2 * Copyright (c) 2003,2004 The DragonFly Project. All rights reserved.
4 * This code is derived from software contributed to The DragonFly Project
5 * by Matthew Dillon <dillon@backplane.com>
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in
15 * the documentation and/or other materials provided with the
17 * 3. Neither the name of The DragonFly Project nor the names of its
18 * contributors may be used to endorse or promote products derived
19 * from this software without specific, prior written permission.
21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
23 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
24 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
25 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
26 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
27 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
28 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
29 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
30 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
31 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
36 * Each cpu in a system has its own self-contained light weight kernel
37 * thread scheduler, which means that generally speaking we only need
38 * to use a critical section to avoid problems. Foreign thread
39 * scheduling is queued via (async) IPIs.
42 #include <sys/param.h>
43 #include <sys/systm.h>
44 #include <sys/kernel.h>
46 #include <sys/rtprio.h>
47 #include <sys/queue.h>
48 #include <sys/sysctl.h>
49 #include <sys/kthread.h>
50 #include <machine/cpu.h>
53 #include <sys/spinlock.h>
56 #include <sys/thread2.h>
57 #include <sys/spinlock2.h>
60 #include <vm/vm_param.h>
61 #include <vm/vm_kern.h>
62 #include <vm/vm_object.h>
63 #include <vm/vm_page.h>
64 #include <vm/vm_map.h>
65 #include <vm/vm_pager.h>
66 #include <vm/vm_extern.h>
68 #include <machine/stdarg.h>
69 #include <machine/smp.h>
71 #if !defined(KTR_CTXSW)
72 #define KTR_CTXSW KTR_ALL
74 KTR_INFO_MASTER(ctxsw);
75 KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "sw %p > %p", 2 * sizeof(struct thread *));
76 KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "pre %p > %p", 2 * sizeof(struct thread *));
78 static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads");
81 static int mplock_countx = 0;
84 static int panic_on_cscount = 0;
86 static __int64_t switch_count = 0;
87 static __int64_t preempt_hit = 0;
88 static __int64_t preempt_miss = 0;
89 static __int64_t preempt_weird = 0;
90 static __int64_t token_contention_count __debugvar = 0;
91 static __int64_t mplock_contention_count __debugvar = 0;
92 static int lwkt_use_spin_port;
94 static int chain_mplock = 0;
95 static int bgl_yield = 10;
97 static struct objcache *thread_cache;
99 volatile cpumask_t mp_lock_contention_mask;
102 static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame);
105 extern void cpu_heavy_restore(void);
106 extern void cpu_lwkt_restore(void);
107 extern void cpu_kthread_restore(void);
108 extern void cpu_idle_restore(void);
113 jg_tos_ok(struct thread *td)
121 KKASSERT(td->td_sp != NULL);
122 tos = ((void **)td->td_sp)[0];
124 if ((tos == cpu_heavy_restore) || (tos == cpu_lwkt_restore) ||
125 (tos == cpu_kthread_restore) || (tos == cpu_idle_restore)) {
134 * We can make all thread ports use the spin backend instead of the thread
135 * backend. This should only be set to debug the spin backend.
137 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port);
140 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0, "");
143 SYSCTL_INT(_lwkt, OID_AUTO, chain_mplock, CTLFLAG_RW, &chain_mplock, 0, "");
144 SYSCTL_INT(_lwkt, OID_AUTO, bgl_yield_delay, CTLFLAG_RW, &bgl_yield, 0, "");
146 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0, "");
147 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0, "");
148 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0, "");
149 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0, "");
151 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count, CTLFLAG_RW,
152 &token_contention_count, 0, "spinning due to token contention");
153 SYSCTL_QUAD(_lwkt, OID_AUTO, mplock_contention_count, CTLFLAG_RW,
154 &mplock_contention_count, 0, "spinning due to MPLOCK contention");
160 #if !defined(KTR_GIANT_CONTENTION)
161 #define KTR_GIANT_CONTENTION KTR_ALL
164 KTR_INFO_MASTER(giant);
165 KTR_INFO(KTR_GIANT_CONTENTION, giant, beg, 0, "thread=%p", sizeof(void *));
166 KTR_INFO(KTR_GIANT_CONTENTION, giant, end, 1, "thread=%p", sizeof(void *));
168 #define loggiant(name) KTR_LOG(giant_ ## name, curthread)
171 * These helper procedures handle the runq, they can only be called from
172 * within a critical section.
174 * WARNING! Prior to SMP being brought up it is possible to enqueue and
175 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
176 * instead of 'mycpu' when referencing the globaldata structure. Once
177 * SMP live enqueuing and dequeueing only occurs on the current cpu.
