2 * Copyright (c) 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>
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8 * modification, are permitted provided that the following conditions
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71 * From: @(#)kern_clock.c 8.5 (Berkeley) 1/21/94
72 * $FreeBSD: src/sys/kern/kern_timeout.c,v 1.59.2.1 2001/11/13 18:24:52 archie Exp $
75 * DRAGONFLY BGL STATUS
77 * All the API functions should be MP safe.
79 * The callback functions will be flagged as being MP safe if the
80 * timeout structure is initialized with callout_init_mp() instead of
83 * The helper threads cannot be made preempt-capable until after we
84 * clean up all the uses of splsoftclock() and related interlocks (which
85 * require the related functions to be MP safe as well).
88 * The callout mechanism is based on the work of Adam M. Costello and
89 * George Varghese, published in a technical report entitled "Redesigning
90 * the BSD Callout and Timer Facilities" and modified slightly for inclusion
91 * in FreeBSD by Justin T. Gibbs. The original work on the data structures
92 * used in this implementation was published by G. Varghese and T. Lauck in
93 * the paper "Hashed and Hierarchical Timing Wheels: Data Structures for
94 * the Efficient Implementation of a Timer Facility" in the Proceedings of
95 * the 11th ACM Annual Symposium on Operating Systems Principles,
96 * Austin, Texas Nov 1987.
98 * The per-cpu augmentation was done by Matthew Dillon.
101 #include <sys/param.h>
102 #include <sys/systm.h>
103 #include <sys/callout.h>
104 #include <sys/kernel.h>
105 #include <sys/interrupt.h>
106 #include <sys/thread.h>
108 #include <sys/thread2.h>
109 #include <sys/mplock2.h>
111 #ifndef MAX_SOFTCLOCK_STEPS
112 #define MAX_SOFTCLOCK_STEPS 100 /* Maximum allowed value of steps. */
116 struct softclock_pcpu {
117 struct callout_tailq *callwheel;
118 struct callout * volatile next;
119 struct callout *running;/* currently running callout */
120 int softticks; /* softticks index */
121 int curticks; /* per-cpu ticks counter */
123 struct thread thread;
127 typedef struct softclock_pcpu *softclock_pcpu_t;
131 * allocate more timeout table slots when table overflows.
133 static MALLOC_DEFINE(M_CALLOUT, "callout", "callout structures");
134 static int callwheelsize;
135 static int callwheelmask;
136 static struct softclock_pcpu softclock_pcpu_ary[MAXCPU];
138 static void softclock_handler(void *arg);
141 swi_softclock_setup(void *arg)
148 * Figure out how large a callwheel we need. It must be a power of 2.
150 * ncallout is primarily based on available memory, don't explode
151 * the allocations if the system has a lot of cpus.
153 target = ncallout / ncpus + 16;
156 while (callwheelsize < target)
158 callwheelmask = callwheelsize - 1;
161 * Initialize per-cpu data structures.
163 for (cpu = 0; cpu < ncpus; ++cpu) {
166 sc = &softclock_pcpu_ary[cpu];
168 sc->callwheel = kmalloc(sizeof(*sc->callwheel) * callwheelsize,
169 M_CALLOUT, M_WAITOK|M_ZERO);
170 for (i = 0; i < callwheelsize; ++i)
171 TAILQ_INIT(&sc->callwheel[i]);
174 * Mark the softclock handler as being an interrupt thread
175 * even though it really isn't, but do not allow it to
176 * preempt other threads (do not assign td_preemptable).
178 * Kernel code now assumes that callouts do not preempt
179 * the cpu they were scheduled on.
181 lwkt_create(softclock_handler, sc, NULL,
182 &sc->thread, TDF_NOSTART | TDF_INTTHREAD,
183 cpu, "softclock %d", cpu);
188 * Must occur after ncpus has been initialized.
190 SYSINIT(softclock_setup, SI_BOOT2_SOFTCLOCK, SI_ORDER_SECOND,
191 swi_softclock_setup, NULL);
194 * This routine is called from the hardclock() (basically a FASTint/IPI) on
195 * each cpu in the system. sc->curticks is this cpu's notion of the timebase.
196 * It IS NOT NECESSARILY SYNCHRONIZED WITH 'ticks'! sc->softticks is where
197 * the callwheel is currently indexed.
199 * WARNING! The MP lock is not necessarily held on call, nor can it be
202 * sc->softticks is adjusted by either this routine or our helper thread
203 * depending on whether the helper thread is running or not.
