2 * Copyright (c) 2003-2011 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/kinfo.h>
48 #include <sys/queue.h>
49 #include <sys/sysctl.h>
50 #include <sys/kthread.h>
51 #include <machine/cpu.h>
53 #include <sys/spinlock.h>
56 #include <sys/thread2.h>
57 #include <sys/spinlock2.h>
59 #include <sys/dsched.h>
62 #include <vm/vm_param.h>
63 #include <vm/vm_kern.h>
64 #include <vm/vm_object.h>
65 #include <vm/vm_page.h>
66 #include <vm/vm_map.h>
67 #include <vm/vm_pager.h>
68 #include <vm/vm_extern.h>
70 #include <machine/stdarg.h>
71 #include <machine/smp.h>
72 #include <machine/clock.h>
74 #ifdef _KERNEL_VIRTUAL
80 #if !defined(KTR_CTXSW)
81 #define KTR_CTXSW KTR_ALL
83 KTR_INFO_MASTER(ctxsw
);
84 KTR_INFO(KTR_CTXSW
, ctxsw
, sw
, 0, "#cpu[%d].td = %p", int cpu
, struct thread
*td
);
85 KTR_INFO(KTR_CTXSW
, ctxsw
, pre
, 1, "#cpu[%d].td = %p", int cpu
, struct thread
*td
);
86 KTR_INFO(KTR_CTXSW
, ctxsw
, newtd
, 2, "#threads[%p].name = %s", struct thread
*td
, char *comm
);
87 KTR_INFO(KTR_CTXSW
, ctxsw
, deadtd
, 3, "#threads[%p].name = <dead>", struct thread
*td
);
89 static MALLOC_DEFINE(M_THREAD
, "thread", "lwkt threads");
92 static int panic_on_cscount
= 0;
94 static int64_t switch_count
= 0;
95 static int64_t preempt_hit
= 0;
96 static int64_t preempt_miss
= 0;
97 static int64_t preempt_weird
= 0;
98 static int lwkt_use_spin_port
;
99 static struct objcache
*thread_cache
;
100 int cpu_mwait_spin
= 0;
102 static void lwkt_schedule_remote(void *arg
, int arg2
, struct intrframe
*frame
);
103 static void lwkt_setcpu_remote(void *arg
);
106 * We can make all thread ports use the spin backend instead of the thread
107 * backend. This should only be set to debug the spin backend.
109 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port
);
112 SYSCTL_INT(_lwkt
, OID_AUTO
, panic_on_cscount
, CTLFLAG_RW
, &panic_on_cscount
, 0,
113 "Panic if attempting to switch lwkt's while mastering cpusync");
115 SYSCTL_QUAD(_lwkt
, OID_AUTO
, switch_count
, CTLFLAG_RW
, &switch_count
, 0,
116 "Number of switched threads");
117 SYSCTL_QUAD(_lwkt
, OID_AUTO
, preempt_hit
, CTLFLAG_RW
, &preempt_hit
, 0,
118 "Successful preemption events");
119 SYSCTL_QUAD(_lwkt
, OID_AUTO
, preempt_miss
, CTLFLAG_RW
, &preempt_miss
, 0,
120 "Failed preemption events");
121 SYSCTL_QUAD(_lwkt
, OID_AUTO
, preempt_weird
, CTLFLAG_RW
, &preempt_weird
, 0,
122 "Number of preempted threads.");
123 static int fairq_enable
= 0;
124 SYSCTL_INT(_lwkt
, OID_AUTO
, fairq_enable
, CTLFLAG_RW
,
125 &fairq_enable
, 0, "Turn on fairq priority accumulators");
126 static int fairq_bypass
= -1;
127 SYSCTL_INT(_lwkt
, OID_AUTO
, fairq_bypass
, CTLFLAG_RW
,
128 &fairq_bypass
, 0, "Allow fairq to bypass td on token failure");
129 extern int lwkt_sched_debug
;
130 int lwkt_sched_debug
= 0;
131 SYSCTL_INT(_lwkt
, OID_AUTO
, sched_debug
, CTLFLAG_RW
,
132 &lwkt_sched_debug
, 0, "Scheduler debug");
133 static u_int lwkt_spin_loops
= 10;
134 SYSCTL_UINT(_lwkt
, OID_AUTO
, spin_loops
, CTLFLAG_RW
,
135 &lwkt_spin_loops
, 0, "Scheduler spin loops until sorted decon");
136 static int preempt_enable
= 1;
137 SYSCTL_INT(_lwkt
, OID_AUTO
, preempt_enable
, CTLFLAG_RW
,
138 &preempt_enable
, 0, "Enable preemption");
139 static int lwkt_cache_threads
= 0;
140 SYSCTL_INT(_lwkt
, OID_AUTO
, cache_threads
, CTLFLAG_RD
,
141 &lwkt_cache_threads
, 0, "thread+kstack cache");
144 * These helper procedures handle the runq, they can only be called from
145 * within a critical section.
147 * WARNING! Prior to SMP being brought up it is possible to enqueue and
148 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
149 * instead of 'mycpu' when referencing the globaldata structure. Once
150 * SMP live enqueuing and dequeueing only occurs on the current cpu.
154 _lwkt_dequeue(thread_t td
)
156 if (td
->td_flags
& TDF_RUNQ
) {
157 struct globaldata
*gd
= td
->td_gd
;
159 td
->td_flags
&= ~TDF_RUNQ
;
160 TAILQ_REMOVE(&gd
->gd_tdrunq
, td
, td_threadq
);
161 --gd
->gd_tdrunqcount
;
162 if (TAILQ_FIRST(&gd
->gd_tdrunq
) == NULL
)
163 atomic_clear_int(&gd
->gd_reqflags
, RQF_RUNNING
);
170 * There are a limited number of lwkt threads runnable since user
171 * processes only schedule one at a time per cpu. However, there can
172 * be many user processes in kernel mode exiting from a tsleep() which
175 * We scan the queue in both directions to help deal with degenerate
176 * situations when hundreds or thousands (or more) threads are runnable.
178 * NOTE: lwkt_schedulerclock() will force a round-robin based on td_pri and
179 * will ignore user priority. This is to ensure that user threads in
180 * kernel mode get cpu at some point regardless of what the user
185 _lwkt_enqueue(thread_t td
)
187 thread_t xtd
; /* forward scan */
188 thread_t rtd
; /* reverse scan */
190 if ((td
->td_flags
& (TDF_RUNQ
|TDF_MIGRATING
|TDF_BLOCKQ
)) == 0) {
191 struct globaldata
*gd
= td
->td_gd
;
193 td
->td_flags
|= TDF_RUNQ
;
194 xtd
= TAILQ_FIRST(&gd
->gd_tdrunq
);
196 TAILQ_INSERT_TAIL(&gd
->gd_tdrunq
, td
, td_threadq
);
197 atomic_set_int(&gd
->gd_reqflags
, RQF_RUNNING
);
200 * NOTE: td_upri - higher numbers more desireable, same sense
201 * as td_pri (typically reversed from lwp_upri).
