/* * Copyright (c) 2003,2004 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. * * $DragonFly: src/sys/kern/lwkt_thread.c,v 1.120 2008/10/26 04:29:19 sephe Exp $ */ /* * 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 "opt_ddb.h" #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 #ifdef DDB #include #endif static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads"); static int untimely_switch = 0; #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 = 0; static __int64_t mplock_contention_count = 0; static int lwkt_use_spin_port; static struct objcache *thread_cache; /* * 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); SYSCTL_INT(_lwkt, OID_AUTO, untimely_switch, CTLFLAG_RW, &untimely_switch, 0, ""); #ifdef INVARIANTS SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0, ""); #endif SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0, ""); SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0, ""); SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0, ""); SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0, ""); #ifdef INVARIANTS SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count, CTLFLAG_RW, &token_contention_count, 0, "spinning due to token contention"); SYSCTL_QUAD(_lwkt, OID_AUTO, mplock_contention_count, CTLFLAG_RW, &mplock_contention_count, 0, "spinning due to MPLOCK contention"); #endif /* * Kernel Trace */ #if !defined(KTR_GIANT_CONTENTION) #define KTR_GIANT_CONTENTION KTR_ALL #endif KTR_INFO_MASTER(giant); KTR_INFO(KTR_GIANT_CONTENTION, giant, beg, 0, "thread=%p", sizeof(void *)); KTR_INFO(KTR_GIANT_CONTENTION, giant, end, 1, "thread=%p", sizeof(void *)); #define loggiant(name) KTR_LOG(giant_ ## name, curthread) /* * 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) { int nq = td->td_pri & TDPRI_MASK; struct globaldata *gd = td->td_gd; td->td_flags &= ~TDF_RUNQ; TAILQ_REMOVE(&gd->gd_tdrunq[nq], td, td_threadq); /* runqmask is passively cleaned up by the switcher */ } } static __inline void _lwkt_enqueue(thread_t td) { if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_TSLEEPQ|TDF_BLOCKQ)) == 0) { int nq = td->td_pri & TDPRI_MASK; struct globaldata *gd = td->td_gd; td->td_flags |= TDF_RUNQ; TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], td, td_threadq); gd->gd_runqmask |= 1 << nq; } } 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) { 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) { int i; for (i = 0; i < sizeof(gd->gd_tdrunq)/sizeof(gd->gd_tdrunq[0]); ++i) TAILQ_INIT(&gd->gd_tdrunq[i]); gd->gd_runqmask = 0; 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) { if ((td = gd->gd_freetd) != NULL) gd->gd_freetd = NULL; else td = objcache_get(thread_cache, M_WAITOK); 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(&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 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 + TDPRI_CRIT; #ifdef SMP if ((flags & TDF_MPSAFE) == 0) td->td_mpcount = 1; #endif 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 } 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); } void lwkt_hold(thread_t td) { ++td->td_refs; } void lwkt_rele(thread_t td) { KKASSERT(td->td_refs > 0); --td->td_refs; } void lwkt_wait_free(thread_t td) { while (td->td_refs) tsleep(td, 0, "tdreap", hz); } void lwkt_free_thread(thread_t td) { KASSERT((td->td_flags & TDF_RUNNING) == 0, ("lwkt_free_thread: did not exit! %p", td)); 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; } } /* * 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. * * The MP lock may be out of sync with the thread's td_mpcount. lwkt_switch() * cleans it up. Note that the td_switch() function cannot do anything that * requires the MP lock since the MP lock will have already been setup for * the target thread (not the current thread). It's nice to have a scheduler * that does not need the MP lock to work because it allows us to do some * really cool high-performance MP lock optimizations. * * 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). */ void lwkt_switch(void) { globaldata_t gd = mycpu; thread_t td = gd->gd_curthread; thread_t ntd; #ifdef SMP int mpheld; #endif /* * 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 && panicstr == NULL) { panic("lwkt_switch: cannot switch from within " "a fast interrupt, yet, 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 or IPI, " "thread %p (%s)\n", td, td->td_comm); #ifdef DDB db_print_backtrace(); #endif } 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->td_toks) lwkt_relalltokens(td); /* * We had better not be holding any spin locks, but don't get into an * endless panic loop. */ KASSERT(gd->gd_spinlock_rd == NULL || panicstr != NULL, ("lwkt_switch: still holding a shared spinlock %p!", gd->gd_spinlock_rd)); KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL, ("lwkt_switch: still holding %d exclusive spinlocks!", gd->gd_spinlocks_wr)); #ifdef SMP /* * td_mpcount