181 _lwkt_dequeue(thread_t td)
183 if (td->td_flags & TDF_RUNQ) {
184 int nq = td->td_pri & TDPRI_MASK;
185 struct globaldata *gd = td->td_gd;
187 td->td_flags &= ~TDF_RUNQ;
188 TAILQ_REMOVE(&gd->gd_tdrunq[nq], td, td_threadq);
189 /* runqmask is passively cleaned up by the switcher */
195 _lwkt_enqueue(thread_t td)
197 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) {
198 int nq = td->td_pri & TDPRI_MASK;
199 struct globaldata *gd = td->td_gd;
201 td->td_flags |= TDF_RUNQ;
202 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], td, td_threadq);
203 gd->gd_runqmask |= 1 << nq;
208 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags)
210 struct thread *td = (struct thread *)obj;
212 td->td_kstack = NULL;
213 td->td_kstack_size = 0;
214 td->td_flags = TDF_ALLOCATED_THREAD;
219 _lwkt_thread_dtor(void *obj, void *privdata)
221 struct thread *td = (struct thread *)obj;
223 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
224 ("_lwkt_thread_dtor: not allocated from objcache"));
225 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
226 td->td_kstack_size > 0,
227 ("_lwkt_thread_dtor: corrupted stack"));
228 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
232 * Initialize the lwkt s/system.
237 /* An objcache has 2 magazines per CPU so divide cache size by 2. */
238 thread_cache = objcache_create_mbacked(M_THREAD, sizeof(struct thread),
239 NULL, CACHE_NTHREADS/2,
240 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
244 * Schedule a thread to run. As the current thread we can always safely
245 * schedule ourselves, and a shortcut procedure is provided for that
248 * (non-blocking, self contained on a per cpu basis)
251 lwkt_schedule_self(thread_t td)
253 crit_enter_quick(td);
254 KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
255 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
261 * Deschedule a thread.
263 * (non-blocking, self contained on a per cpu basis)
266 lwkt_deschedule_self(thread_t td)
268 crit_enter_quick(td);
274 * LWKTs operate on a per-cpu basis
276 * WARNING! Called from early boot, 'mycpu' may not work yet.
279 lwkt_gdinit(struct globaldata *gd)
283 for (i = 0; i < sizeof(gd->gd_tdrunq)/sizeof(gd->gd_tdrunq[0]); ++i)
284 TAILQ_INIT(&gd->gd_tdrunq[i]);
286 TAILQ_INIT(&gd->gd_tdallq);
290 * Create a new thread. The thread must be associated with a process context
291 * or LWKT start address before it can be scheduled. If the target cpu is
292 * -1 the thread will be created on the current cpu.
294 * If you intend to create a thread without a process context this function
295 * does everything except load the startup and switcher function.
298 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
300 globaldata_t gd = mycpu;
304 * If static thread storage is not supplied allocate a thread. Reuse
305 * a cached free thread if possible. gd_freetd is used to keep an exiting
306 * thread intact through the exit.
309 if ((td = gd->gd_freetd) != NULL)
310 gd->gd_freetd = NULL;
312 td = objcache_get(thread_cache, M_WAITOK);
313 KASSERT((td->td_flags &
314 (TDF_ALLOCATED_THREAD|TDF_RUNNING)) == TDF_ALLOCATED_THREAD,
315 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
316 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
320 * Try to reuse cached stack.
322 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
323 if (flags & TDF_ALLOCATED_STACK) {
324 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
329 stack = (void *)kmem_alloc(&kernel_map, stksize);
330 flags |= TDF_ALLOCATED_STACK;
333 lwkt_init_thread(td, stack, stksize, flags, gd);
335 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
340 * Initialize a preexisting thread structure. This function is used by
341 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
343 * All threads start out in a critical section at a priority of
344 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
345 * appropriate. This function may send an IPI message when the
346 * requested cpu is not the current cpu and consequently gd_tdallq may
347 * not be initialized synchronously from the point of view of the originating
350 * NOTE! we have to be careful in regards to creating threads for other cpus
351 * if SMP has not yet been activated.
356 lwkt_init_thread_remote(void *arg)
361 * Protected by critical section held by IPI dispatch
363 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
369 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
370 struct globaldata *gd)
372 globaldata_t mygd = mycpu;
374 bzero(td, sizeof(struct thread));
375 td->td_kstack = stack;
376 td->td_kstack_size = stksize;
377 td->td_flags = flags;
379 td->td_pri = TDPRI_KERN_DAEMON + TDPRI_CRIT;
381 if ((flags & TDF_MPSAFE) == 0)
384 if (lwkt_use_spin_port)
385 lwkt_initport_spin(&td->td_msgport);
387 lwkt_initport_thread(&td->td_msgport, td);
388 pmap_init_thread(td);
391 * Normally initializing a thread for a remote cpu requires sending an
392 * IPI. However, the idlethread is setup before the other cpus are
393 * activated so we have to treat it as a special case. XXX manipulation
394 * of gd_tdallq requires the BGL.
396 if (gd == mygd || td == &gd->gd_idlethread) {
398 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
401 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
405 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
411 lwkt_set_comm(thread_t td, const char *ctl, ...)