203 * In the equal priority case we want the best selection
204 * at the beginning so the less desireable selections know
205 * that they have to setrunqueue/go-to-another-cpu, even
206 * though it means switching back to the 'best' selection.
207 * This also avoids degenerate situations when many threads
208 * are runnable or waking up at the same time.
210 * If upri matches exactly place at end/round-robin.
212 rtd
= TAILQ_LAST(&gd
->gd_tdrunq
, lwkt_queue
);
215 (xtd
->td_pri
> td
->td_pri
||
216 (xtd
->td_pri
== td
->td_pri
&&
217 xtd
->td_upri
>= td
->td_upri
))) {
218 xtd
= TAILQ_NEXT(xtd
, td_threadq
);
221 * Doing a reverse scan at the same time is an optimization
222 * for the insert-closer-to-tail case that avoids having to
223 * scan the entire list. This situation can occur when
224 * thousands of threads are woken up at the same time.
226 if (rtd
->td_pri
> td
->td_pri
||
227 (rtd
->td_pri
== td
->td_pri
&&
228 rtd
->td_upri
>= td
->td_upri
)) {
229 TAILQ_INSERT_AFTER(&gd
->gd_tdrunq
, rtd
, td
, td_threadq
);
232 rtd
= TAILQ_PREV(rtd
, lwkt_queue
, td_threadq
);
235 TAILQ_INSERT_BEFORE(xtd
, td
, td_threadq
);
237 TAILQ_INSERT_TAIL(&gd
->gd_tdrunq
, td
, td_threadq
);
240 ++gd
->gd_tdrunqcount
;
243 * Request a LWKT reschedule if we are now at the head of the queue.
245 if (TAILQ_FIRST(&gd
->gd_tdrunq
) == td
)
251 _lwkt_thread_ctor(void *obj
, void *privdata
, int ocflags
)
253 struct thread
*td
= (struct thread
*)obj
;
255 td
->td_kstack
= NULL
;
256 td
->td_kstack_size
= 0;
257 td
->td_flags
= TDF_ALLOCATED_THREAD
;
263 _lwkt_thread_dtor(void *obj
, void *privdata
)
265 struct thread
*td
= (struct thread
*)obj
;
267 KASSERT(td
->td_flags
& TDF_ALLOCATED_THREAD
,
268 ("_lwkt_thread_dtor: not allocated from objcache"));
269 KASSERT((td
->td_flags
& TDF_ALLOCATED_STACK
) && td
->td_kstack
&&
270 td
->td_kstack_size
> 0,
271 ("_lwkt_thread_dtor: corrupted stack"));
272 kmem_free(&kernel_map
, (vm_offset_t
)td
->td_kstack
, td
->td_kstack_size
);
273 td
->td_kstack
= NULL
;
278 * Initialize the lwkt s/system.
280 * Nominally cache up to 32 thread + kstack structures. Cache more on
281 * systems with a lot of cpu cores.
286 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads
);
287 if (lwkt_cache_threads
== 0) {
288 lwkt_cache_threads
= ncpus
* 4;
289 if (lwkt_cache_threads
< 32)
290 lwkt_cache_threads
= 32;
292 thread_cache
= objcache_create_mbacked(
293 M_THREAD
, sizeof(struct thread
),
294 0, lwkt_cache_threads
,
295 _lwkt_thread_ctor
, _lwkt_thread_dtor
, NULL
);
297 SYSINIT(lwkt_init
, SI_BOOT2_LWKT_INIT
, SI_ORDER_FIRST
, lwkt_init
, NULL
);
300 * Schedule a thread to run. As the current thread we can always safely
301 * schedule ourselves, and a shortcut procedure is provided for that
304 * (non-blocking, self contained on a per cpu basis)
307 lwkt_schedule_self(thread_t td
)
309 KKASSERT((td
->td_flags
& TDF_MIGRATING
) == 0);
310 crit_enter_quick(td
);
311 KASSERT(td
!= &td
->td_gd
->gd_idlethread
,
312 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
313 KKASSERT(td
->td_lwp
== NULL
||
314 (td
->td_lwp
->lwp_mpflags
& LWP_MP_ONRUNQ
) == 0);
320 * Deschedule a thread.
322 * (non-blocking, self contained on a per cpu basis)
325 lwkt_deschedule_self(thread_t td
)
327 crit_enter_quick(td
);
333 * LWKTs operate on a per-cpu basis
335 * WARNING! Called from early boot, 'mycpu' may not work yet.
338 lwkt_gdinit(struct globaldata
*gd
)
340 TAILQ_INIT(&gd
->gd_tdrunq
);
341 TAILQ_INIT(&gd
->gd_tdallq
);
345 * Create a new thread. The thread must be associated with a process context
346 * or LWKT start address before it can be scheduled. If the target cpu is
347 * -1 the thread will be created on the current cpu.
349 * If you intend to create a thread without a process context this function
350 * does everything except load the startup and switcher function.
353 lwkt_alloc_thread(struct thread
*td
, int stksize
, int cpu
, int flags
)
355 static int cpu_rotator
;
356 globaldata_t gd
= mycpu
;
360 * If static thread storage is not supplied allocate a thread. Reuse
361 * a cached free thread if possible. gd_freetd is used to keep an exiting
362 * thread intact through the exit.
366 if ((td
= gd
->gd_freetd
) != NULL
) {
367 KKASSERT((td
->td_flags
& (TDF_RUNNING
|TDF_PREEMPT_LOCK
|
369 gd
->gd_freetd
= NULL
;
371 td
= objcache_get(thread_cache
, M_WAITOK
);
372 KKASSERT((td
->td_flags
& (TDF_RUNNING
|TDF_PREEMPT_LOCK
|
376 KASSERT((td
->td_flags
&
377 (TDF_ALLOCATED_THREAD
|TDF_RUNNING
|TDF_PREEMPT_LOCK
)) ==
378 TDF_ALLOCATED_THREAD
,
379 ("lwkt_alloc_thread: corrupted td flags 0x%X", td
->td_flags
));
380 flags
|= td
->td_flags
& (TDF_ALLOCATED_THREAD
|TDF_ALLOCATED_STACK
);
384 * Try to reuse cached stack.