cannot be used to determine if we currently hold the * MP lock because get_mplock() will increment it prior to attempting * to get the lock, and switch out if it can't. Our ownership of * the actual lock will remain stable while we are in a critical section * (but, of course, another cpu may own or release the lock so the * actual value of mp_lock is not stable). */ mpheld = MP_LOCK_HELD(); #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 ((ntd = td->td_preempted) != NULL) { /* * 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. */ KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK); #ifdef SMP if (ntd->td_mpcount && mpheld == 0) { panic("MPLOCK NOT HELD ON RETURN: %p %p %d %d", td, ntd, td->td_mpcount, ntd->td_mpcount); } if (ntd->td_mpcount) { td->td_mpcount -= ntd->td_mpcount; KKASSERT(td->td_mpcount >= 0); } #endif ntd->td_flags |= TDF_PREEMPT_DONE; /* * XXX. 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 (gd->gd_runqmask > (2 << (ntd->td_pri & TDPRI_MASK)) - 1) need_lwkt_resched(); /* YYY release mp lock on switchback if original doesn't need it */ } else { /* * Priority queue / round-robin at each priority. Note that user * processes run at a fixed, low priority and the user process * scheduler deals with interactions between user processes * by scheduling and descheduling them from the LWKT queue as * necessary. * * We have to adjust the MP lock for the target thread. If we * need the MP lock and cannot obtain it we try to locate a * thread that does not need the MP lock. If we cannot, we spin * instead of HLT. * * A similar issue exists for the tokens held by the target thread. * If we cannot obtain ownership of the tokens we cannot immediately * schedule the thread. */ /* * If an LWKT reschedule was requested, well that is what we are * doing now so clear it. */ clear_lwkt_resched(); again: if (gd->gd_runqmask) { int nq = bsrl(gd->gd_runqmask); if ((ntd = TAILQ_FIRST(&gd->gd_tdrunq[nq])) == NULL) { gd->gd_runqmask &= ~(1 << nq); goto again; } #ifdef SMP /* * THREAD SELECTION FOR AN SMP MACHINE BUILD * * If the target needs the MP lock and we couldn't get it, * or if the target is holding tokens and we could not * gain ownership of the tokens, continue looking for a * thread to schedule and spin instead of HLT if we can't. * * NOTE: the mpheld variable invalid after this conditional, it * can change due to both cpu_try_mplock() returning success * AND interactions in lwkt_getalltokens() due to the fact that * we are trying to check the mpcount of a thread other then * the current thread. Because of this, if the current thread * is not holding td_mpcount, an IPI indirectly run via * lwkt_getalltokens() can obtain and release the MP lock and * cause the core MP lock to be released. */ if ((ntd->td_mpcount && mpheld == 0 && !cpu_try_mplock()) || (ntd->td_toks && lwkt_getalltokens(ntd) == 0) ) { u_int32_t rqmask = gd->gd_runqmask; mpheld = MP_LOCK_HELD(); ntd = NULL; while (rqmask) { TAILQ_FOREACH(ntd, &gd->gd_tdrunq[nq], td_threadq) { if (ntd->td_mpcount && !mpheld && !cpu_try_mplock()) { /* spinning due to MP lock being held */ #ifdef INVARIANTS ++mplock_contention_count; #endif /* mplock still not held, 'mpheld' still valid */ continue; } /* * mpheld state invalid after getalltokens call returns * failure, but the variable is only needed for * the loop. */ if (ntd->td_toks && !lwkt_getalltokens(ntd)) { /* spinning due to token contention */ #ifdef INVARIANTS ++token_contention_count; #endif mpheld = MP_LOCK_HELD(); continue; } break; } if (ntd) break; rqmask &= ~(1 << nq); nq = bsrl(rqmask); } if (ntd == NULL) { cpu_mplock_contested(); ntd = &gd->gd_idlethread; ntd->td_flags |= TDF_IDLE_NOHLT; goto using_idle_thread; } else { ++gd->gd_cnt.v_swtch; TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); } } else { ++gd->gd_cnt.v_swtch; TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); } #else /* * THREAD SELECTION FOR A UP MACHINE BUILD. We don't have to * worry about tokens or the BGL. However, we still have * to call lwkt_getalltokens() in order to properly detect * stale tokens. This call cannot fail for a UP build! */ lwkt_getalltokens(ntd); ++gd->gd_cnt.v_swtch; TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); #endif } else { /* * We have nothing to run but only let the idle loop halt * the cpu if there are no pending interrupts. */ ntd = &gd->gd_idlethread; if (gd->gd_reqflags & RQF_IDLECHECK_MASK) ntd->td_flags |= TDF_IDLE_NOHLT; #ifdef SMP using_idle_thread: /* * The idle thread should not be holding the MP lock unless we * are trapping in the kernel or in a panic. Since we select the * idle thread unconditionally when no other thread is available, * if the MP lock is desired during a panic or kernel trap, we * have to loop in the scheduler until we get it. */ if (ntd->td_mpcount) { mpheld = MP_LOCK_HELD(); if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) { panic("Idle thread %p was holding the BGL!", ntd); } else if (mpheld == 0) { cpu_mplock_contested(); goto again; } } #endif } } KASSERT(ntd->td_pri >= TDPRI_CRIT, ("priority problem in lwkt_switch %d %d", td->td_pri, ntd->td_pri)); /* * Do the actual switch. 