416 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
421 lwkt_hold(thread_t td)
427 lwkt_rele(thread_t td)
429 KKASSERT(td->td_refs > 0);
434 lwkt_wait_free(thread_t td)
437 tsleep(td, 0, "tdreap", hz);
441 lwkt_free_thread(thread_t td)
443 KASSERT((td->td_flags & TDF_RUNNING) == 0,
444 ("lwkt_free_thread: did not exit! %p", td));
446 if (td->td_flags & TDF_ALLOCATED_THREAD) {
447 objcache_put(thread_cache, td);
448 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
449 /* client-allocated struct with internally allocated stack */
450 KASSERT(td->td_kstack && td->td_kstack_size > 0,
451 ("lwkt_free_thread: corrupted stack"));
452 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
453 td->td_kstack = NULL;
454 td->td_kstack_size = 0;
460 * Switch to the next runnable lwkt. If no LWKTs are runnable then
461 * switch to the idlethread. Switching must occur within a critical
462 * section to avoid races with the scheduling queue.
464 * We always have full control over our cpu's run queue. Other cpus
465 * that wish to manipulate our queue must use the cpu_*msg() calls to
466 * talk to our cpu, so a critical section is all that is needed and
467 * the result is very, very fast thread switching.
469 * The LWKT scheduler uses a fixed priority model and round-robins at
470 * each priority level. User process scheduling is a totally
471 * different beast and LWKT priorities should not be confused with
472 * user process priorities.
474 * The MP lock may be out of sync with the thread's td_mpcount. lwkt_switch()
475 * cleans it up. Note that the td_switch() function cannot do anything that
476 * requires the MP lock since the MP lock will have already been setup for
477 * the target thread (not the current thread). It's nice to have a scheduler
478 * that does not need the MP lock to work because it allows us to do some
479 * really cool high-performance MP lock optimizations.
481 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
482 * is not called by the current thread in the preemption case, only when
483 * the preempting thread blocks (in order to return to the original thread).
488 globaldata_t gd = mycpu;
489 thread_t td = gd->gd_curthread;
496 * Switching from within a 'fast' (non thread switched) interrupt or IPI
497 * is illegal. However, we may have to do it anyway if we hit a fatal
498 * kernel trap or we have paniced.
500 * If this case occurs save and restore the interrupt nesting level.
502 if (gd->gd_intr_nesting_level) {
506 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) {
507 panic("lwkt_switch: cannot switch from within "
508 "a fast interrupt, yet, td %p\n", td);
510 savegdnest = gd->gd_intr_nesting_level;
511 savegdtrap = gd->gd_trap_nesting_level;
512 gd->gd_intr_nesting_level = 0;
513 gd->gd_trap_nesting_level = 0;
514 if ((td->td_flags & TDF_PANICWARN) == 0) {
515 td->td_flags |= TDF_PANICWARN;
516 kprintf("Warning: thread switch from interrupt or IPI, "
517 "thread %p (%s)\n", td, td->td_comm);
521 gd->gd_intr_nesting_level = savegdnest;
522 gd->gd_trap_nesting_level = savegdtrap;
528 * Passive release (used to transition from user to kernel mode
529 * when we block or switch rather then when we enter the kernel).
530 * This function is NOT called if we are switching into a preemption
531 * or returning from a preemption. Typically this causes us to lose
532 * our current process designation (if we have one) and become a true
533 * LWKT thread, and may also hand the current process designation to
534 * another process and schedule thread.
541 lwkt_relalltokens(td);
544 * We had better not be holding any spin locks, but don't get into an
545 * endless panic loop.
547 KASSERT(gd->gd_spinlock_rd == NULL || panicstr != NULL,
548 ("lwkt_switch: still holding a shared spinlock %p!",
549 gd->gd_spinlock_rd));
550 KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL,
551 ("lwkt_switch: still holding %d exclusive spinlocks!",
552 gd->gd_spinlocks_wr));
557 * td_mpcount cannot be used to determine if we currently hold the
558 * MP lock because get_mplock() will increment it prior to attempting
559 * to get the lock, and switch out if it can't. Our ownership of
560 * the actual lock will remain stable while we are in a critical section
561 * (but, of course, another cpu may own or release the lock so the
562 * actual value of mp_lock is not stable).
564 mpheld = MP_LOCK_HELD();
566 if (td->td_cscount) {
567 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
569 if (panic_on_cscount)
570 panic("switching while mastering cpusync");
574 if ((ntd = td->td_preempted) != NULL) {
576 * We had preempted another thread on this cpu, resume the preempted
577 * thread. This occurs transparently, whether the preempted thread
578 * was scheduled or not (it may have been preempted after descheduling
581 * We have to setup the MP lock for the original thread after backing
582 * out the adjustment that was made to curthread when the original
585 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
587 if (ntd->td_mpcount && mpheld == 0) {
588 panic("MPLOCK NOT HELD ON RETURN: %p %p %d %d",
589 td, ntd, td->td_mpcount, ntd->td_mpcount);
591 if (ntd->td_mpcount) {
592 td->td_mpcount -= ntd->td_mpcount;
593 KKASSERT(td->td_mpcount >= 0);
596 ntd->td_flags |= TDF_PREEMPT_DONE;
599 * The interrupt may have woken a thread up, we need to properly
600 * set the reschedule flag if the originally interrupted thread is
601 * at a lower priority.
