/* * Copyright (c) 2003-2011 The DragonFly Project. All rights reserved. * * This code is derived from software contributed to The DragonFly Project * by Matthew Dillon <dillon@backplane.com> * * 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 <sys/param.h> #include <sys/systm.h> #include <sys/kernel.h> #include <sys/proc.h> #include <sys/rtprio.h> #include <sys/kinfo.h> #include <sys/malloc.h> #include <sys/queue.h> #include <sys/sysctl.h> #include <sys/kthread.h> #include <machine/cpu.h> #include <sys/lock.h> #include <sys/spinlock.h> #include <sys/ktr.h> #include <sys/indefinite.h> #include <sys/thread2.h> #include <sys/spinlock2.h> #include <sys/indefinite2.h> #include <sys/dsched.h> #include <vm/vm.h> #include <vm/vm_param.h> #include <vm/vm_kern.h> #include <vm/vm_object.h> #include <vm/vm_page.h> #include <vm/vm_map.h> #include <vm/vm_pager.h> #include <vm/vm_extern.h> #include <machine/stdarg.h> #include <machine/smp.h> #include <machine/clock.h> #define LOOPMASK #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", int cpu, struct thread *td); KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", int cpu, struct thread *td); KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", struct thread *td, char *comm); KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", struct thread *td); static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads"); MALLOC_DEFINE(M_FPUCTX, "fpuctx", "kernel FPU contexts"); #ifdef INVARIANTS static int panic_on_cscount = 0; #endif #ifdef DEBUG_LWKT_THREAD static int64_t switch_count = 0; static int64_t preempt_hit = 0; static int64_t preempt_miss = 0; static int64_t preempt_weird = 0; #endif static int lwkt_use_spin_port; __read_mostly static struct objcache *thread_cache; int cpu_mwait_spin = 0; static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame); static void lwkt_setcpu_remote(void *arg); /* * 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 #ifdef DEBUG_LWKT_THREAD 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."); #endif extern int lwkt_sched_debug; int lwkt_sched_debug = 0; SYSCTL_INT(_lwkt, OID_AUTO, sched_debug, CTLFLAG_RW, &lwkt_sched_debug, 0, "Scheduler debug"); __read_mostly static u_int lwkt_spin_loops = 10; SYSCTL_UINT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW, &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon"); __read_mostly static int preempt_enable = 1; SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW, &preempt_enable, 0, "Enable preemption"); static int lwkt_cache_threads = 0; SYSCTL_INT(_lwkt, OID_AUTO, cache_threads, CTLFLAG_RD, &lwkt_cache_threads, 0, "thread+kstack cache"); /* * 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_tdrunqcount; if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL) atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING); } } /* * Priority enqueue. * * There are a limited number of lwkt threads runnable since user * processes only schedule one at a time per cpu. However, there can * be many user processes in kernel mode exiting from a tsleep() which * become runnable. * * We scan the queue in both directions to help deal with degenerate * situations when hundreds or thousands (or more) threads are runnable. * * NOTE: lwkt_schedulerclock() will force a round-robin based on td_pri and * will ignore user priority. This is to ensure that user threads in * kernel mode get cpu at some point regardless of what the user * scheduler thinks. */ static __inline void _lwkt_enqueue(thread_t td) { thread_t xtd; /* forward scan */ thread_t rtd; /* reverse scan */ 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 { /* * NOTE: td_upri - higher numbers more desireable, same sense * as td_pri (typically reversed from lwp_upri). * * In the equal priority case we want the best selection * at the beginning so the less desireable selections know * that they have to setrunqueue/go-to-another-cpu, even * though it means switching back to the 'best' selection. * This also avoids degenerate situations when many threads * are runnable or waking up at the same time. * * If upri matches exactly place at end/round-robin. */ rtd = TAILQ_LAST(&gd->gd_tdrunq, lwkt_queue); while (xtd && (xtd->td_pri > td->td_pri || (xtd->td_pri == td->td_pri && xtd->td_upri >= td->td_upri))) { xtd = TAILQ_NEXT(xtd, td_threadq); /* * Doing a reverse