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/* $NetBSD: subr_pserialize.c,v 1.7 2013/02/07 23:37:58 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 <core>.
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: subr_pserialize.c,v 1.7 2013/02/07 23:37:58 rmind Exp $");
#include <sys/param.h>
#include <sys/condvar.h>
#include <sys/cpu.h>
#include <sys/evcnt.h>
#include <sys/kmem.h>
#include <sys/mutex.h>
#include <sys/pserialize.h>
#include <sys/proc.h>
#include <sys/queue.h>
#include <sys/xcall.h>
struct pserialize {
TAILQ_ENTRY(pserialize) psz_chain;
lwp_t * psz_owner;
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);
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);
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)
{
uint64_t xc;
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_running);
kcpuset_zero(psz->psz_pass);
mutex_spin_enter(&psz_lock);
TAILQ_INSERT_TAIL(&psz_queue0, psz, psz_chain);
psz_work_todo++;
do {
mutex_spin_exit(&psz_lock);
/*
* Force some context switch activity on every CPU, as
* the system may not be busy. Pause to not flood.
*/
xc = xc_broadcast(XC_HIGHPRI, (xcfunc_t)nullop, NULL, NULL);
xc_wait(xc);
kpause("psrlz", false, 1, NULL);
mutex_spin_enter(&psz_lock);
} while (!kcpuset_iszero(psz->psz_target));
psz_ev_excl.ev_count++;
mutex_spin_exit(&psz_lock);
psz->psz_owner = NULL;
}
int
pserialize_read_enter(void)
{
KASSERT(!cpu_intr_p());
return splsoftserial();
}
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);
kcpuset_set(psz->psz_pass, cid);
if (!kcpuset_match(psz->psz_pass, psz->psz_target)) {
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);
kcpuset_set(psz->psz_pass, cid);
if (!kcpuset_match(psz->psz_pass, psz->psz_target)) {
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);
psz_work_todo--;
}
mutex_spin_exit(&psz_lock);
}
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