386 if ((stack
= td
->td_kstack
) != NULL
&& td
->td_kstack_size
!= stksize
) {
387 if (flags
& TDF_ALLOCATED_STACK
) {
388 kmem_free(&kernel_map
, (vm_offset_t
)stack
, td
->td_kstack_size
);
394 stack
= (void *)kmem_alloc_stack(&kernel_map
, stksize
, 0);
396 stack
= (void *)kmem_alloc_stack(&kernel_map
, stksize
,
398 flags
|= TDF_ALLOCATED_STACK
;
405 lwkt_init_thread(td
, stack
, stksize
, flags
, globaldata_find(cpu
));
410 * Initialize a preexisting thread structure. This function is used by
411 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
413 * All threads start out in a critical section at a priority of
414 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
415 * appropriate. This function may send an IPI message when the
416 * requested cpu is not the current cpu and consequently gd_tdallq may
417 * not be initialized synchronously from the point of view of the originating
420 * NOTE! we have to be careful in regards to creating threads for other cpus
421 * if SMP has not yet been activated.
424 lwkt_init_thread_remote(void *arg
)
429 * Protected by critical section held by IPI dispatch
431 TAILQ_INSERT_TAIL(&td
->td_gd
->gd_tdallq
, td
, td_allq
);
435 * lwkt core thread structural initialization.
437 * NOTE: All threads are initialized as mpsafe threads.
440 lwkt_init_thread(thread_t td
, void *stack
, int stksize
, int flags
,
441 struct globaldata
*gd
)
443 globaldata_t mygd
= mycpu
;
445 bzero(td
, sizeof(struct thread
));
446 td
->td_kstack
= stack
;
447 td
->td_kstack_size
= stksize
;
448 td
->td_flags
= flags
;
450 td
->td_type
= TD_TYPE_GENERIC
;
452 td
->td_pri
= TDPRI_KERN_DAEMON
;
453 td
->td_critcount
= 1;
454 td
->td_toks_have
= NULL
;
455 td
->td_toks_stop
= &td
->td_toks_base
;
456 if (lwkt_use_spin_port
|| (flags
& TDF_FORCE_SPINPORT
)) {
457 lwkt_initport_spin(&td
->td_msgport
, td
,
458 (flags
& TDF_FIXEDCPU
) ? TRUE
: FALSE
);
460 lwkt_initport_thread(&td
->td_msgport
, td
);
462 pmap_init_thread(td
);
464 * Normally initializing a thread for a remote cpu requires sending an
465 * IPI. However, the idlethread is setup before the other cpus are
466 * activated so we have to treat it as a special case. XXX manipulation
467 * of gd_tdallq requires the BGL.
469 if (gd
== mygd
|| td
== &gd
->gd_idlethread
) {
471 TAILQ_INSERT_TAIL(&gd
->gd_tdallq
, td
, td_allq
);
474 lwkt_send_ipiq(gd
, lwkt_init_thread_remote
, td
);
476 dsched_enter_thread(td
);
480 lwkt_set_comm(thread_t td
, const char *ctl
, ...)
485 kvsnprintf(td
->td_comm
, sizeof(td
->td_comm
), ctl
, va
);
487 KTR_LOG(ctxsw_newtd
, td
, td
->td_comm
);
491 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE
492 * this does not prevent the thread from migrating to another cpu so the
493 * gd_tdallq state is not protected by this.
496 lwkt_hold(thread_t td
)
498 atomic_add_int(&td
->td_refs
, 1);
502 lwkt_rele(thread_t td
)
504 KKASSERT(td
->td_refs
> 0);
505 atomic_add_int(&td
->td_refs
, -1);
509 lwkt_free_thread(thread_t td
)
511 KKASSERT(td
->td_refs
== 0);
512 KKASSERT((td
->td_flags
& (TDF_RUNNING
| TDF_PREEMPT_LOCK
|
513 TDF_RUNQ
| TDF_TSLEEPQ
)) == 0);
514 if (td
->td_flags
& TDF_ALLOCATED_THREAD
) {
515 objcache_put(thread_cache
, td
);
516 } else if (td
->td_flags
& TDF_ALLOCATED_STACK
) {
517 /* client-allocated struct with internally allocated stack */
518 KASSERT(td
->td_kstack
&& td
->td_kstack_size
> 0,
519 ("lwkt_free_thread: corrupted stack"));
520 kmem_free(&kernel_map
, (vm_offset_t
)td
->td_kstack
, td
->td_kstack_size
);
521 td
->td_kstack
= NULL
;
522 td
->td_kstack_size
= 0;
525 KTR_LOG(ctxsw_deadtd
, td
);
530 * Switch to the next runnable lwkt. If no LWKTs are runnable then
531 * switch to the idlethread. Switching must occur within a critical
532 * section to avoid races with the scheduling queue.
534 * We always have full control over our cpu's run queue. Other cpus
535 * that wish to manipulate our queue must use the cpu_*msg() calls to
536 * talk to our cpu, so a critical section is all that is needed and
537 * the result is very, very fast thread switching.
539 * The LWKT scheduler uses a fixed priority model and round-robins at
540 * each priority level. User process scheduling is a totally
541 * different beast and LWKT priorities should not be confused with
542 * user process priorities.
544 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
545 * is not called by the current thread in the preemption case, only when
546 * the preempting thread blocks (in order to return to the original thread).
548 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread
549 * migration and tsleep deschedule the current lwkt thread and call
550 * lwkt_switch(). In particular, the target cpu of the migration fully
551 * expects the thread to become non-runnable and can deadlock against
552 * cpusync operations if we run any IPIs prior to switching the thread out.
554 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF
555 * THE CURRENT THREAD HAS BEEN DESCHEDULED!
560 globaldata_t gd
= mycpu
;
561 thread_t td
= gd
->gd_curthread
;
565 uint64_t tsc_base
= rdtsc();
568 KKASSERT(gd
->gd_processing_ipiq
== 0);
569 KKASSERT(td
->td_flags
& TDF_RUNNING
);
572 * Switching from within a 'fast' (non thread switched) interrupt or IPI
573 * is illegal. However, we may have to do it anyway if we hit a fatal
574 * kernel trap or we have paniced.
576 * If this case occurs save and restore the interrupt nesting level.
