428 lines
11 KiB
C
428 lines
11 KiB
C
/* $NetBSD: subr_xcall.c,v 1.15 2013/04/07 00:31:40 rmind Exp $ */
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/*-
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* Copyright (c) 2007-2010 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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* by Andrew Doran and Mindaugas Rasiukevicius.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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/*
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* Cross call support
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*
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* Background
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*
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* Sometimes it is necessary to modify hardware state that is tied
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* directly to individual CPUs (such as a CPU's local timer), and
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* these updates can not be done remotely by another CPU. The LWP
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* requesting the update may be unable to guarantee that it will be
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* running on the CPU where the update must occur, when the update
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* occurs.
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*
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* Additionally, it's sometimes necessary to modify per-CPU software
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* state from a remote CPU. Where these update operations are so
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* rare or the access to the per-CPU data so frequent that the cost
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* of using locking or atomic operations to provide coherency is
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* prohibitive, another way must be found.
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*
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* Cross calls help to solve these types of problem by allowing
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* any CPU in the system to request that an arbitrary function be
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* executed on any other CPU.
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*
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* Implementation
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*
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* A slow mechanism for making 'low priority' cross calls is
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* provided. The function to be executed runs on the remote CPU
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* within a bound kthread. No queueing is provided, and the
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* implementation uses global state. The function being called may
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* block briefly on locks, but in doing so must be careful to not
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* interfere with other cross calls in the system. The function is
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* called with thread context and not from a soft interrupt, so it
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* can ensure that it is not interrupting other code running on the
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* CPU, and so has exclusive access to the CPU. Since this facility
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* is heavyweight, it's expected that it will not be used often.
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*
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* Cross calls must not allocate memory, as the pagedaemon uses
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* them (and memory allocation may need to wait on the pagedaemon).
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*
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* A low-overhead mechanism for high priority calls (XC_HIGHPRI) is
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* also provided. The function to be executed runs on a software
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* interrupt context, at SOFTINT_CLOCK level, and is expected to be
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* very lightweight, e.g. avoid blocking.
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*/
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#include <sys/cdefs.h>
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__KERNEL_RCSID(0, "$NetBSD: subr_xcall.c,v 1.15 2013/04/07 00:31:40 rmind Exp $");
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#include <sys/types.h>
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#include <sys/param.h>
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#include <sys/xcall.h>
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#include <sys/mutex.h>
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#include <sys/condvar.h>
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#include <sys/evcnt.h>
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#include <sys/kthread.h>
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#include <sys/cpu.h>
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#ifdef _RUMPKERNEL
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#include "rump_private.h"
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#endif
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/* Cross-call state box. */
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typedef struct {
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kmutex_t xc_lock;
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kcondvar_t xc_busy;
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xcfunc_t xc_func;
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void * xc_arg1;
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void * xc_arg2;
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uint64_t xc_headp;
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uint64_t xc_donep;
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} xc_state_t;
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/* Bit indicating high (1) or low (0) priority. */
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#define XC_PRI_BIT (1ULL << 63)
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/* Low priority xcall structures. */
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static xc_state_t xc_low_pri __cacheline_aligned;
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static uint64_t xc_tailp __cacheline_aligned;
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/* High priority xcall structures. */
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static xc_state_t xc_high_pri __cacheline_aligned;
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static void * xc_sih __cacheline_aligned;
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/* Event counters. */
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static struct evcnt xc_unicast_ev __cacheline_aligned;
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static struct evcnt xc_broadcast_ev __cacheline_aligned;
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static void xc_init(void);
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static void xc_thread(void *);
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static inline uint64_t xc_highpri(xcfunc_t, void *, void *, struct cpu_info *);
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static inline uint64_t xc_lowpri(xcfunc_t, void *, void *, struct cpu_info *);
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/*
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* xc_init:
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*
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* Initialize low and high priority cross-call structures.
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*/
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static void
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xc_init(void)
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{
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xc_state_t *xclo = &xc_low_pri, *xchi = &xc_high_pri;
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memset(xclo, 0, sizeof(xc_state_t));
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mutex_init(&xclo->xc_lock, MUTEX_DEFAULT, IPL_NONE);
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cv_init(&xclo->xc_busy, "xclocv");
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xc_tailp = 0;
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memset(xchi, 0, sizeof(xc_state_t));
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mutex_init(&xchi->xc_lock, MUTEX_DEFAULT, IPL_SOFTCLOCK);
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cv_init(&xchi->xc_busy, "xchicv");
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xc_sih = softint_establish(SOFTINT_CLOCK | SOFTINT_MPSAFE,
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xc__highpri_intr, NULL);
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KASSERT(xc_sih != NULL);
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evcnt_attach_dynamic(&xc_unicast_ev, EVCNT_TYPE_MISC, NULL,
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"crosscall", "unicast");
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evcnt_attach_dynamic(&xc_broadcast_ev, EVCNT_TYPE_MISC, NULL,
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"crosscall", "broadcast");
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}
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/*
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* xc_init_cpu:
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*
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* Initialize the cross-call subsystem. Called once for each CPU
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* in the system as they are attached.