206 hardclock_softtick(globaldata_t gd)
210 sc = &softclock_pcpu_ary[gd->gd_cpuid];
214 if (sc->softticks == sc->curticks) {
216 * in sync, only wakeup the thread if there is something to
219 if (TAILQ_FIRST(&sc->callwheel[sc->softticks & callwheelmask]))
222 lwkt_schedule(&sc->thread);
228 * out of sync, wakeup the thread unconditionally so it can
232 lwkt_schedule(&sc->thread);
237 * This procedure is the main loop of our per-cpu helper thread. The
238 * sc->isrunning flag prevents us from racing hardclock_softtick() and
239 * a critical section is sufficient to interlock sc->curticks and protect
240 * us from remote IPI's / list removal.
242 * The thread starts with the MP lock released and not in a critical
243 * section. The loop itself is MP safe while individual callbacks
244 * may or may not be, so we obtain or release the MP lock as appropriate.
247 softclock_handler(void *arg)
251 struct callout_tailq *bucket;
252 void (*c_func)(void *);
257 * Run the callout thread at the same priority as other kernel
258 * threads so it can be round-robined.
260 /*lwkt_setpri_self(TDPRI_SOFT_NORM);*/
265 while (sc->softticks != (int)(sc->curticks + 1)) {
266 bucket = &sc->callwheel[sc->softticks & callwheelmask];
268 for (c = TAILQ_FIRST(bucket); c; c = sc->next) {
269 if (c->c_time != sc->softticks) {
270 sc->next = TAILQ_NEXT(c, c_links.tqe);
273 if (c->c_flags & CALLOUT_MPSAFE) {
280 * The request might be removed while we
281 * are waiting to get the MP lock. If it
282 * was removed sc->next will point to the
283 * next valid request or NULL, loop up.
293 sc->next = TAILQ_NEXT(c, c_links.tqe);
294 TAILQ_REMOVE(bucket, c, c_links.tqe);
300 KKASSERT(c->c_flags & CALLOUT_DID_INIT);
301 c->c_flags &= ~CALLOUT_PENDING;
306 /* NOTE: list may have changed */
311 lwkt_deschedule_self(&sc->thread); /* == curthread */
318 * New interface; clients allocate their own callout structures.
320 * callout_reset() - establish or change a timeout
321 * callout_stop() - disestablish a timeout
322 * callout_init() - initialize a callout structure so that it can
323 * safely be passed to callout_reset() and callout_stop()
324 * callout_init_mp() - same but any installed functions must be MP safe.
326 * <sys/callout.h> defines three convenience macros:
328 * callout_active() - returns truth if callout has not been serviced
329 * callout_pending() - returns truth if callout is still waiting for timeout
330 * callout_deactivate() - marks the callout as having been serviced
334 * Start or restart a timeout. Install the callout structure in the
335 * callwheel. Callers may legally pass any value, even if 0 or negative,
336 * but since the sc->curticks index may have already been processed a
337 * minimum timeout of 1 tick will be enforced.
339 * The callout is installed on and will be processed on the current cpu's
342 * WARNING! This function may be called from any cpu but the caller must
343 * serialize callout_stop() and callout_reset() calls on the passed
344 * structure regardless of cpu.
347 callout_reset(struct callout *c, int to_ticks, void (*ftn)(void *),
354 if ((c->c_flags & CALLOUT_DID_INIT) == 0) {
357 "callout_reset(%p) from %p: callout was not initialized\n",
358 c, ((int **)&c)[-1]);
363 sc = &softclock_pcpu_ary[gd->gd_cpuid];
366 if (c->c_flags & CALLOUT_ACTIVE)
373 c->c_flags |= (CALLOUT_ACTIVE | CALLOUT_PENDING);
375 c->c_time = sc->curticks + to_ticks;
378 TAILQ_INSERT_TAIL(&sc->callwheel[c->c_time & callwheelmask],
383 struct callout_remote_arg {
391 callout_reset_ipi(void *arg)
393 struct callout_remote_arg *rmt = arg;
395 callout_reset(rmt->c, rmt->to_ticks, rmt->ftn, rmt->arg);
399 callout_reset_bycpu(struct callout *c, int to_ticks, void (*ftn)(void *),
400 void *arg, int cpuid)
402 KASSERT(cpuid >= 0 && cpuid < ncpus, ("invalid cpuid %d", cpuid));
404 if (cpuid == mycpuid) {
405 callout_reset(c, to_ticks, ftn, arg);
407 struct globaldata *target_gd;
408 struct callout_remote_arg rmt;
414 rmt.to_ticks = to_ticks;
416 target_gd = globaldata_find(cpuid);
418 seq = lwkt_send_ipiq(target_gd, callout_reset_ipi, &rmt);
419 lwkt_wait_ipiq(target_gd, seq);
424 * Stop a running timer. WARNING! If called on a cpu other then the one
425 * the callout was started on this function will liveloop on its IPI to
426 * the target cpu to process the request. It is possible for the callout
427 * to execute in that case.