578 if (gd
->gd_intr_nesting_level
) {
582 if (gd
->gd_trap_nesting_level
== 0 && panic_cpu_gd
!= mycpu
) {
583 panic("lwkt_switch: Attempt to switch from a "
584 "fast interrupt, ipi, or hard code section, "
588 savegdnest
= gd
->gd_intr_nesting_level
;
589 savegdtrap
= gd
->gd_trap_nesting_level
;
590 gd
->gd_intr_nesting_level
= 0;
591 gd
->gd_trap_nesting_level
= 0;
592 if ((td
->td_flags
& TDF_PANICWARN
) == 0) {
593 td
->td_flags
|= TDF_PANICWARN
;
594 kprintf("Warning: thread switch from interrupt, IPI, "
595 "or hard code section.\n"
596 "thread %p (%s)\n", td
, td
->td_comm
);
600 gd
->gd_intr_nesting_level
= savegdnest
;
601 gd
->gd_trap_nesting_level
= savegdtrap
;
607 * Release our current user process designation if we are blocking
608 * or if a user reschedule was requested.
610 * NOTE: This function is NOT called if we are switching into or
611 * returning from a preemption.
613 * NOTE: Releasing our current user process designation may cause
614 * it to be assigned to another thread, which in turn will
615 * cause us to block in the usched acquire code when we attempt
616 * to return to userland.
618 * NOTE: On SMP systems this can be very nasty when heavy token
619 * contention is present so we want to be careful not to
620 * release the designation gratuitously.
622 if (td
->td_release
&&
623 (user_resched_wanted() || (td
->td_flags
& TDF_RUNQ
) == 0)) {
628 * Release all tokens. Once we do this we must remain in the critical
629 * section and cannot run IPIs or other interrupts until we switch away
630 * because they may implode if they try to get a token using our thread
634 if (TD_TOKS_HELD(td
))
635 lwkt_relalltokens(td
);
638 * We had better not be holding any spin locks, but don't get into an
639 * endless panic loop.
641 KASSERT(gd
->gd_spinlocks
== 0 || panicstr
!= NULL
,
642 ("lwkt_switch: still holding %d exclusive spinlocks!",
646 if (td
->td_cscount
) {
647 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
649 if (panic_on_cscount
)
650 panic("switching while mastering cpusync");
655 * If we had preempted another thread on this cpu, resume the preempted
656 * thread. This occurs transparently, whether the preempted thread
657 * was scheduled or not (it may have been preempted after descheduling
660 * We have to setup the MP lock for the original thread after backing
661 * out the adjustment that was made to curthread when the original
664 if ((ntd
= td
->td_preempted
) != NULL
) {
665 KKASSERT(ntd
->td_flags
& TDF_PREEMPT_LOCK
);
666 ntd
->td_flags
|= TDF_PREEMPT_DONE
;
667 ntd
->td_contended
= 0; /* reset contended */
670 * The interrupt may have woken a thread up, we need to properly
671 * set the reschedule flag if the originally interrupted thread is
672 * at a lower priority.
674 * The interrupt may not have descheduled.
676 if (TAILQ_FIRST(&gd
->gd_tdrunq
) != ntd
)
678 goto havethread_preempted
;
682 * Figure out switch target. If we cannot switch to our desired target
683 * look for a thread that we can switch to.
685 * NOTE! The limited spin loop and related parameters are extremely
686 * important for system performance, particularly for pipes and
687 * concurrent conflicting VM faults.
689 clear_lwkt_resched();
690 ntd
= TAILQ_FIRST(&gd
->gd_tdrunq
);
694 if (TD_TOKS_NOT_HELD(ntd
) ||
695 lwkt_getalltokens(ntd
, (ntd
->td_contended
> lwkt_spin_loops
)))
699 ++gd
->gd_cnt
.v_lock_colls
;
700 ++ntd
->td_contended
; /* overflow ok */
702 if (tsc_frequency
&& rdtsc() - tsc_base
> tsc_frequency
) {
703 kprintf("lwkt_switch: excessive contended %d "
704 "thread %p\n", ntd
->td_contended
, ntd
);
708 } while (ntd
->td_contended
< (lwkt_spin_loops
>> 1));
712 * Bleh, the thread we wanted to switch to has a contended token.
713 * See if we can switch to another thread.
715 * We generally don't want to do this because it represents a
716 * priority inversion. Do not allow the case if the thread
717 * is returning to userland (not a kernel thread) AND the thread
720 while ((ntd
= TAILQ_NEXT(ntd
, td_threadq
)) != NULL
) {
721 if (ntd
->td_pri
< TDPRI_KERN_LPSCHED
&& upri
> ntd
->td_upri
)
728 if (TD_TOKS_NOT_HELD(ntd
) ||
729 lwkt_getalltokens(ntd
, (ntd
->td_contended
> lwkt_spin_loops
))) {
732 ++ntd
->td_contended
; /* overflow ok */
733 ++gd
->gd_cnt
.v_lock_colls
;
737 * Fall through, switch to idle thread to get us out of the current
738 * context. Since we were contended, prevent HLT by flagging a
745 * We either contended on ntd or the runq is empty. We must switch
746 * through the idle thread to get out of the current context.
748 ntd
= &gd
->gd_idlethread
;
749 if (gd
->gd_trap_nesting_level
== 0 && panicstr
== NULL
)
750 ASSERT_NO_TOKENS_HELD(ntd
);
751 cpu_time
.cp_msg
[0] = 0;
756 * Clear gd_idle_repeat when doing a normal switch to a non-idle
759 ntd
->td_wmesg
= NULL
;
760 ntd
->td_contended
= 0; /* reset once scheduled */
761 ++gd
->gd_cnt
.v_swtch
;
762 gd
->gd_idle_repeat
= 0;
764 havethread_preempted
:
766 * If the new target does not need the MP lock and we are holding it,
767 * release the MP lock. If the new target requires the MP lock we have
768 * already acquired it for the target.
772 KASSERT(ntd
->td_critcount
,
773 ("priority problem in lwkt_switch %d %d",
774 td
->td_critcount
, ntd
->td_critcount
));
778 * Execute the actual thread switch operation. This function
779 * returns to the current thread and returns the previous thread
780 * (which may be different from the thread we switched to).
782 * We are responsible for marking ntd as TDF_RUNNING.
784 KKASSERT((ntd
->td_flags
& TDF_RUNNING
) == 0);
786 KTR_LOG(ctxsw_sw
, gd
->gd_cpuid
, ntd
);
787 ntd
->td_flags
|= TDF_RUNNING
;
788 lwkt_switch_return(td
->td_switch(ntd
));
789 /* ntd invalid, td_switch() can return a different thread_t */
793 * catch-all. XXX is this strictly needed?
797 /* NOTE: current cpu may have changed after switch */
802 * Called by assembly in the td_switch (thread restore path) for thread
803 * bootstrap cases which do not 'return' to lwkt_switch().