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. */ #ifdef SMP if (ntd->td_mpcount == 0 ) { if (MP_LOCK_HELD()) cpu_rel_mplock(); } else { ASSERT_MP_LOCK_HELD(ntd); } #endif if (td != ntd) { ++switch_count; 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. * critpri 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). * * The target thread inherits our MP count (added to its own) for the * duration of the preemption in order to preserve the atomicy of the * MP lock during the preemption. Therefore, any preempting targets must be * careful in regards to MP assertions. Note that the MP count may be * out of sync with the physical mp_lock, but we do not have to preserve * the original ownership of the lock if it was out of synch (that is, we * can leave it synchronized on return). */ void lwkt_preempt(thread_t ntd, int critpri) { struct globaldata *gd = mycpu; thread_t td; #ifdef SMP int mpheld; int savecnt; #endif /* * 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 'critpri' 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_pri >= TDPRI_CRIT, ("BADCRIT0 %d", ntd->td_pri)); td = gd->gd_curthread; if ((ntd->td_pri & TDPRI_MASK) <= (td->td_pri & TDPRI_MASK)) { ++preempt_miss; return; } if ((td->td_pri & ~TDPRI_MASK) > critpri) { ++preempt_miss; need_lwkt_resched(); return; } #ifdef SMP if (ntd->td_gd != gd) { ++preempt_miss; need_lwkt_resched(); return; } #endif /* * Take the easy way out and do not preempt if we are holding * any spinlocks. We could test whether the thread(s) being * preempted interlock against the target thread's tokens and whether * we can get all the target thread's tokens, but this situation * should not occur very often so its easier to simply not preempt. * Also, plain spinlocks are impossible to figure out at this point so * just don't preempt. * * 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. */ if (gd->gd_spinlock_rd || gd->gd_spinlocks_wr) { ++preempt_miss; need_lwkt_resched(); return; } if (ntd->td_toks) { ++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; } #ifdef SMP /* * note: an interrupt might have occured just as we were transitioning * to or from the MP lock. In this case td_mpcount will be pre-disposed * (non-zero) but not actually synchronized with the actual state of the * lock. We can use it to imply an MP lock requirement for the * preemption but we cannot use it to test whether we hold the MP lock * or not. */ savecnt = td->td_mpcount; mpheld = MP_LOCK_HELD(); ntd->td_mpcount += td->td_mpcount; if (mpheld == 0 && ntd->td_mpcount && !cpu_try_mplock()) { ntd->td_mpcount -= td->td_mpcount; ++preempt_miss; need_lwkt_resched(); return; } #endif /* * Since we are able to preempt the current thread, there is no need to * call need_lwkt_resched(). */ ++preempt_hit; ntd->td_preempted = td; td->td_flags |= TDF_PREEMPT_LOCK; td->td_switch(ntd); KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE)); #ifdef SMP KKASSERT(savecnt == td->td_mpcount); mpheld = MP_LOCK_HELD(); if (mpheld && td->td_mpcount == 0) cpu_rel_mplock(); else if (mpheld == 0 && td->td_mpcount) panic("lwkt_preempt(): MP lock was not held through"); #endif ntd->td_preempted = NULL; td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE); } /* * Yield our thread while higher priority threads are pending. This is * typically called when we leave a critical section but it can be safely * called while we are in a critical section. * * This function will not generally yield to equal priority threads but it * can occur as a side effect. Note that lwkt_switch() is called from * inside the critical section to prevent its own crit_exit() from reentering * lwkt_yield_quick(). * * gd_reqflags indicates that *something* changed, e.g. an interrupt or softint * came along but was blocked and made pending. * * (self contained on a per cpu basis) */ void lwkt_yield_quick(void) { globaldata_t gd = mycpu; thread_t td = gd->gd_curthread; /* * gd_reqflags is cleared in splz if the cpl is 0. If we were to clear * it with a non-zero cpl then we might not wind up calling splz after * a task switch when the critical section is exited even though the * new task could accept the interrupt. * * XXX from crit_exit() only called after last crit section is released. * If called directly will run splz() even if in a critical section. * * td_nest_count prevent deep nesting via splz() or doreti(). Note that * except for this special case, we MUST call splz() here to handle any * pending ints, particularly after we switch, or we might accidently * halt the cpu with interrupts pending. */ if (gd->gd_reqflags && td->td_nest_count < 2) splz(); /* * YYY enabling will cause