603 if (gd->gd_runqmask > (2 << (ntd->td_pri & TDPRI_MASK)) - 1)
605 /* YYY release mp lock on switchback if original doesn't need it */
608 * Priority queue / round-robin at each priority. Note that user
609 * processes run at a fixed, low priority and the user process
610 * scheduler deals with interactions between user processes
611 * by scheduling and descheduling them from the LWKT queue as
614 * We have to adjust the MP lock for the target thread. If we
615 * need the MP lock and cannot obtain it we try to locate a
616 * thread that does not need the MP lock. If we cannot, we spin
619 * A similar issue exists for the tokens held by the target thread.
620 * If we cannot obtain ownership of the tokens we cannot immediately
621 * schedule the thread.
625 * If an LWKT reschedule was requested, well that is what we are
626 * doing now so clear it.
628 clear_lwkt_resched();
630 if (gd->gd_runqmask) {
631 int nq = bsrl(gd->gd_runqmask);
632 if ((ntd = TAILQ_FIRST(&gd->gd_tdrunq[nq])) == NULL) {
633 gd->gd_runqmask &= ~(1 << nq);
638 * THREAD SELECTION FOR AN SMP MACHINE BUILD
640 * If the target needs the MP lock and we couldn't get it,
641 * or if the target is holding tokens and we could not
642 * gain ownership of the tokens, continue looking for a
643 * thread to schedule and spin instead of HLT if we can't.
645 * NOTE: the mpheld variable invalid after this conditional, it
646 * can change due to both cpu_try_mplock() returning success
647 * AND interactions in lwkt_getalltokens() due to the fact that
648 * we are trying to check the mpcount of a thread other then
649 * the current thread. Because of this, if the current thread
650 * is not holding td_mpcount, an IPI indirectly run via
651 * lwkt_getalltokens() can obtain and release the MP lock and
652 * cause the core MP lock to be released.
654 if ((ntd->td_mpcount && mpheld == 0 && !cpu_try_mplock()) ||
655 (ntd->td_toks && lwkt_getalltokens(ntd) == 0)
657 u_int32_t rqmask = gd->gd_runqmask;
659 mpheld = MP_LOCK_HELD();
662 TAILQ_FOREACH(ntd, &gd->gd_tdrunq[nq], td_threadq) {
663 if (ntd->td_mpcount && !mpheld && !cpu_try_mplock()) {
664 /* spinning due to MP lock being held */
666 ++mplock_contention_count;
668 /* mplock still not held, 'mpheld' still valid */
673 * mpheld state invalid after getalltokens call returns
674 * failure, but the variable is only needed for
677 if (ntd->td_toks && !lwkt_getalltokens(ntd)) {
678 /* spinning due to token contention */
680 ++token_contention_count;
682 mpheld = MP_LOCK_HELD();
689 rqmask &= ~(1 << nq);
693 * We have two choices. We can either refuse to run a
694 * user thread when a kernel thread needs the MP lock
695 * but could not get it, or we can allow it to run but
696 * then expect an IPI (hopefully) later on to force a
697 * reschedule when the MP lock might become available.
699 if (nq < TDPRI_KERN_LPSCHED) {
700 if (chain_mplock == 0)
702 atomic_set_int(&mp_lock_contention_mask,
704 /* continue loop, allow user threads to be scheduled */
708 cpu_mplock_contested();
709 ntd = &gd->gd_idlethread;
710 ntd->td_flags |= TDF_IDLE_NOHLT;
711 goto using_idle_thread;
713 ++gd->gd_cnt.v_swtch;
714 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq);
715 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq);
720 ++gd->gd_cnt.v_swtch;
721 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq);
722 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq);
726 * THREAD SELECTION FOR A UP MACHINE BUILD. We don't have to
727 * worry about tokens or the BGL. However, we still have
728 * to call lwkt_getalltokens() in order to properly detect
729 * stale tokens. This call cannot fail for a UP build!
731 lwkt_getalltokens(ntd);
732 ++gd->gd_cnt.v_swtch;
733 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq);
734 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq);
738 * We have nothing to run but only let the idle loop halt
739 * the cpu if there are no pending interrupts.
741 ntd = &gd->gd_idlethread;
742 if (gd->gd_reqflags & RQF_IDLECHECK_MASK)
743 ntd->td_flags |= TDF_IDLE_NOHLT;
747 * The idle thread should not be holding the MP lock unless we
748 * are trapping in the kernel or in a panic. Since we select the
749 * idle thread unconditionally when no other thread is available,
750 * if the MP lock is desired during a panic or kernel trap, we
751 * have to loop in the scheduler until we get it.
753 if (ntd->td_mpcount) {
754 mpheld = MP_LOCK_HELD();
755 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) {
756 panic("Idle thread %p was holding the BGL!", ntd);
757 } else if (mpheld == 0) {
758 cpu_mplock_contested();
765 KASSERT(ntd->td_pri >= TDPRI_CRIT,
766 ("priority problem in lwkt_switch %d %d", td->td_pri, ntd->td_pri));
769 * Do the actual switch. If the new target does not need the MP lock
770 * and we are holding it, release the MP lock. If the new target requires
771 * the MP lock we have already acquired it for the target.