806 lwkt_switch_return(thread_t otd
)
810 uint64_t tsc_base
= rdtsc();
814 exiting
= otd
->td_flags
& TDF_EXITING
;
818 * Check if otd was migrating. Now that we are on ntd we can finish
819 * up the migration. This is a bit messy but it is the only place
820 * where td is known to be fully descheduled.
822 * We can only activate the migration if otd was migrating but not
823 * held on the cpu due to a preemption chain. We still have to
824 * clear TDF_RUNNING on the old thread either way.
826 * We are responsible for clearing the previously running thread's
829 if ((rgd
= otd
->td_migrate_gd
) != NULL
&&
830 (otd
->td_flags
& TDF_PREEMPT_LOCK
) == 0) {
831 KKASSERT((otd
->td_flags
& (TDF_MIGRATING
| TDF_RUNNING
)) ==
832 (TDF_MIGRATING
| TDF_RUNNING
));
833 otd
->td_migrate_gd
= NULL
;
834 otd
->td_flags
&= ~TDF_RUNNING
;
835 lwkt_send_ipiq(rgd
, lwkt_setcpu_remote
, otd
);
837 otd
->td_flags
&= ~TDF_RUNNING
;
841 * Final exit validations (see lwp_wait()). Note that otd becomes
842 * invalid the *instant* we set TDF_MP_EXITSIG.
844 * Use the EXITING status loaded from before we clear TDF_RUNNING,
845 * because if it is not set otd becomes invalid the instant we clear
846 * TDF_RUNNING on it (otherwise, if the system is fast enough, we
847 * might 'steal' TDF_EXITING from another switch-return!).
852 mpflags
= otd
->td_mpflags
;
855 if (mpflags
& TDF_MP_EXITWAIT
) {
856 if (atomic_cmpset_int(&otd
->td_mpflags
, mpflags
,
857 mpflags
| TDF_MP_EXITSIG
)) {
862 if (atomic_cmpset_int(&otd
->td_mpflags
, mpflags
,
863 mpflags
| TDF_MP_EXITSIG
)) {
870 if (tsc_frequency
&& rdtsc() - tsc_base
> tsc_frequency
) {
871 kprintf("lwkt_switch_return: excessive TDF_EXITING "
880 * Request that the target thread preempt the current thread. Preemption
881 * can only occur only:
883 * - If our critical section is the one that we were called with
884 * - The relative priority of the target thread is higher
885 * - The target is not excessively interrupt-nested via td_nest_count
886 * - The target thread holds no tokens.
887 * - The target thread is not already scheduled and belongs to the
889 * - The current thread is not holding any spin-locks.
891 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
892 * this is called via lwkt_schedule() through the td_preemptable callback.
893 * critcount is the managed critical priority that we should ignore in order
894 * to determine whether preemption is possible (aka usually just the crit
895 * priority of lwkt_schedule() itself).
897 * Preemption is typically limited to interrupt threads.
899 * Operation works in a fairly straight-forward manner. The normal
900 * scheduling code is bypassed and we switch directly to the target
901 * thread. When the target thread attempts to block or switch away
902 * code at the base of lwkt_switch() will switch directly back to our
903 * thread. Our thread is able to retain whatever tokens it holds and
904 * if the target needs one of them the target will switch back to us
905 * and reschedule itself normally.
908 lwkt_preempt(thread_t ntd
, int critcount
)
910 struct globaldata
*gd
= mycpu
;
913 int save_gd_intr_nesting_level
;
916 * The caller has put us in a critical section. We can only preempt
917 * if the caller of the caller was not in a critical section (basically
918 * a local interrupt), as determined by the 'critcount' parameter. We
919 * also can't preempt if the caller is holding any spinlocks (even if
920 * he isn't in a critical section). This also handles the tokens test.
922 * YYY The target thread must be in a critical section (else it must
923 * inherit our critical section? I dunno yet).
925 KASSERT(ntd
->td_critcount
, ("BADCRIT0 %d", ntd
->td_pri
));
927 td
= gd
->gd_curthread
;
928 if (preempt_enable
== 0) {
932 if (ntd
->td_pri
<= td
->td_pri
) {
936 if (td
->td_critcount
> critcount
) {
940 if (td
->td_nest_count
>= 2) {
944 if (td
->td_cscount
) {
948 if (ntd
->td_gd
!= gd
) {
954 * We don't have to check spinlocks here as they will also bump
957 * Do not try to preempt if the target thread is holding any tokens.
958 * We could try to acquire the tokens but this case is so rare there
959 * is no need to support it.
961 KKASSERT(gd
->gd_spinlocks
== 0);
963 if (TD_TOKS_HELD(ntd
)) {
967 if (td
== ntd
|| ((td
->td_flags
| ntd
->td_flags
) & TDF_PREEMPT_LOCK
)) {
971 if (ntd
->td_preempted
) {
975 KKASSERT(gd
->gd_processing_ipiq
== 0);
978 * Since we are able to preempt the current thread, there is no need to
979 * call need_lwkt_resched().
981 * We must temporarily clear gd_intr_nesting_level around the switch
982 * since switchouts from the target thread are allowed (they will just
983 * return to our thread), and since the target thread has its own stack.
985 * A preemption must switch back to the original thread, assert the
989 ntd
->td_preempted
= td
;
990 td
->td_flags
|= TDF_PREEMPT_LOCK
;
991 KTR_LOG(ctxsw_pre
, gd
->gd_cpuid
, ntd
);
992 save_gd_intr_nesting_level
= gd
->gd_intr_nesting_level
;
993 gd
->gd_intr_nesting_level
= 0;
995 KKASSERT((ntd
->td_flags
& TDF_RUNNING
) == 0);
996 ntd
->td_flags
|= TDF_RUNNING
;
997 xtd
= td
->td_switch(ntd
);
998 KKASSERT(xtd
== ntd
);
999 lwkt_switch_return(xtd
);
1000 gd
->gd_intr_nesting_level
= save_gd_intr_nesting_level
;
1002 KKASSERT(ntd
->td_preempted
&& (td
->td_flags
& TDF_PREEMPT_DONE
));
1003 ntd
->td_preempted
= NULL
;
1004 td
->td_flags
&= ~(TDF_PREEMPT_LOCK
|TDF_PREEMPT_DONE
);
1008 * Conditionally call splz() if gd_reqflags indicates work is pending.