scan at the same time is an optimization * for the insert-closer-to-tail case that avoids having to * scan the entire list. This situation can occur when * thousands of threads are woken up at the same time. */ if (rtd->td_pri > td->td_pri || (rtd->td_pri == td->td_pri && rtd->td_upri >= td->td_upri)) { TAILQ_INSERT_AFTER(&gd->gd_tdrunq, rtd, td, td_threadq); goto skip; } rtd = TAILQ_PREV(rtd, lwkt_queue, td_threadq); } if (xtd) TAILQ_INSERT_BEFORE(xtd, td, td_threadq); else TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); } skip: ++gd->gd_tdrunqcount; /* * Request a LWKT reschedule if we are now at the head of the queue. */ if (TAILQ_FIRST(&gd->gd_tdrunq) == td) need_lwkt_resched(); } } 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; td->td_mpflags = 0; 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); td->td_kstack = NULL; td->td_flags = 0; } /* * Initialize the lwkt s/system. * * Nominally cache up to 32 thread + kstack structures. Cache more on * systems with a lot of cpu cores. */ static void lwkt_init(void) { TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads); if (lwkt_cache_threads == 0) { lwkt_cache_threads = ncpus * 4; if (lwkt_cache_threads < 32) lwkt_cache_threads = 32; } thread_cache = objcache_create_mbacked( M_THREAD, sizeof(struct thread), 0, lwkt_cache_threads, _lwkt_thread_ctor, _lwkt_thread_dtor, NULL); } SYSINIT(lwkt_init, SI_BOOT2_LWKT_INIT, SI_ORDER_FIRST, lwkt_init, 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_mpflags & LWP_MP_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); lockinit(&gd->gd_sysctllock, "sysctl", 0, LK_CANRECURSE); } /* * 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) { static int cpu_rotator; 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_PREEMPT_LOCK)) == 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) { if (cpu < 0) { stack = (void *)kmem_alloc_stack(kernel_map, stksize, 0); } else { stack = (void *)kmem_alloc_stack(kernel_map, stksize, KM_CPU(cpu)); } flags |= TDF_ALLOCATED_STACK; } if (cpu < 0) { cpu = ++cpu_rotator; cpu_ccfence(); cpu = (uint32_t)cpu % (uint32_t)ncpus; } 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. */ 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); } /* * 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_mpflags = 0; td->td_type = TD_TYPE_GENERIC; td->td_gd = gd; td->td_pri = TDPRI_KERN_DAEMON; td->td_critcount = 1; td->td_toks_have = NULL; td->td_toks_stop = &td->td_toks_base; if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT)) { lwkt_initport_spin(&td->td_msgport, td, (flags & TDF_FIXEDCPU) ? TRUE : FALSE); } else { lwkt_initport_thread(&td->td_msgport, td); } pmap_init_thread(td); /* * 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); } dsched_enter_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); } /* * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE * this does not prevent the thread from migrating to another cpu so the * gd_tdallq state is not protected by this. */ 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_free_thread(thread_t td) { KKASSERT(td->td_refs == 0); KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK | TDF_RUNQ | TDF_TSLEEPQ | TDF_KERNELFP)) == 0); if (td->td_kfpuctx) { kfree(td->td_kfpuctx, M_FPUCTX); td->td_kfpuctx = NULL; } 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 upri; #ifdef LOOPMASK uint64_t tsc_base = rdtsc(); #endif KKASSERT(gd->gd_processing_ipiq == 0); KKASSERT(td->td_flags & TDF_RUNNING); /* * 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 " "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; } } /* * Release our current user process designation if we are blocking * or if a user reschedule was requested. * * NOTE: This function is NOT called if we are switching into or * returning from a preemption. * * NOTE: Releasing our current user process designation may cause * it to be assigned to another thread, which in turn will * cause us to block in the usched acquire code when we attempt * to return to userland. * * NOTE: On SMP systems this can be very nasty when heavy token * contention is present so we want to be careful not to * release the designation gratuitously. */ if (td->td_release && (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) { td->td_release(td); } /* * Release all tokens. Once we do this we must remain in the