/* $NetBSD: subr_pserialize.c,v 1.4 2011/08/07 21:38:32 rmind Exp $ */ /*- * Copyright (c) 2010, 2011 The NetBSD Foundation, Inc. * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. */ /* * Passive serialization. * * Implementation accurately matches the lapsed US patent 4809168, therefore * code is patent-free in the United States. Your use of this code is at * your own risk. * * Note for NetBSD developers: all changes to this source file must be * approved by the . */ #include __KERNEL_RCSID(0, "$NetBSD: subr_pserialize.c,v 1.4 2011/08/07 21:38:32 rmind Exp $"); #include #include #include #include #include #include #include #include #include struct pserialize { TAILQ_ENTRY(pserialize) psz_chain; lwp_t * psz_owner; kcondvar_t psz_notifier; kcpuset_t * psz_target; kcpuset_t * psz_pass; }; static u_int psz_work_todo __cacheline_aligned; static kmutex_t psz_lock __cacheline_aligned; static struct evcnt psz_ev_excl __cacheline_aligned; /* * As defined in "Method 1": * q0: "0 MP checkpoints have occured". * q1: "1 MP checkpoint has occured". * q2: "2 MP checkpoints have occured". */ static TAILQ_HEAD(, pserialize) psz_queue0 __cacheline_aligned; static TAILQ_HEAD(, pserialize) psz_queue1 __cacheline_aligned; static TAILQ_HEAD(, pserialize) psz_queue2 __cacheline_aligned; /* * pserialize_init: * * Initialize passive serialization structures. */ void pserialize_init(void) { psz_work_todo = 0; TAILQ_INIT(&psz_queue0); TAILQ_INIT(&psz_queue1); TAILQ_INIT(&psz_queue2); mutex_init(&psz_lock, MUTEX_DEFAULT, IPL_SCHED); evcnt_attach_dynamic(&psz_ev_excl, EVCNT_TYPE_MISC, NULL, "pserialize", "exclusive access"); } /* * pserialize_create: * * Create and initialize a passive serialization object. */ pserialize_t pserialize_create(void) { pserialize_t psz; psz = kmem_zalloc(sizeof(struct pserialize), KM_SLEEP); cv_init(&psz->psz_notifier, "psrlz"); kcpuset_create(&psz->psz_target, true); kcpuset_create(&psz->psz_pass, true); psz->psz_owner = NULL; return psz; } /* * pserialize_destroy: * * Destroy a passive serialization object. */ void pserialize_destroy(pserialize_t psz) { KASSERT(psz->psz_owner == NULL); cv_destroy(&psz->psz_notifier); kcpuset_destroy(psz->psz_target); kcpuset_destroy(psz->psz_pass); kmem_free(psz, sizeof(struct pserialize)); } /* * pserialize_perform: * * Perform the write side of passive serialization. The calling * thread holds an exclusive lock on the data object(s) being updated. * We wait until every processor in the system has made at least two * passes through cpu_swichto(). The wait is made with the caller's * update lock held, but is short term. */ void pserialize_perform(pserialize_t psz) { KASSERT(!cpu_intr_p()); KASSERT(!cpu_softintr_p()); if (__predict_false(panicstr != NULL)) { return; } KASSERT(psz->psz_owner == NULL); KASSERT(ncpu > 0); /* * Set up the object and put it onto the queue. The lock * activity here provides the necessary memory barrier to * make the caller's data update completely visible to * other processors. */ psz->psz_owner = curlwp; kcpuset_copy(psz->psz_target, kcpuset_attached); kcpuset_zero(psz->psz_pass); mutex_spin_enter(&psz_lock); TAILQ_INSERT_TAIL(&psz_queue0, psz, psz_chain); psz_work_todo++; mutex_spin_exit(&psz_lock); /* * Force some context switch activity on every CPU, as the system * may not be busy. Note: should pass the point twice. */ xc_broadcast(XC_HIGHPRI, (xcfunc_t)nullop, NULL, NULL); xc_broadcast(XC_HIGHPRI, (xcfunc_t)nullop, NULL, NULL); /* * Wait for all CPUs to cycle through mi_switch() twice. * The last one through will remove our update from the * queue and awaken us. */ mutex_spin_enter(&psz_lock); while (!kcpuset_iszero(psz->psz_target)) { cv_wait(&psz->psz_notifier, &psz_lock); } psz_ev_excl.ev_count++; mutex_spin_exit(&psz_lock); psz->psz_owner = NULL; } int pserialize_read_enter(void) { KASSERT(!cpu_intr_p()); return splsoftclock(); } void pserialize_read_exit(int s) { splx(s); } /* * pserialize_switchpoint: * * Monitor system context switch activity. Called from machine * independent code after mi_switch() returns. */ void pserialize_switchpoint(void) { pserialize_t psz, next; cpuid_t cid; /* * If no updates pending, bail out. No need to lock in order to * test psz_work_todo; the only ill effect of missing an update * would be to delay LWPs waiting in pserialize_perform(). That * will not happen because updates are on the queue before an * xcall is generated (serialization) to tickle every CPU. */ if (__predict_true(psz_work_todo == 0)) { return; } mutex_spin_enter(&psz_lock); cid = cpu_index(curcpu()); /* * At first, scan through the second queue and update each request, * if passed all processors, then transfer to the third queue. */ for (psz = TAILQ_FIRST(&psz_queue1); psz != NULL; psz = next) { next = TAILQ_NEXT(psz, psz_chain); if (!kcpuset_match(psz->psz_pass, psz->psz_target)) { kcpuset_set(psz->psz_pass, cid); continue; } kcpuset_zero(psz->psz_pass); TAILQ_REMOVE(&psz_queue1, psz, psz_chain); TAILQ_INSERT_TAIL(&psz_queue2, psz, psz_chain); } /* * Scan through the first queue and update each request, * if passed all processors, then move to the second queue. */ for (psz = TAILQ_FIRST(&psz_queue0); psz != NULL; psz = next) { next = TAILQ_NEXT(psz, psz_chain); if (!kcpuset_match(psz->psz_pass, psz->psz_target)) { kcpuset_set(psz->psz_pass, cid); continue; } kcpuset_zero(psz->psz_pass); TAILQ_REMOVE(&psz_queue0, psz, psz_chain); TAILQ_INSERT_TAIL(&psz_queue1, psz, psz_chain); } /* * Process the third queue: entries have been seen twice on every * processor, remove from the queue and notify the updating thread. */ while ((psz = TAILQ_FIRST(&psz_queue2)) != NULL) { TAILQ_REMOVE(&psz_queue2, psz, psz_chain); kcpuset_zero(psz->psz_target); cv_signal(&psz->psz_notifier); psz_work_todo--; } mutex_spin_exit(&psz_lock); }