1009 * This will work inside a critical section but not inside a hard code
1012 * (self contained on a per cpu basis)
1017 globaldata_t gd
= mycpu
;
1018 thread_t td
= gd
->gd_curthread
;
1020 if ((gd
->gd_reqflags
& RQF_IDLECHECK_MASK
) &&
1021 gd
->gd_intr_nesting_level
== 0 &&
1022 td
->td_nest_count
< 2)
1029 * This version is integrated into crit_exit, reqflags has already
1030 * been tested but td_critcount has not.
1032 * We only want to execute the splz() on the 1->0 transition of
1033 * critcount and not in a hard code section or if too deeply nested.
1035 * NOTE: gd->gd_spinlocks is implied to be 0 when td_critcount is 0.
1038 lwkt_maybe_splz(thread_t td
)
1040 globaldata_t gd
= td
->td_gd
;
1042 if (td
->td_critcount
== 0 &&
1043 gd
->gd_intr_nesting_level
== 0 &&
1044 td
->td_nest_count
< 2)
1051 * Drivers which set up processing co-threads can call this function to
1052 * run the co-thread at a higher priority and to allow it to preempt
1056 lwkt_set_interrupt_support_thread(void)
1058 thread_t td
= curthread
;
1060 lwkt_setpri_self(TDPRI_INT_SUPPORT
);
1061 td
->td_flags
|= TDF_INTTHREAD
;
1062 td
->td_preemptable
= lwkt_preempt
;
1067 * This function is used to negotiate a passive release of the current
1068 * process/lwp designation with the user scheduler, allowing the user
1069 * scheduler to schedule another user thread. The related kernel thread
1070 * (curthread) continues running in the released state.
1073 lwkt_passive_release(struct thread
*td
)
1075 struct lwp
*lp
= td
->td_lwp
;
1077 td
->td_release
= NULL
;
1078 lwkt_setpri_self(TDPRI_KERN_USER
);
1080 lp
->lwp_proc
->p_usched
->release_curproc(lp
);
1085 * This implements a LWKT yield, allowing a kernel thread to yield to other
1086 * kernel threads at the same or higher priority. This function can be
1087 * called in a tight loop and will typically only yield once per tick.
1089 * Most kernel threads run at the same priority in order to allow equal
1092 * (self contained on a per cpu basis)
1097 globaldata_t gd
= mycpu
;
1098 thread_t td
= gd
->gd_curthread
;
1101 * Should never be called with spinlocks held but there is a path
1102 * via ACPI where it might happen.
1104 if (gd
->gd_spinlocks
)
1108 * Safe to call splz if we are not too-heavily nested.
1110 if ((gd
->gd_reqflags
& RQF_IDLECHECK_MASK
) && td
->td_nest_count
< 2)
1114 * Caller allows switching
1116 if (lwkt_resched_wanted()) {
1117 lwkt_schedule_self(curthread
);
1123 * The quick version processes pending interrupts and higher-priority
1124 * LWKT threads but will not round-robin same-priority LWKT threads.
1126 * When called while attempting to return to userland the only same-pri
1127 * threads are the ones which have already tried to become the current
1131 lwkt_yield_quick(void)
1133 globaldata_t gd
= mycpu
;
1134 thread_t td
= gd
->gd_curthread
;
1136 if ((gd
->gd_reqflags
& RQF_IDLECHECK_MASK
) && td
->td_nest_count
< 2)
1138 if (lwkt_resched_wanted()) {
1140 if (TAILQ_FIRST(&gd
->gd_tdrunq
) == td
) {
1141 clear_lwkt_resched();
1143 lwkt_schedule_self(curthread
);
1151 * This yield is designed for kernel threads with a user context.
1153 * The kernel acting on behalf of the user is potentially cpu-bound,
1154 * this function will efficiently allow other threads to run and also
1155 * switch to other processes by releasing.
1157 * The lwkt_user_yield() function is designed to have very low overhead
1158 * if no yield is determined to be needed.
1161 lwkt_user_yield(void)
1163 globaldata_t gd
= mycpu
;
1164 thread_t td
= gd
->gd_curthread
;
1167 * Should never be called with spinlocks held but there is a path
1168 * via ACPI where it might happen.
1170 if (gd
->gd_spinlocks
)
1174 * Always run any pending interrupts in case we are in a critical
1177 if ((gd
->gd_reqflags
& RQF_IDLECHECK_MASK
) && td
->td_nest_count
< 2)
1181 * Switch (which forces a release) if another kernel thread needs
1182 * the cpu, if userland wants us to resched, or if our kernel
1183 * quantum has run out.
1185 if (lwkt_resched_wanted() ||
1186 user_resched_wanted())
1193 * Reacquire the current process if we are released.
1195 * XXX not implemented atm. The kernel may be holding locks and such,
1196 * so we want the thread to continue to receive cpu.
1198 if (td
->td_release
== NULL
&& lp
) {
1199 lp
->lwp_proc
->p_usched
->acquire_curproc(lp
);
1200 td
->td_release
= lwkt_passive_release
;
1201 lwkt_setpri_self(TDPRI_USER_NORM
);
1207 * Generic schedule. Possibly schedule threads belonging to other cpus and
1208 * deal with threads that might be blocked on a wait queue.
1210 * We have a little helper inline function which does additional work after
1211 * the thread has been enqueued, including dealing with preemption and
1212 * setting need_lwkt_resched() (which prevents the kernel from returning
1213 * to userland until it has processed higher priority threads).
1215 * It is possible for this routine to be called after a failed _enqueue
1216 * (due to the target thread migrating, sleeping, or otherwise blocked).
1217 * We have to check that the thread is actually on the run queue!
1221 _lwkt_schedule_post(globaldata_t gd
, thread_t ntd
, int ccount
)
1223 if (ntd
->td_flags
& TDF_RUNQ
) {
1224 if (ntd
->td_preemptable
) {
1225 ntd
->td_preemptable(ntd
, ccount
); /* YYY +token */
1232 _lwkt_schedule(thread_t td
)
1234 globaldata_t mygd
= mycpu
;
1236 KASSERT(td
!= &td
->td_gd
->gd_idlethread
,
1237 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
1238 KKASSERT((td
->td_flags
& TDF_MIGRATING
) == 0);
1239 crit_enter_gd(mygd
);
1240 KKASSERT(td
->td_lwp
== NULL
||
1241 (td
->td_lwp
->lwp_mpflags
& LWP_MP_ONRUNQ
) == 0);
1243 if (td
== mygd
->gd_curthread
) {
1247 * If we own the thread, there is no race (since we are in a
1248 * critical section). If we do not own the thread there might
1249 * be a race but the target cpu will deal with it.