critical * section and cannot run IPIs or other interrupts until we switch away * because they may implode if they try to get a token using our thread * context. */ 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 == 0 || panicstr != NULL, ("lwkt_switch: still holding %d exclusive spinlocks!", gd->gd_spinlocks)); #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 /* * 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; ntd->td_contended = 0; /* reset contended */ /* * 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. * * NOTE: The interrupt may not have descheduled ntd. * * NOTE: We do not reschedule if there are no threads on the runq. * (ntd could be the idlethread). */ xtd = TAILQ_FIRST(&gd->gd_tdrunq); if (xtd && xtd != ntd) need_lwkt_resched(); goto havethread_preempted; } /* * Figure out switch target. If we cannot switch to our desired target * look for a thread that we can switch to. * * NOTE! The limited spin loop and related parameters are extremely * important for system performance, particularly for pipes and * concurrent conflicting VM faults. */ clear_lwkt_resched(); ntd = TAILQ_FIRST(&gd->gd_tdrunq); if (ntd) { do { if (TD_TOKS_NOT_HELD(ntd) || lwkt_getalltokens(ntd, (ntd->td_contended > lwkt_spin_loops))) { goto havethread; } ++ntd->td_contended; /* overflow ok */ if (gd->gd_indefinite.type == 0) indefinite_init(&gd->gd_indefinite, NULL, NULL, 0, 't'); #ifdef LOOPMASK if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) { kprintf("lwkt_switch: WARNING, excessive token contention " "cpu %d, %d sec, " "td %p (%s)\n", gd->gd_cpuid, ntd->td_contended, ntd, ntd->td_comm); tsc_base = rdtsc(); } #endif } while (ntd->td_contended < (lwkt_spin_loops >> 1)); upri = ntd->td_upri; /* * Bleh, the thread we wanted to switch to has a contended token. * See if we can switch to another thread. * * We generally don't want to do this because it represents a * priority inversion, but contending tokens on the same cpu can * cause real problems if we don't now that we have an exclusive * priority mechanism over shared for tokens. * * The solution is to allow threads with pending tokens to compete * for them (a lower priority thread will get less cpu once it * returns from the kernel anyway). If a thread does not have * any contending tokens, we go by td_pri and upri. */ while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) { if (TD_TOKS_NOT_HELD(ntd) && ntd->td_pri < TDPRI_KERN_LPSCHED && upri > ntd->td_upri) { continue; } if (upri < ntd->td_upri) upri = ntd->td_upri; /* * Try this one. */ if (TD_TOKS_NOT_HELD(ntd) || lwkt_getalltokens(ntd, (ntd->td_contended > lwkt_spin_loops))) { goto havethread; } ++ntd->td_contended; /* overflow ok */ } /* * Fall through, switch to idle thread to get us out of the current * context. Since we were contended, prevent HLT by flagging a * LWKT reschedule. */ need_lwkt_resched(); } /* * We either contended on ntd or the runq is empty. We must switch * through the idle thread to get out of the current context. */ ntd = &gd->gd_idlethread; if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) ASSERT_NO_TOKENS_HELD(ntd); cpu_time.cp_msg[0] = 0; goto haveidle; havethread: /* * Clear gd_idle_repeat when doing a normal switch to a non-idle * thread. */ ntd->td_wmesg = NULL; ntd->td_contended = 0; /* reset once scheduled */ ++gd->gd_cnt.v_swtch; gd->gd_idle_repeat = 0; /* * If we were busy waiting record final disposition */ if (gd->gd_indefinite.type) indefinite_done(&gd->gd_indefinite); 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) { /* * Execute the actual thread switch operation. This function * returns to the current thread and returns the previous thread * (which may be different from the thread we switched to). * * We are responsible for marking ntd as TDF_RUNNING. */ KKASSERT((ntd->td_flags & TDF_RUNNING) == 0); #ifdef DEBUG_LWKT_THREAD ++switch_count; #endif KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd); ntd->td_flags |= TDF_RUNNING; lwkt_switch_return(td->td_switch(ntd)); /* ntd invalid, td_switch() can return a different thread_t */ } /* * catch-all. XXX is this strictly needed? */ splz_check(); /* NOTE: current cpu may have changed after switch */ crit_exit_quick(td); } /* * Called by assembly in the td_switch (thread restore path) for thread * bootstrap cases which do not 'return' to