429 * WARNING! This function may be called from any cpu but the caller must
430 * serialize callout_stop() and callout_reset() calls on the passed
431 * structure regardless of cpu.
433 * WARNING! This routine may be called from an IPI
435 * WARNING! This function can return while it's c_func is still running
436 * in the callout thread, a secondary check may be needed.
437 * Use callout_stop_sync() to wait for any callout function to
438 * complete before returning, being sure that no deadlock is
439 * possible if you do.
442 callout_stop(struct callout *c)
444 globaldata_t gd = mycpu;
449 if ((c->c_flags & CALLOUT_DID_INIT) == 0) {
452 "callout_stop(%p) from %p: callout was not initialized\n",
453 c, ((int **)&c)[-1]);
460 * Don't attempt to delete a callout that's not on the queue. The
461 * callout may not have a cpu assigned to it. Callers do not have
462 * to be on the issuing cpu but must still serialize access to the
465 * We are not cpu-localized here and cannot safely modify the
466 * flags field in the callout structure. Note that most of the
467 * time CALLOUT_ACTIVE will be 0 if CALLOUT_PENDING is also 0.
469 * If we race another cpu's dispatch of this callout it is possible
470 * for CALLOUT_ACTIVE to be set with CALLOUT_PENDING unset. This
471 * will cause us to fall through and synchronize with the other
474 if ((c->c_flags & CALLOUT_PENDING) == 0) {
475 if ((c->c_flags & CALLOUT_ACTIVE) == 0) {
479 if (c->c_gd == NULL || c->c_gd == gd) {
480 c->c_flags &= ~CALLOUT_ACTIVE;
485 if ((tgd = c->c_gd) != gd) {
487 * If the callout is owned by a different CPU we have to
488 * execute the function synchronously on the target cpu.
492 cpu_ccfence(); /* don't let tgd alias c_gd */
493 seq = lwkt_send_ipiq(tgd, (void *)callout_stop, c);
494 lwkt_wait_ipiq(tgd, seq);
497 * If the callout is owned by the same CPU we can
498 * process it directly, but if we are racing our helper
499 * thread (sc->next), we have to adjust sc->next. The
500 * race is interlocked by a critical section.
502 sc = &softclock_pcpu_ary[gd->gd_cpuid];
504 c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
506 sc->next = TAILQ_NEXT(c, c_links.tqe);
508 TAILQ_REMOVE(&sc->callwheel[c->c_time & callwheelmask],
517 * Issue a callout_stop() and ensure that any callout race completes
518 * before returning. Does NOT de-initialized the callout.
521 callout_stop_sync(struct callout *c)
525 while (c->c_flags & CALLOUT_DID_INIT) {
528 sc = &softclock_pcpu_ary[c->c_gd->gd_cpuid];
529 if (sc->running == c) {
530 while (sc->running == c)
531 tsleep(&sc->running, 0, "crace", 1);
534 if ((c->c_flags & (CALLOUT_PENDING | CALLOUT_ACTIVE)) == 0)
536 kprintf("Warning: %s: callout race\n", curthread->td_comm);
541 * Terminate a callout
543 * This function will stop any pending callout and also block while the
544 * callout's function is running. It should only be used in cases where
545 * no deadlock is possible (due to the callout function acquiring locks
546 * that the current caller of callout_terminate() already holds), when
547 * the caller is ready to destroy the callout structure.
549 * This function clears the CALLOUT_DID_INIT flag.
551 * lwkt_token locks are ok.
554 callout_terminate(struct callout *c)
558 if (c->c_flags & CALLOUT_DID_INIT) {
560 sc = &softclock_pcpu_ary[c->c_gd->gd_cpuid];
561 if (sc->running == c) {
562 while (sc->running == c)
563 tsleep(&sc->running, 0, "crace", 1);
565 KKASSERT((c->c_flags & (CALLOUT_PENDING|CALLOUT_ACTIVE)) == 0);
566 c->c_flags &= ~CALLOUT_DID_INIT;
571 * Prepare a callout structure for use by callout_reset() and/or
572 * callout_stop(). The MP version of this routine requires that the callback
573 * function installed by callout_reset() be MP safe.
575 * The init functions can be called from any cpu and do not have to be
576 * called from the cpu that the timer will eventually run on.
579 callout_init(struct callout *c)
582 c->c_flags = CALLOUT_DID_INIT;
586 callout_init_mp(struct callout *c)
589 c->c_flags |= CALLOUT_MPSAFE;