wakeup() to task-switch, which really * confused the old 4.x code. This is a good way to simulate * preemption and MP without actually doing preemption or MP, because a * lot of code assumes that wakeup() does not block. */ if (untimely_switch && td->td_nest_count == 0 && gd->gd_intr_nesting_level == 0 ) { crit_enter_quick(td); /* * YYY temporary hacks until we disassociate the userland scheduler * from the LWKT scheduler. */ if (td->td_flags & TDF_RUNQ) { lwkt_switch(); /* will not reenter yield function */ } else { lwkt_schedule_self(td); /* make sure we are scheduled */ lwkt_switch(); /* will not reenter yield function */ lwkt_deschedule_self(td); /* make sure we are descheduled */ } crit_exit_noyield(td); } } /* * This implements a normal yield which, unlike _quick, will yield to equal * priority threads as well. Note that gd_reqflags tests will be handled by * the crit_exit() call in lwkt_switch(). * * (self contained on a per cpu basis) */ void lwkt_yield(void) { lwkt_schedule_self(curthread); lwkt_switch(); } /* * 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 cpri, int reschedok) { int mypri; if (ntd->td_flags & TDF_RUNQ) { if (ntd->td_preemptable && reschedok) { ntd->td_preemptable(ntd, cpri); /* YYY +token */ } else if (reschedok) { /* * This is a little sticky. Due to the passive release function * the LWKT priority can wiggle around for threads acting in * the kernel on behalf of a user process. We do not want this * to effect the comparison per-say. * * What will happen is that the current user process will be * allowed to run until the next hardclock at which time a * forced need_lwkt_resched() will allow the other kernel mode * threads to get in their two cents. This prevents cavitation. */ mypri = gd->gd_curthread->td_pri & TDPRI_MASK; if (mypri >= TDPRI_USER_IDLE && mypri <= TDPRI_USER_REAL) mypri = TDPRI_KERN_USER; if ((ntd->td_pri & TDPRI_MASK) > mypri) need_lwkt_resched(); } } } 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!")); 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, TDPRI_CRIT, reschedok); } else { lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_schedule, td); } #else _lwkt_enqueue(td); _lwkt_schedule_post(mygd, td, TDPRI_CRIT, 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 /* * 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(). * * MPSAFE - must be called under very specific conditions. */ void lwkt_giveaway(thread_t td) { globaldata_t gd = mycpu; crit_enter_gd(gd); 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); while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { #ifdef SMP lwkt_process_ipiq(); #endif cpu_lfence(); } 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. * * We have to retain the critical section count which uses the high bits * of the td_pri field. The specified priority may also indicate zero or * more critical sections by adding TDPRI_CRIT*N. * * Note that we requeue the thread whether it winds up on a different runq * or not. uio_yield() depends on this and the routine is not normally * called with the same priority otherwise. */ void lwkt_setpri(thread_t td, int pri) { KKASSERT(pri >= 0); KKASSERT(td->td_gd == mycpu); crit_enter(); if (td->td_flags & TDF_RUNQ) { _lwkt_dequeue(td); td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; _lwkt_enqueue(td); } else { td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; } crit_exit(); } 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 = (td->td_pri & ~TDPRI_MASK) + pri; _lwkt_enqueue(td); } else { td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; } crit_exit(); } /* * 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. */ #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); 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; while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { #ifdef SMP lwkt_process_ipiq(); #endif cpu_lfence(); } td->td_gd = gd; cpu_sfence(); 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; if (td->td_flags & TDF_VERBOSE) kprintf("kthread %p %s has exited\n", td, td->td_comm); caps_exit(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) { gd->gd_freetd = NULL; objcache_put(thread_cache, std); } lwkt_deschedule_self(td); lwkt_remove_tdallq(td); 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); } void crit_panic(void) { thread_t td = curthread; int lpri = td->td_pri; td->td_pri = 0; panic("td_pri is/would-go negative! %p %d", td, lpri); } #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); } /* * get_mplock() calls this routine if it is unable to obtain the MP lock. * get_mplock() has already incremented td_mpcount. We must block and * not return until giant is held. * * All we have to do is lwkt_switch() away. The LWKT scheduler will not * reschedule the thread until it can obtain the giant lock for it. */ void lwkt_mp_lock_contested(void) { loggiant(beg); lwkt_switch(); loggiant(end); } #endif