lwkt_switch(). */ void lwkt_switch_return(thread_t otd) { globaldata_t rgd; #ifdef LOOPMASK uint64_t tsc_base = rdtsc(); #endif int exiting; exiting = otd->td_flags & TDF_EXITING; cpu_ccfence(); /* * Check if otd was migrating. Now that we are on ntd we can finish * up the migration. This is a bit messy but it is the only place * where td is known to be fully descheduled. * * We can only activate the migration if otd was migrating but not * held on the cpu due to a preemption chain. We still have to * clear TDF_RUNNING on the old thread either way. * * We are responsible for clearing the previously running thread's * TDF_RUNNING. */ if ((rgd = otd->td_migrate_gd) != NULL && (otd->td_flags & TDF_PREEMPT_LOCK) == 0) { KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) == (TDF_MIGRATING | TDF_RUNNING)); otd->td_migrate_gd = NULL; otd->td_flags &= ~TDF_RUNNING; lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd); } else { otd->td_flags &= ~TDF_RUNNING; } /* * Final exit validations (see lwp_wait()). Note that otd becomes * invalid the *instant* we set TDF_MP_EXITSIG. * * Use the EXITING status loaded from before we clear TDF_RUNNING, * because if it is not set otd becomes invalid the instant we clear * TDF_RUNNING on it (otherwise, if the system is fast enough, we * might 'steal' TDF_EXITING from another switch-return!). */ while (exiting) { u_int mpflags; mpflags = otd->td_mpflags; cpu_ccfence(); if (mpflags & TDF_MP_EXITWAIT) { if (atomic_cmpset_int(&otd->td_mpflags, mpflags, mpflags | TDF_MP_EXITSIG)) { wakeup(otd); break; } } else { if (atomic_cmpset_int(&otd->td_mpflags, mpflags, mpflags | TDF_MP_EXITSIG)) { wakeup(otd); break; } } #ifdef LOOPMASK if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) { kprintf("lwkt_switch_return: excessive TDF_EXITING " "thread %p\n", otd); tsc_base = rdtsc(); } #endif } } /* * Request that the target thread preempt the current thread. Preemption * can only occur only: * * - If our critical section is the one that we were called with * - The relative priority of the target thread is higher * - The target is not excessively interrupt-nested via td_nest_count * - The target thread holds no tokens. * - The target thread is not already scheduled and belongs to the * current cpu. * - The current thread is not holding any spin-locks. * * 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). * * Preemption is typically limited to interrupt threads. * * Operation works in a fairly straight-forward manner. The normal * scheduling code is bypassed and we switch directly to the target * thread. When the target thread attempts to block or switch away * code at the base of lwkt_switch() will switch directly back to our * thread. Our thread is able to retain whatever tokens it holds and * if the target needs one of them the target will switch back to us * and reschedule itself normally. */ void lwkt_preempt(thread_t ntd, int critcount) { struct globaldata *gd = mycpu; thread_t xtd; 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). */ KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri)); td = gd->gd_curthread; if (preempt_enable == 0) { #ifdef DEBUG_LWKT_THREAD ++preempt_miss; #endif return; } if (ntd->td_pri <= td->td_pri) { #ifdef DEBUG_LWKT_THREAD ++preempt_miss; #endif return; } if (td->td_critcount > critcount) { #ifdef DEBUG_LWKT_THREAD ++preempt_miss; #endif return; } if (td->td_nest_count >= 2) { #ifdef DEBUG_LWKT_THREAD ++preempt_miss; #endif return; } if (td->td_cscount) { #ifdef DEBUG_LWKT_THREAD ++preempt_miss; #endif return; } if (ntd->td_gd != gd) { #ifdef DEBUG_LWKT_THREAD ++preempt_miss; #endif return; } /* * 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 == 0); if (TD_TOKS_HELD(ntd)) { #ifdef DEBUG_LWKT_THREAD ++preempt_miss; #endif return; } if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) { #ifdef DEBUG_LWKT_THREAD ++preempt_weird; #endif return; } if (ntd->td_preempted) { #ifdef DEBUG_LWKT_THREAD ++preempt_hit; #endif return; } KKASSERT(gd->gd_processing_ipiq == 0); /* * 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. * * A preemption must switch back to the original thread, assert the * case. */ #ifdef DEBUG_LWKT_THREAD ++preempt_hit; #endif 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; KKASSERT((ntd->td_flags & TDF_RUNNING) == 0); ntd->td_flags |= TDF_RUNNING; xtd = td->td_switch(ntd); KKASSERT(xtd == ntd); lwkt_switch_return(xtd); 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. * * NOTE: gd->gd_spinlocks is implied to be 0 when td_critcount is 0. */ 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(); } } /* * Drivers which set up processing co-threads can call this function to * run the co-thread at a higher priority and to allow it to preempt * normal threads. */ void lwkt_set_interrupt_support_thread(void) { thread_t td = curthread; lwkt_setpri_self(TDPRI_INT_SUPPORT); td->td_flags |= TDF_INTTHREAD; td->td_preemptable = lwkt_preempt; } /* * 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 LWKT yield, allowing a kernel thread to yield to other * kernel threads at the same or higher priority. This function can be * called in a tight loop and will typically only yield once per tick. * * Most kernel threads run at the same priority in order to allow equal * sharing. * * (self contained on a per cpu basis) */ void lwkt_yield(void) { globaldata_t gd = mycpu; thread_t td = gd->gd_curthread; /* * Should never be called with spinlocks held but there is a path * via ACPI where it might happen. */ if (gd->gd_spinlocks) return; /* * Safe to call splz if we are not too-heavily nested. */ if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) splz(); /* * Caller allows switching */ if (lwkt_resched_wanted()) { atomic_set_int(&td->td_mpflags, TDF_MP_DIDYIELD); lwkt_schedule_self(td); lwkt_switch(); } } /* * The quick version processes pending interrupts and higher-priority * LWKT threads but will not round-robin same-priority LWKT threads. * * When called while attempting to return to userland the only same-pri * threads are the ones which have already tried to become the current * user process. */ void lwkt_yield_quick(void) { globaldata_t gd = mycpu; thread_t td = gd->gd_curthread; if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) splz(); if (lwkt_resched_wanted()) { crit_enter(); if (TAILQ_FIRST(&gd->gd_tdrunq) == td) { clear_lwkt_resched(); } else { atomic_set_int(&td->td_mpflags, TDF_MP_DIDYIELD); lwkt_schedule_self(curthread); lwkt_switch(); } crit_exit(); } } /* * 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; /* * Should never be called with spinlocks held but there is a path * via ACPI where it might happen. */ if (gd->gd_spinlocks) return; /* * 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()) { 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! */ static __inline void _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount) { if (ntd->td_flags & TDF_RUNQ) { if (ntd->td_preemptable) { ntd->td_preemptable(ntd, ccount); /* YYY +token */ } } } static __inline void _lwkt_schedule(thread_t td) { 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_mpflags & LWP_MP_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. */ if (td->td_gd == mygd) { _lwkt_enqueue(td); _lwkt_schedule_post(mygd, td, 1); } else { lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0); } } crit_exit_gd(mygd); } void lwkt_schedule(thread_t td) { _lwkt_schedule(td); } void lwkt_schedule_noresched(thread_t td) /* XXX not impl */ { _lwkt_schedule(td); } /* * 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); crit_enter_quick(td); } else { _lwkt_schedule(ntd); } } /* * 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) { #ifdef LOOPMASK uint64_t tsc_base = rdtsc(); #endif 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)) { lwkt_process_ipiq(); cpu_lfence(); #ifdef _KERNEL_VIRTUAL vkernel_yield(); #endif #ifdef LOOPMASK if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) { kprintf("lwkt_acquire: stuck td %p td->td_flags %08x\n", td, td->td_flags); tsc_base = rdtsc(); } #endif } 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); } } /* * 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(); 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); } } 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) { if (td->td_pri != pri) { KKASSERT(pri >= 0); crit_enter(); if (td->td_flags & TDF_RUNQ) { KKASSERT(td->td_gd == mycpu); _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(); } /* * hz tick scheduler clock for LWKT threads */ void lwkt_schedulerclock(thread_t td) { globaldata_t gd = td->td_gd; thread_t xtd; xtd = TAILQ_FIRST(&gd->gd_tdrunq); if (xtd == td) { /* * If the current thread is at the head