu may * 'pull' the thread by calling lwkt_acquire(). * * We have to make sure the thread is not sitting on a per-cpu tsleep * queue or it will blow up when it moves to another cpu. * * MPSAFE - must be called under very specific conditions. */ void lwkt_giveaway(thread_t td) { globaldata_t gd = mycpu; crit_enter_gd(gd); if (td->td_flags & TDF_TSLEEPQ) tsleep_remove(td); KKASSERT(td->td_gd == gd); TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); td->td_flags |= TDF_MIGRATING; crit_exit_gd(gd); } void lwkt_acquire(thread_t td) { globaldata_t gd; globaldata_t mygd; KKASSERT(td->td_flags & TDF_MIGRATING); gd = td->td_gd; mygd = mycpu; if (gd != mycpu) { cpu_lfence(); KKASSERT((td->td_flags & TDF_RUNQ) == 0); crit_enter_gd(mygd); DEBUG_PUSH_INFO("lwkt_acquire"); while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { #ifdef SMP lwkt_process_ipiq(); #endif cpu_lfence(); } DEBUG_POP_INFO(); cpu_mfence(); td->td_gd = mygd; TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); td->td_flags &= ~TDF_MIGRATING; crit_exit_gd(mygd); } else { crit_enter_gd(mygd); TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); td->td_flags &= ~TDF_MIGRATING; crit_exit_gd(mygd); } } #endif /* * Generic deschedule. Descheduling threads other then your own should be * done only in carefully controlled circumstances. Descheduling is * asynchronous. * * This function may block if the cpu has run out of messages. */ void lwkt_deschedule(thread_t td) { crit_enter(); #ifdef SMP if (td == curthread) { _lwkt_dequeue(td); } else { if (td->td_gd == mycpu) { _lwkt_dequeue(td); } else { lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td); } } #else _lwkt_dequeue(td); #endif crit_exit(); } /* * Set the target thread's priority. This routine does not automatically * switch to a higher priority thread, LWKT threads are not designed for * continuous priority changes. Yield if you want to switch. */ void lwkt_setpri(thread_t td, int pri) { KKASSERT(td->td_gd == mycpu); if (td->td_pri != pri) { KKASSERT(pri >= 0); crit_enter(); if (td->td_flags & TDF_RUNQ) { _lwkt_dequeue(td); td->td_pri = pri; _lwkt_enqueue(td); } else { td->td_pri = pri; } crit_exit(); } } /* * Set the initial priority for a thread prior to it being scheduled for * the first time. The thread MUST NOT be scheduled before or during * this call. The thread may be assigned to a cpu other then the current * cpu. * * Typically used after a thread has been created with TDF_STOPPREQ, * and before the thread is initially scheduled. */ void lwkt_setpri_initial(thread_t td, int pri) { KKASSERT(pri >= 0); KKASSERT((td->td_flags & TDF_RUNQ) == 0); td->td_pri = pri; } void lwkt_setpri_self(int pri) { thread_t td = curthread; KKASSERT(pri >= 0 && pri <= TDPRI_MAX); crit_enter(); if (td->td_flags & TDF_RUNQ) { _lwkt_dequeue(td); td->td_pri = pri; _lwkt_enqueue(td); } else { td->td_pri = pri; } crit_exit(); } /* * 1/hz tick (typically 10ms) x TDFAIRQ_SCALE (typ 8) = 80ms full cycle. * * Example: two competing threads, same priority N. decrement by (2*N) * increment by N*8, each thread will get 4 ticks. */ void lwkt_fairq_schedulerclock(thread_t td) { globaldata_t gd; if (fairq_enable) { while (td) { gd = td->td_gd; if (td != &gd->gd_idlethread) { td->td_fairq_accum -= gd->gd_fairq_total_pri; if (td->td_fairq_accum < -TDFAIRQ_MAX(gd)) td->td_fairq_accum = -TDFAIRQ_MAX(gd); if (td->td_fairq_accum < 0) need_lwkt_resched(); td->td_fairq_lticks = ticks; } td = td->td_preempted; } } } static void lwkt_fairq_accumulate(globaldata_t gd, thread_t td) { td->td_fairq_accum += td->td_pri * TDFAIRQ_SCALE; if (td->td_fairq_accum > TDFAIRQ_MAX(td->td_gd)) td->td_fairq_accum = TDFAIRQ_MAX(td->td_gd); } /* * Migrate the current thread to the specified cpu. * * This is accomplished by descheduling ourselves from the current cpu, * moving our thread to the tdallq of the target cpu, IPI messaging the * target cpu, and switching out. TDF_MIGRATING prevents scheduling * races while the thread is being migrated. * * We must be sure to remove ourselves from the current cpu's tsleepq * before potentially moving to another queue. The thread can be on * a tsleepq due to a left-over tsleep_interlock(). * * We also have to make sure that the switch code doesn't allow an IPI * processing operation to leak in between our send and our switch, or * any other potential livelock such that might occur when we release the * current process designation, so do that first. */ #ifdef SMP static void lwkt_setcpu_remote(void *arg); #endif void lwkt_setcpu_self(globaldata_t rgd) { #ifdef SMP thread_t td = curthread; if (td->td_gd != rgd) { crit_enter_quick(td); if (td->td_release) td->td_release(td); if (td->td_flags & TDF_TSLEEPQ) tsleep_remove(td); td->td_flags |= TDF_MIGRATING; lwkt_deschedule_self(td); TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); lwkt_send_ipiq(rgd, (ipifunc1_t)lwkt_setcpu_remote, td); lwkt_switch(); /* we are now on the target cpu */ TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq); crit_exit_quick(td); } #endif } void