1251 if (td
->td_gd
== mygd
) {
1253 _lwkt_schedule_post(mygd
, td
, 1);
1255 lwkt_send_ipiq3(td
->td_gd
, lwkt_schedule_remote
, td
, 0);
1262 lwkt_schedule(thread_t td
)
1268 lwkt_schedule_noresched(thread_t td
) /* XXX not impl */
1274 * When scheduled remotely if frame != NULL the IPIQ is being
1275 * run via doreti or an interrupt then preemption can be allowed.
1277 * To allow preemption we have to drop the critical section so only
1278 * one is present in _lwkt_schedule_post.
1281 lwkt_schedule_remote(void *arg
, int arg2
, struct intrframe
*frame
)
1283 thread_t td
= curthread
;
1286 if (frame
&& ntd
->td_preemptable
) {
1287 crit_exit_noyield(td
);
1288 _lwkt_schedule(ntd
);
1289 crit_enter_quick(td
);
1291 _lwkt_schedule(ntd
);
1296 * Thread migration using a 'Pull' method. The thread may or may not be
1297 * the current thread. It MUST be descheduled and in a stable state.
1298 * lwkt_giveaway() must be called on the cpu owning the thread.
1300 * At any point after lwkt_giveaway() is called, the target cpu may
1301 * 'pull' the thread by calling lwkt_acquire().
1303 * We have to make sure the thread is not sitting on a per-cpu tsleep
1304 * queue or it will blow up when it moves to another cpu.
1306 * MPSAFE - must be called under very specific conditions.
1309 lwkt_giveaway(thread_t td
)
1311 globaldata_t gd
= mycpu
;
1314 if (td
->td_flags
& TDF_TSLEEPQ
)
1316 KKASSERT(td
->td_gd
== gd
);
1317 TAILQ_REMOVE(&gd
->gd_tdallq
, td
, td_allq
);
1318 td
->td_flags
|= TDF_MIGRATING
;
1323 lwkt_acquire(thread_t td
)
1328 KKASSERT(td
->td_flags
& TDF_MIGRATING
);
1333 uint64_t tsc_base
= rdtsc();
1336 KKASSERT((td
->td_flags
& TDF_RUNQ
) == 0);
1337 crit_enter_gd(mygd
);
1338 DEBUG_PUSH_INFO("lwkt_acquire");
1339 while (td
->td_flags
& (TDF_RUNNING
|TDF_PREEMPT_LOCK
)) {
1340 lwkt_process_ipiq();
1342 #ifdef _KERNEL_VIRTUAL
1346 if (tsc_frequency
&& rdtsc() - tsc_base
> tsc_frequency
) {
1347 kprintf("lwkt_acquire: stuck td %p td->td_flags %08x\n",
1356 TAILQ_INSERT_TAIL(&mygd
->gd_tdallq
, td
, td_allq
);
1357 td
->td_flags
&= ~TDF_MIGRATING
;
1360 crit_enter_gd(mygd
);
1361 TAILQ_INSERT_TAIL(&mygd
->gd_tdallq
, td
, td_allq
);
1362 td
->td_flags
&= ~TDF_MIGRATING
;
1368 * Generic deschedule. Descheduling threads other then your own should be
1369 * done only in carefully controlled circumstances. Descheduling is
1372 * This function may block if the cpu has run out of messages.
1375 lwkt_deschedule(thread_t td
)
1378 if (td
== curthread
) {
1381 if (td
->td_gd
== mycpu
) {
1384 lwkt_send_ipiq(td
->td_gd
, (ipifunc1_t
)lwkt_deschedule
, td
);
1391 * Set the target thread's priority. This routine does not automatically
1392 * switch to a higher priority thread, LWKT threads are not designed for
1393 * continuous priority changes. Yield if you want to switch.
1396 lwkt_setpri(thread_t td
, int pri
)
1398 if (td
->td_pri
!= pri
) {
1401 if (td
->td_flags
& TDF_RUNQ
) {
1402 KKASSERT(td
->td_gd
== mycpu
);
1414 * Set the initial priority for a thread prior to it being scheduled for
1415 * the first time. The thread MUST NOT be scheduled before or during
1416 * this call. The thread may be assigned to a cpu other then the current
1419 * Typically used after a thread has been created with TDF_STOPPREQ,
1420 * and before the thread is initially scheduled.
1423 lwkt_setpri_initial(thread_t td
, int pri
)
1426 KKASSERT((td
->td_flags
& TDF_RUNQ
) == 0);
1431 lwkt_setpri_self(int pri
)
1433 thread_t td
= curthread
;
1435 KKASSERT(pri
>= 0 && pri
<= TDPRI_MAX
);
1437 if (td
->td_flags
& TDF_RUNQ
) {
1448 * hz tick scheduler clock for LWKT threads
1451 lwkt_schedulerclock(thread_t td
)
1453 globaldata_t gd
= td
->td_gd
;
1456 if (TAILQ_FIRST(&gd
->gd_tdrunq
) == td
) {
1458 * If the current thread is at the head of the runq shift it to the
1459 * end of any equal-priority threads and request a LWKT reschedule
1462 * Ignore upri in this situation. There will only be one user thread
1463 * in user mode, all others will be user threads running in kernel
1464 * mode and we have to make sure they get some cpu.
1466 xtd
= TAILQ_NEXT(td
, td_threadq
);
1467 if (xtd
&& xtd
->td_pri
== td
->td_pri
) {
1468 TAILQ_REMOVE(&gd
->gd_tdrunq
, td
, td_threadq
);
1469 while (xtd
&& xtd
->td_pri
== td
->td_pri
)
1470 xtd
= TAILQ_NEXT(xtd
, td_threadq
);
1472 TAILQ_INSERT_BEFORE(xtd
, td
, td_threadq
);
1474 TAILQ_INSERT_TAIL(&gd
->gd_tdrunq
, td
, td_threadq
);
1475 need_lwkt_resched();
1479 * If we scheduled a thread other than the one at the head of the
1480 * queue always request a reschedule every tick.
1482 need_lwkt_resched();
1487 * Migrate the current thread to the specified cpu.
1489 * This is accomplished by descheduling ourselves from the current cpu
1490 * and setting td_migrate_gd. The lwkt_switch() code will detect that the
1491 * 'old' thread wants to migrate after it has been completely switched out
1492 * and will complete the migration.
1494 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1496 * We must be sure to release our current process designation (if a user
1497 * process) before clearing out any tsleepq we are on because the release
1498 * code may re-add us.
1500 * We must be sure to remove ourselves from the current cpu's tsleepq
1501 * before potentially moving to another queue. The thread can be on
1502 * a tsleepq due to a left-over tsleep_interlock().