774 if (ntd->td_mpcount == 0 ) {
778 ASSERT_MP_LOCK_HELD(ntd);
785 int tos_ok __debugvar = jg_tos_ok(ntd);
789 KTR_LOG(ctxsw_sw, td, ntd);
792 /* NOTE: current cpu may have changed after switch */
797 * Request that the target thread preempt the current thread. Preemption
798 * only works under a specific set of conditions:
800 * - We are not preempting ourselves
801 * - The target thread is owned by the current cpu
802 * - We are not currently being preempted
803 * - The target is not currently being preempted
804 * - We are not holding any spin locks
805 * - The target thread is not holding any tokens
806 * - We are able to satisfy the target's MP lock requirements (if any).
808 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
809 * this is called via lwkt_schedule() through the td_preemptable callback.
810 * critpri is the managed critical priority that we should ignore in order
811 * to determine whether preemption is possible (aka usually just the crit
812 * priority of lwkt_schedule() itself).
814 * XXX at the moment we run the target thread in a critical section during
815 * the preemption in order to prevent the target from taking interrupts
816 * that *WE* can't. Preemption is strictly limited to interrupt threads
817 * and interrupt-like threads, outside of a critical section, and the
818 * preempted source thread will be resumed the instant the target blocks
819 * whether or not the source is scheduled (i.e. preemption is supposed to
820 * be as transparent as possible).
822 * The target thread inherits our MP count (added to its own) for the
823 * duration of the preemption in order to preserve the atomicy of the
824 * MP lock during the preemption. Therefore, any preempting targets must be
825 * careful in regards to MP assertions. Note that the MP count may be
826 * out of sync with the physical mp_lock, but we do not have to preserve
827 * the original ownership of the lock if it was out of synch (that is, we
828 * can leave it synchronized on return).
831 lwkt_preempt(thread_t ntd, int critpri)
833 struct globaldata *gd = mycpu;
841 * The caller has put us in a critical section. We can only preempt
842 * if the caller of the caller was not in a critical section (basically
843 * a local interrupt), as determined by the 'critpri' parameter. We
844 * also can't preempt if the caller is holding any spinlocks (even if
845 * he isn't in a critical section). This also handles the tokens test.
847 * YYY The target thread must be in a critical section (else it must
848 * inherit our critical section? I dunno yet).
850 * Set need_lwkt_resched() unconditionally for now YYY.
852 KASSERT(ntd->td_pri >= TDPRI_CRIT, ("BADCRIT0 %d", ntd->td_pri));
854 td = gd->gd_curthread;
855 if ((ntd->td_pri & TDPRI_MASK) <= (td->td_pri & TDPRI_MASK)) {
859 if ((td->td_pri & ~TDPRI_MASK) > critpri) {
865 if (ntd->td_gd != gd) {
872 * Take the easy way out and do not preempt if we are holding
873 * any spinlocks. We could test whether the thread(s) being
874 * preempted interlock against the target thread's tokens and whether
875 * we can get all the target thread's tokens, but this situation
876 * should not occur very often so its easier to simply not preempt.
877 * Also, plain spinlocks are impossible to figure out at this point so
878 * just don't preempt.
880 * Do not try to preempt if the target thread is holding any tokens.
881 * We could try to acquire the tokens but this case is so rare there
882 * is no need to support it.
884 if (gd->gd_spinlock_rd || gd->gd_spinlocks_wr) {
894 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
899 if (ntd->td_preempted) {
906 * note: an interrupt might have occured just as we were transitioning
907 * to or from the MP lock. In this case td_mpcount will be pre-disposed
908 * (non-zero) but not actually synchronized with the actual state of the
909 * lock. We can use it to imply an MP lock requirement for the
910 * preemption but we cannot use it to test whether we hold the MP lock
913 savecnt = td->td_mpcount;
914 mpheld = MP_LOCK_HELD();
915 ntd->td_mpcount += td->td_mpcount;
916 if (mpheld == 0 && ntd->td_mpcount && !cpu_try_mplock()) {
917 ntd->td_mpcount -= td->td_mpcount;
925 * Since we are able to preempt the current thread, there is no need to
926 * call need_lwkt_resched().
929 ntd->td_preempted = td;
930 td->td_flags |= TDF_PREEMPT_LOCK;
931 KTR_LOG(ctxsw_pre, td, ntd);
934 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
936 KKASSERT(savecnt == td->td_mpcount);
937 mpheld = MP_LOCK_HELD();
938 if (mpheld && td->td_mpcount == 0)
940 else if (mpheld == 0 && td->td_mpcount)
941 panic("lwkt_preempt(): MP lock was not held through");
943 ntd->td_preempted = NULL;
944 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
948 * Conditionally call splz() if gd_reqflags indicates work is pending.
950 * td_nest_count prevents deep nesting via splz() or doreti() which
951 * might otherwise blow out the kernel stack. Note that except for
952 * this special case, we MUST call splz() here to handle any
953 * pending ints, particularly after we switch, or we might accidently
954 * halt the cpu with interrupts pending.