lwkt_migratecpu(int cpuid) { #ifdef SMP globaldata_t rgd; rgd = globaldata_find(cpuid); lwkt_setcpu_self(rgd); #endif } /* * Remote IPI for cpu migration (called while in a critical section so we * do not have to enter another one). The thread has already been moved to * our cpu's allq, but we must wait for the thread to be completely switched * out on the originating cpu before we schedule it on ours or the stack * state may be corrupt. We clear TDF_MIGRATING after flushing the GD * change to main memory. * * XXX The use of TDF_MIGRATING might not be sufficient to avoid races * against wakeups. It is best if this interface is used only when there * are no pending events that might try to schedule the thread. */ #ifdef SMP static void lwkt_setcpu_remote(void *arg) { thread_t td = arg; globaldata_t gd = mycpu; int retry = 10000000; DEBUG_PUSH_INFO("lwkt_setcpu_remote"); while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { #ifdef SMP lwkt_process_ipiq(); #endif cpu_lfence(); cpu_pause(); if (--retry == 0) { kprintf("lwkt_setcpu_remote: td->td_flags %08x\n", td->td_flags); retry = 10000000; } } DEBUG_POP_INFO(); td->td_gd = gd; cpu_mfence(); td->td_flags &= ~TDF_MIGRATING; KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); _lwkt_enqueue(td); } #endif struct lwp * lwkt_preempted_proc(void) { thread_t td = curthread; while (td->td_preempted) td = td->td_preempted; return(td->td_lwp); } /* * Create a kernel process/thread/whatever. It shares it's address space * with proc0 - ie: kernel only. * * NOTE! By default new threads are created with the MP lock held. A * thread which does not require the MP lock should release it by calling * rel_mplock() at the start of the new thread. */ int lwkt_create(void (*func)(void *), void *arg, struct thread **tdp, thread_t template, int tdflags, int cpu, const char *fmt, ...) { thread_t td; __va_list ap; td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu, tdflags); if (tdp) *tdp = td; cpu_set_thread_handler(td, lwkt_exit, func, arg); /* * Set up arg0 for 'ps' etc */ __va_start(ap, fmt); kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap); __va_end(ap); /* * Schedule the thread to run */ if ((td->td_flags & TDF_STOPREQ) == 0) lwkt_schedule(td); else td->td_flags &= ~TDF_STOPREQ; return 0; } /* * Destroy an LWKT thread. Warning! This function is not called when * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and * uses a different reaping mechanism. */ void lwkt_exit(void) { thread_t td = curthread; thread_t std; globaldata_t gd; /* * Do any cleanup that might block here */ if (td->td_flags & TDF_VERBOSE) kprintf("kthread %p %s has exited\n", td, td->td_comm); caps_exit(td); biosched_done(td); dsched_exit_thread(td); /* * Get us into a critical section to interlock gd_freetd and loop * until we can get it freed. * * We have to cache the current td in gd_freetd because objcache_put()ing * it would rip it out from under us while our thread is still active. */ gd = mycpu; crit_enter_quick(td); while ((std = gd->gd_freetd) != NULL) { KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0); gd->gd_freetd = NULL; objcache_put(thread_cache, std); } /* * Remove thread resources from kernel lists and deschedule us for * the last time. We cannot block after this point or we may end * up with a stale td on the tsleepq. */ if (td->td_flags & TDF_TSLEEPQ) tsleep_remove(td); lwkt_deschedule_self(td); lwkt_remove_tdallq(td); KKASSERT(td->td_refs == 0); /* * Final cleanup */ KKASSERT(gd->gd_freetd == NULL); if (td->td_flags & TDF_ALLOCATED_THREAD) gd->gd_freetd = td; cpu_thread_exit(); } void lwkt_remove_tdallq(thread_t td) { KKASSERT(td->td_gd == mycpu); TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); } /* * Code reduction and branch prediction improvements. Call/return * overhead on modern cpus often degenerates into 0 cycles due to * the cpu's branch prediction hardware and return pc cache. We * can take advantage of this by not inlining medium-complexity * functions and we can also reduce the branch prediction impact * by collapsing perfectly predictable branches into a single * procedure instead of duplicating it. * * Is any of this noticeable? Probably not, so I'll take the * smaller code size. */ void crit_exit_wrapper(__DEBUG_CRIT_ARG__) { _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__); } void crit_panic(void) { thread_t td = curthread; int lcrit = td->td_critcount; td->td_critcount = 0; panic("td_critcount is/would-go negative! %p %d", td, lcrit); /* NOT REACHED */ } #ifdef SMP /* * Called from debugger/panic on cpus which have been stopped. We must still * process the IPIQ while stopped, even if we were stopped while in a critical * section (XXX). * * If we are dumping also try to process any pending interrupts. This may * or may not work depending on the state of the cpu at the point it was * stopped. */ void lwkt_smp_stopped(void) { globaldata_t gd = mycpu; crit_enter_gd(gd); if (dumping) { lwkt_process_ipiq(); splz(); } else { lwkt_process_ipiq(); } crit_exit_gd(gd); } #endif