1506 lwkt_setcpu_self(globaldata_t rgd
)
1508 thread_t td
= curthread
;
1510 if (td
->td_gd
!= rgd
) {
1511 crit_enter_quick(td
);
1515 if (td
->td_flags
& TDF_TSLEEPQ
)
1519 * Set TDF_MIGRATING to prevent a spurious reschedule while we are
1520 * trying to deschedule ourselves and switch away, then deschedule
1521 * ourself, remove us from tdallq, and set td_migrate_gd. Finally,
1522 * call lwkt_switch() to complete the operation.
1524 td
->td_flags
|= TDF_MIGRATING
;
1525 lwkt_deschedule_self(td
);
1526 TAILQ_REMOVE(&td
->td_gd
->gd_tdallq
, td
, td_allq
);
1527 td
->td_migrate_gd
= rgd
;
1531 * We are now on the target cpu
1533 KKASSERT(rgd
== mycpu
);
1534 TAILQ_INSERT_TAIL(&rgd
->gd_tdallq
, td
, td_allq
);
1535 crit_exit_quick(td
);
1540 lwkt_migratecpu(int cpuid
)
1544 rgd
= globaldata_find(cpuid
);
1545 lwkt_setcpu_self(rgd
);
1549 * Remote IPI for cpu migration (called while in a critical section so we
1550 * do not have to enter another one).
1552 * The thread (td) has already been completely descheduled from the
1553 * originating cpu and we can simply assert the case. The thread is
1554 * assigned to the new cpu and enqueued.
1556 * The thread will re-add itself to tdallq when it resumes execution.
1559 lwkt_setcpu_remote(void *arg
)
1562 globaldata_t gd
= mycpu
;
1564 KKASSERT((td
->td_flags
& (TDF_RUNNING
|TDF_PREEMPT_LOCK
)) == 0);
1567 td
->td_flags
&= ~TDF_MIGRATING
;
1568 KKASSERT(td
->td_migrate_gd
== NULL
);
1569 KKASSERT(td
->td_lwp
== NULL
||
1570 (td
->td_lwp
->lwp_mpflags
& LWP_MP_ONRUNQ
) == 0);
1575 lwkt_preempted_proc(void)
1577 thread_t td
= curthread
;
1578 while (td
->td_preempted
)
1579 td
= td
->td_preempted
;
1584 * Create a kernel process/thread/whatever. It shares it's address space
1585 * with proc0 - ie: kernel only.
1587 * If the cpu is not specified one will be selected. In the future
1588 * specifying a cpu of -1 will enable kernel thread migration between
1592 lwkt_create(void (*func
)(void *), void *arg
, struct thread
**tdp
,
1593 thread_t
template, int tdflags
, int cpu
, const char *fmt
, ...)
1598 td
= lwkt_alloc_thread(template, LWKT_THREAD_STACK
, cpu
,
1602 cpu_set_thread_handler(td
, lwkt_exit
, func
, arg
);
1605 * Set up arg0 for 'ps' etc
1607 __va_start(ap
, fmt
);
1608 kvsnprintf(td
->td_comm
, sizeof(td
->td_comm
), fmt
, ap
);
1612 * Schedule the thread to run
1614 if (td
->td_flags
& TDF_NOSTART
)
1615 td
->td_flags
&= ~TDF_NOSTART
;
1622 * Destroy an LWKT thread. Warning! This function is not called when
1623 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1624 * uses a different reaping mechanism.
1629 thread_t td
= curthread
;
1634 * Do any cleanup that might block here
1636 if (td
->td_flags
& TDF_VERBOSE
)
1637 kprintf("kthread %p %s has exited\n", td
, td
->td_comm
);
1639 dsched_exit_thread(td
);
1642 * Get us into a critical section to interlock gd_freetd and loop
1643 * until we can get it freed.
1645 * We have to cache the current td in gd_freetd because objcache_put()ing
1646 * it would rip it out from under us while our thread is still active.
1648 * We are the current thread so of course our own TDF_RUNNING bit will
1649 * be set, so unlike the lwp reap code we don't wait for it to clear.
1652 crit_enter_quick(td
);
1655 tsleep(td
, 0, "tdreap", 1);
1658 if ((std
= gd
->gd_freetd
) != NULL
) {
1659 KKASSERT((std
->td_flags
& (TDF_RUNNING
|TDF_PREEMPT_LOCK
)) == 0);
1660 gd
->gd_freetd
= NULL
;
1661 objcache_put(thread_cache
, std
);
1668 * Remove thread resources from kernel lists and deschedule us for
1669 * the last time. We cannot block after this point or we may end
1670 * up with a stale td on the tsleepq.
1672 * None of this may block, the critical section is the only thing
1673 * protecting tdallq and the only thing preventing new lwkt_hold()
1676 if (td
->td_flags
& TDF_TSLEEPQ
)
1678 lwkt_deschedule_self(td
);
1679 lwkt_remove_tdallq(td
);
1680 KKASSERT(td
->td_refs
== 0);
1685 KKASSERT(gd
->gd_freetd
== NULL
);
1686 if (td
->td_flags
& TDF_ALLOCATED_THREAD
)
1692 lwkt_remove_tdallq(thread_t td
)
1694 KKASSERT(td
->td_gd
== mycpu
);
1695 TAILQ_REMOVE(&td
->td_gd
->gd_tdallq
, td
, td_allq
);
1699 * Code reduction and branch prediction improvements. Call/return
1700 * overhead on modern cpus often degenerates into 0 cycles due to
1701 * the cpu's branch prediction hardware and return pc cache. We
1702 * can take advantage of this by not inlining medium-complexity
1703 * functions and we can also reduce the branch prediction impact
1704 * by collapsing perfectly predictable branches into a single
1705 * procedure instead of duplicating it.
1707 * Is any of this noticeable? Probably not, so I'll take the
1708 * smaller code size.
1711 crit_exit_wrapper(__DEBUG_CRIT_ARG__
)
1713 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__
);
1719 thread_t td
= curthread
;
1720 int lcrit
= td
->td_critcount
;
1722 td
->td_critcount
= 0;
1723 panic("td_critcount is/would-go negative! %p %d", td
, lcrit
);
1728 * Called from debugger/panic on cpus which have been stopped. We must still
1729 * process the IPIQ while stopped.
1731 * If we are dumping also try to process any pending interrupts. This may
1732 * or may not work depending on the state of the cpu at the point it was
1736 lwkt_smp_stopped(void)
1738 globaldata_t gd
= mycpu
;
1741 lwkt_process_ipiq();
1742 --gd
->gd_intr_nesting_level
;
1744 ++gd
->gd_intr_nesting_level
;
1746 lwkt_process_ipiq();