of the runq shift it to the * end of any equal-priority threads and request a LWKT reschedule * if it moved. * * Ignore upri in this situation. There will only be one user thread * in user mode, all others will be user threads running in kernel * mode and we have to make sure they get some cpu. */ xtd = TAILQ_NEXT(td, td_threadq); if (xtd && xtd->td_pri == td->td_pri) { TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq); 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); need_lwkt_resched(); } } else if (xtd) { /* * If we scheduled a thread other than the one at the head of the * queue always request a reschedule every tick. */ need_lwkt_resched(); } /* else curthread probably the idle thread, no need to reschedule */ } /* * Migrate the current thread to the specified cpu. * * This is accomplished by descheduling ourselves from the current cpu * and setting td_migrate_gd. The lwkt_switch() code will detect that the * 'old' thread wants to migrate after it has been completely switched out * and will complete the migration. * * TDF_MIGRATING prevents scheduling races while the thread is being migrated. * * We must be sure to release our current process designation (if a user * process) before clearing out any tsleepq we are on because the release * code may re-add us. * * 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(). */ void lwkt_setcpu_self(globaldata_t rgd) { 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); /* * Set TDF_MIGRATING to prevent a spurious reschedule while we are * trying to deschedule ourselves and switch away, then deschedule * ourself, remove us from tdallq, and set td_migrate_gd. Finally, * call lwkt_switch() to complete the operation. */ td->td_flags |= TDF_MIGRATING; lwkt_deschedule_self(td); TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); td->td_migrate_gd = rgd; lwkt_switch(); /* * We are now on the target cpu */ KKASSERT(rgd == mycpu); TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq); crit_exit_quick(td); } } void lwkt_migratecpu(int cpuid) { globaldata_t rgd; rgd = globaldata_find(cpuid); lwkt_setcpu_self(rgd); } /* * Remote IPI for cpu migration (called while in a critical section so we * do not have to enter another one). * * The thread (td) has already been completely descheduled from the * originating cpu and we can simply assert the case. The thread is * assigned to the new cpu and enqueued. * * The thread will re-add itself to tdallq when it resumes execution. */ static void lwkt_setcpu_remote(void *arg) { thread_t td = arg; globaldata_t gd = mycpu; KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0); td->td_gd = gd; cpu_mfence(); td->td_flags &= ~TDF_MIGRATING; KKASSERT(td->td_migrate_gd == NULL); KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0); _lwkt_enqueue(td); } 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. * * If the cpu is not specified one will be selected. In the future * specifying a cpu of -1 will enable kernel thread migration between * cpus. */ 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_NOSTART) td->td_flags &= ~TDF_NOSTART; else lwkt_schedule(td); 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 */ 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. * * We are the current thread so of course our own TDF_RUNNING bit will * be set, so unlike the lwp reap code we don't wait for it to clear. */ gd = mycpu; crit_enter_quick(td); for (;;) { if (td->td_refs) { tsleep(td, 0, "tdreap", 1); continue; } if ((std = gd->gd_freetd) != NULL) { KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0); gd->gd_freetd = NULL; objcache_put(thread_cache, std); continue; } break; } /* * 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. * * None of this may block, the critical section is the only thing * protecting tdallq and the only thing preventing new lwkt_hold() * thread refs now. */ 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; cpu_ccfence(); panic("td_critcount is/would-go negative! %p %d", td, lcrit); /* NOT REACHED */ } /* * Called from debugger/panic on cpus which have been stopped. We must still * process the IPIQ while stopped. * * 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; if (dumping) { lwkt_process_ipiq(); --gd->gd_intr_nesting_level; splz(); ++gd->gd_intr_nesting_level; } else { lwkt_process_ipiq(); } cpu_smp_stopped(); }