956 * (self contained on a per cpu basis)
961 globaldata_t gd = mycpu;
962 thread_t td = gd->gd_curthread;
964 if (gd->gd_reqflags && td->td_nest_count < 2)
969 * This implements a normal yield which will yield to equal priority
970 * threads as well as higher priority threads. Note that gd_reqflags
971 * tests will be handled by the crit_exit() call in lwkt_switch().
973 * (self contained on a per cpu basis)
978 lwkt_schedule_self(curthread);
983 * This function is used along with the lwkt_passive_recover() inline
984 * by the trap code to negotiate a passive release of the current
985 * process/lwp designation with the user scheduler.
988 lwkt_passive_release(struct thread *td)
990 struct lwp *lp = td->td_lwp;
992 td->td_release = NULL;
993 lwkt_setpri_self(TDPRI_KERN_USER);
994 lp->lwp_proc->p_usched->release_curproc(lp);
998 * Make a kernel thread act as if it were in user mode with regards
999 * to scheduling, to avoid becoming cpu-bound in the kernel. Kernel
1000 * loops which may be potentially cpu-bound can call lwkt_user_yield().
1002 * The lwkt_user_yield() function is designed to have very low overhead
1003 * if no yield is determined to be needed.
1006 lwkt_user_yield(void)
1008 thread_t td = curthread;
1009 struct lwp *lp = td->td_lwp;
1013 * XXX SEVERE TEMPORARY HACK. A cpu-bound operation running in the
1014 * kernel can prevent other cpus from servicing interrupt threads
1015 * which still require the MP lock (which is a lot of them). This
1016 * has a chaining effect since if the interrupt is blocked, so is
1017 * the event, so normal scheduling will not pick up on the problem.
1019 if (mplock_countx && td->td_mpcount) {
1020 int savecnt = td->td_mpcount;
1027 td->td_mpcount = savecnt;
1032 * Another kernel thread wants the cpu
1034 if (lwkt_resched_wanted())
1038 * If the user scheduler has asynchronously determined that the current
1039 * process (when running in user mode) needs to lose the cpu then make
1040 * sure we are released.
1042 if (user_resched_wanted()) {
1048 * If we are released reduce our priority
1050 if (td->td_release == NULL) {
1051 if (lwkt_check_resched(td) > 0)
1054 lp->lwp_proc->p_usched->acquire_curproc(lp);
1055 td->td_release = lwkt_passive_release;
1056 lwkt_setpri_self(TDPRI_USER_NORM);
1062 * Return 0 if no runnable threads are pending at the same or higher
1063 * priority as the passed thread.
1065 * Return 1 if runnable threads are pending at the same priority.
1067 * Return 2 if runnable threads are pending at a higher priority.
1070 lwkt_check_resched(thread_t td)
1072 int pri = td->td_pri & TDPRI_MASK;
1074 if (td->td_gd->gd_runqmask > (2 << pri) - 1)
1076 if (TAILQ_NEXT(td, td_threadq))
1082 * Generic schedule. Possibly schedule threads belonging to other cpus and
1083 * deal with threads that might be blocked on a wait queue.
1085 * We have a little helper inline function which does additional work after
1086 * the thread has been enqueued, including dealing with preemption and
1087 * setting need_lwkt_resched() (which prevents the kernel from returning
1088 * to userland until it has processed higher priority threads).
1090 * It is possible for this routine to be called after a failed _enqueue
1091 * (due to the target thread migrating, sleeping, or otherwise blocked).
1092 * We have to check that the thread is actually on the run queue!
1094 * reschedok is an optimized constant propagated from lwkt_schedule() or
1095 * lwkt_schedule_noresched(). By default it is non-zero, causing a
1096 * reschedule to be requested if the target thread has a higher priority.
1097 * The port messaging code will set MSG_NORESCHED and cause reschedok to
1098 * be 0, prevented undesired reschedules.
1102 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int cpri, int reschedok)
1106 if (ntd->td_flags & TDF_RUNQ) {
1107 if (ntd->td_preemptable && reschedok) {
1108 ntd->td_preemptable(ntd, cpri); /* YYY +token */
1109 } else if (reschedok) {
1111 if ((ntd->td_pri & TDPRI_MASK) > (otd->td_pri & TDPRI_MASK))
1112 need_lwkt_resched();
1119 _lwkt_schedule(thread_t td, int reschedok)
1121 globaldata_t mygd = mycpu;
1123 KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
1124 crit_enter_gd(mygd);
1125 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
1126 if (td == mygd->gd_curthread) {
1130 * If we own the thread, there is no race (since we are in a
1131 * critical section). If we do not own the thread there might
1132 * be a race but the target cpu will deal with it.
1135 if (td->td_gd == mygd) {
1137 _lwkt_schedule_post(mygd, td, TDPRI_CRIT, reschedok);
1139 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
1143 _lwkt_schedule_post(mygd, td, TDPRI_CRIT, reschedok);
1150 lwkt_schedule(thread_t td)
1152 _lwkt_schedule(td, 1);
1156 lwkt_schedule_noresched(thread_t td)
1158 _lwkt_schedule(td, 0);
1164 * When scheduled remotely if frame != NULL the IPIQ is being
1165 * run via doreti or an interrupt then preemption can be allowed.
1167 * To allow preemption we have to drop the critical section so only
1168 * one is present in _lwkt_schedule_post.
1171 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1173 thread_t td = curthread;
1176 if (frame && ntd->td_preemptable) {
1177 crit_exit_noyield(td);
1178 _lwkt_schedule(ntd, 1);
1179 crit_enter_quick(td);
1181 _lwkt_schedule(ntd, 1);
1186 * Thread migration using a 'Pull' method. The thread may or may not be
1187 * the current thread. It MUST be descheduled and in a stable state.
1188 * lwkt_giveaway() must be called on the cpu owning the thread.
1190 * At any point after lwkt_giveaway() is called, the target cpu may
1191 * 'pull' the thread by calling lwkt_acquire().
1193 * We have to make sure the thread is not sitting on a per-cpu tsleep
1194 * queue or it will blow up when it moves to another cpu.
1196 * MPSAFE - must be called under very specific conditions.
1199 lwkt_giveaway(thread_t td)
1201 globaldata_t gd = mycpu;
1204 if (td->td_flags & TDF_TSLEEPQ)
1206 KKASSERT(td->td_gd == gd);
1207 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1208 td->td_flags |= TDF_MIGRATING;
1213 lwkt_acquire(thread_t td)
1218 KKASSERT(td->td_flags & TDF_MIGRATING);
1223 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1224 crit_enter_gd(mygd);
1225 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1227 lwkt_process_ipiq();
1232 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1233 td->td_flags &= ~TDF_MIGRATING;
1236 crit_enter_gd(mygd);
1237 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1238 td->td_flags &= ~TDF_MIGRATING;
1246 * Generic deschedule. Descheduling threads other then your own should be
1247 * done only in carefully controlled circumstances. Descheduling is
1250 * This function may block if the cpu has run out of messages.
1253 lwkt_deschedule(thread_t td)
1257 if (td == curthread) {
1260 if (td->td_gd == mycpu) {
1263 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
1273 * Set the target thread's priority. This routine does not automatically
1274 * switch to a higher priority thread, LWKT threads are not designed for
1275 * continuous priority changes. Yield if you want to switch.
1277 * We have to retain the critical section count which uses the high bits
1278 * of the td_pri field. The specified priority may also indicate zero or
1279 * more critical sections by adding TDPRI_CRIT*N.
1281 * Note that we requeue the thread whether it winds up on a different runq
1282 * or not. uio_yield() depends on this and the routine is not normally
1283 * called with the same priority otherwise.
1286 lwkt_setpri(thread_t td, int pri)
1289 KKASSERT(td->td_gd == mycpu);
1291 if (td->td_flags & TDF_RUNQ) {
1293 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
1296 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
1302 * Set the initial priority for a thread prior to it being scheduled for
1303 * the first time. The thread MUST NOT be scheduled before or during
1304 * this call. The thread may be assigned to a cpu other then the current
1307 * Typically used after a thread has been created with TDF_STOPPREQ,
1308 * and before the thread is initially scheduled.
1311 lwkt_setpri_initial(thread_t td, int pri)
1314 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1315 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
1319 lwkt_setpri_self(int pri)
1321 thread_t td = curthread;
1323 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1325 if (td->td_flags & TDF_RUNQ) {
1327 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
1330 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
1336 * Migrate the current thread to the specified cpu.
1338 * This is accomplished by descheduling ourselves from the current cpu,
1339 * moving our thread to the tdallq of the target cpu, IPI messaging the
1340 * target cpu, and switching out. TDF_MIGRATING prevents scheduling
1341 * races while the thread is being migrated.
1343 * We must be sure to remove ourselves from the current cpu's tsleepq
1344 * before potentially moving to another queue. The thread can be on
1345 * a tsleepq due to a left-over tsleep_interlock().
1348 static void lwkt_setcpu_remote(void *arg);
1352 lwkt_setcpu_self(globaldata_t rgd)
1355 thread_t td = curthread;
1357 if (td->td_gd != rgd) {
1358 crit_enter_quick(td);
1359 if (td->td_flags & TDF_TSLEEPQ)
1361 td->td_flags |= TDF_MIGRATING;
1362 lwkt_deschedule_self(td);
1363 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1364 lwkt_send_ipiq(rgd, (ipifunc1_t)lwkt_setcpu_remote, td);
1366 /* we are now on the target cpu */
1367 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
1368 crit_exit_quick(td);
1374 lwkt_migratecpu(int cpuid)
1379 rgd = globaldata_find(cpuid);
1380 lwkt_setcpu_self(rgd);
1385 * Remote IPI for cpu migration (called while in a critical section so we
1386 * do not have to enter another one). The thread has already been moved to
1387 * our cpu's allq, but we must wait for the thread to be completely switched
1388 * out on the originating cpu before we schedule it on ours or the stack
1389 * state may be corrupt. We clear TDF_MIGRATING after flushing the GD
1390 * change to main memory.
1392 * XXX The use of TDF_MIGRATING might not be sufficient to avoid races
1393 * against wakeups. It is best if this interface is used only when there
1394 * are no pending events that might try to schedule the thread.
1398 lwkt_setcpu_remote(void *arg)
1401 globaldata_t gd = mycpu;
1403 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1405 lwkt_process_ipiq();
1411 td->td_flags &= ~TDF_MIGRATING;
1412 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
1418 lwkt_preempted_proc(void)
1420 thread_t td = curthread;
1421 while (td->td_preempted)
1422 td = td->td_preempted;
1427 * Create a kernel process/thread/whatever. It shares it's address space
1428 * with proc0 - ie: kernel only.
1430 * NOTE! By default new threads are created with the MP lock held. A
1431 * thread which does not require the MP lock should release it by calling
1432 * rel_mplock() at the start of the new thread.
1435 lwkt_create(void (*func)(void *), void *arg,
1436 struct thread **tdp, thread_t template, int tdflags, int cpu,
1437 const char *fmt, ...)
1442 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
1446 cpu_set_thread_handler(td, lwkt_exit, func, arg);
1449 * Set up arg0 for 'ps' etc
1451 __va_start(ap, fmt);
1452 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1456 * Schedule the thread to run
1458 if ((td->td_flags & TDF_STOPREQ) == 0)
1461 td->td_flags &= ~TDF_STOPREQ;
1466 * Destroy an LWKT thread. Warning! This function is not called when
1467 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1468 * uses a different reaping mechanism.
1473 thread_t td = curthread;
1477 if (td->td_flags & TDF_VERBOSE)
1478 kprintf("kthread %p %s has exited\n", td, td->td_comm);
1482 * Get us into a critical section to interlock gd_freetd and loop
1483 * until we can get it freed.
1485 * We have to cache the current td in gd_freetd because objcache_put()ing
1486 * it would rip it out from under us while our thread is still active.
1489 crit_enter_quick(td);
1490 while ((std = gd->gd_freetd) != NULL) {
1491 gd->gd_freetd = NULL;
1492 objcache_put(thread_cache, std);
1496 * Remove thread resources from kernel lists and deschedule us for
1499 if (td->td_flags & TDF_TSLEEPQ)
1502 lwkt_deschedule_self(td);
1503 lwkt_remove_tdallq(td);
1504 if (td->td_flags & TDF_ALLOCATED_THREAD)
1510 lwkt_remove_tdallq(thread_t td)
1512 KKASSERT(td->td_gd == mycpu);
1513 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1519 thread_t td = curthread;
1520 int lpri = td->td_pri;
1523 panic("td_pri is/would-go negative! %p %d", td, lpri);
1529 * Called from debugger/panic on cpus which have been stopped. We must still
1530 * process the IPIQ while stopped, even if we were stopped while in a critical
1533 * If we are dumping also try to process any pending interrupts. This may
1534 * or may not work depending on the state of the cpu at the point it was
1538 lwkt_smp_stopped(void)
1540 globaldata_t gd = mycpu;
1544 lwkt_process_ipiq();
1547 lwkt_process_ipiq();
1553 * get_mplock() calls this routine if it is unable to obtain the MP lock.
1554 * get_mplock() has already incremented td_mpcount. We must block and
1555 * not return until giant is held.
1557 * All we have to do is lwkt_switch() away. The LWKT scheduler will not
1558 * reschedule the thread until it can obtain the giant lock for it.
1561 lwkt_mp_lock_contested(void)
1570 * The rel_mplock() code will call this function after releasing the
1571 * last reference on the MP lock if mp_lock_contention_mask is non-zero.
1573 * We then chain an IPI to a single other cpu potentially needing the
1574 * lock. This is a bit heuristical and we can wind up with IPIs flying
1575 * all over the place.
1577 static void lwkt_mp_lock_uncontested_remote(void *arg __unused);
1580 lwkt_mp_lock_uncontested(void)
1590 atomic_clear_int(&mp_lock_contention_mask, gd->gd_cpumask);
1591 mask = mp_lock_contention_mask;
1592 tmpmask = ~((1 << gd->gd_cpuid) - 1);
1596 cpuid = bsfl(mask & tmpmask);
1599 atomic_clear_int(&mp_lock_contention_mask, 1 << cpuid);
1600 dgd = globaldata_find(cpuid);
1601 lwkt_send_ipiq(dgd, lwkt_mp_lock_uncontested_remote, NULL);
1607 * The idea is for this IPI to interrupt a potentially lower priority
1608 * thread, such as a user thread, to allow the scheduler to reschedule
1609 * a higher priority kernel thread that needs the MP lock.
1611 * For now we set the LWKT reschedule flag which generates an AST in
1612 * doreti, though theoretically it is also possible to possibly preempt
1613 * here if the underlying thread was operating in user mode. Nah.
1616 lwkt_mp_lock_uncontested_remote(void *arg __unused)
1618 need_lwkt_resched();