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*/
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void
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xc_init_cpu(struct cpu_info *ci)
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{
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static bool again = false;
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int error;
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if (!again) {
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/* Autoconfiguration will prevent re-entry. */
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xc_init();
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again = true;
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}
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cv_init(&ci->ci_data.cpu_xcall, "xcall");
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error = kthread_create(PRI_XCALL, KTHREAD_MPSAFE, ci, xc_thread,
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NULL, NULL, "xcall/%u", ci->ci_index);
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KASSERT(error == 0);
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}
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/*
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* xc_broadcast:
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*
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* Trigger a call on all CPUs in the system.
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*/
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uint64_t
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xc_broadcast(u_int flags, xcfunc_t func, void *arg1, void *arg2)
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{
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KASSERT(!cpu_intr_p() && !cpu_softintr_p());
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if ((flags & XC_HIGHPRI) != 0) {
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return xc_highpri(func, arg1, arg2, NULL);
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} else {
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return xc_lowpri(func, arg1, arg2, NULL);
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}
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}
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/*
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* xc_unicast:
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*
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* Trigger a call on one CPU.
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*/
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uint64_t
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xc_unicast(u_int flags, xcfunc_t func, void *arg1, void *arg2,
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struct cpu_info *ci)
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{
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KASSERT(ci != NULL);
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KASSERT(!cpu_intr_p() && !cpu_softintr_p());
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if ((flags & XC_HIGHPRI) != 0) {
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return xc_highpri(func, arg1, arg2, ci);
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} else {
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return xc_lowpri(func, arg1, arg2, ci);
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}
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}
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/*
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* xc_wait:
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*
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* Wait for a cross call to complete.
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*/
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void
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xc_wait(uint64_t where)
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{
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xc_state_t *xc;
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KASSERT(!cpu_intr_p() && !cpu_softintr_p());
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/* Determine whether it is high or low priority cross-call. */
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if ((where & XC_PRI_BIT) != 0) {
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xc = &xc_high_pri;
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where &= ~XC_PRI_BIT;
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} else {
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xc = &xc_low_pri;
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}
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/* Fast path, if already done. */
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if (xc->xc_donep >= where) {
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return;
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}
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/* Slow path: block until awoken. */
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mutex_enter(&xc->xc_lock);
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while (xc->xc_donep < where) {
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cv_wait(&xc->xc_busy, &xc->xc_lock);
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}
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mutex_exit(&xc->xc_lock);
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}
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/*
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* xc_lowpri:
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*
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* Trigger a low priority call on one or more CPUs.
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*/
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static inline uint64_t
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xc_lowpri(xcfunc_t func, void *arg1, void *arg2, struct cpu_info *ci)
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{
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xc_state_t *xc = &xc_low_pri;
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CPU_INFO_ITERATOR cii;
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uint64_t where;
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mutex_enter(&xc->xc_lock);
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while (xc->xc_headp != xc_tailp) {
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cv_wait(&xc->xc_busy, &xc->xc_lock);
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}
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xc->xc_arg1 = arg1;
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xc->xc_arg2 = arg2;
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xc->xc_func = func;
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if (ci == NULL) {
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xc_broadcast_ev.ev_count++;
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for (CPU_INFO_FOREACH(cii, ci)) {
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if ((ci->ci_schedstate.spc_flags & SPCF_RUNNING) == 0)
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continue;
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xc->xc_headp += 1;
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ci->ci_data.cpu_xcall_pending = true;
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cv_signal(&ci->ci_data.cpu_xcall);
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}
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} else {
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xc_unicast_ev.ev_count++;
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xc->xc_headp += 1;
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ci->ci_data.cpu_xcall_pending = true;
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cv_signal(&ci->ci_data.cpu_xcall);
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}
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KASSERT(xc_tailp < xc->xc_headp);
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where = xc->xc_headp;
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mutex_exit(&xc->xc_lock);
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/* Return a low priority ticket. */
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KASSERT((where & XC_PRI_BIT) == 0);
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return where;
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}
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/*
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* xc_thread:
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*
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* One thread per-CPU to dispatch low priority calls.
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*/
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static void
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xc_thread(void *cookie)
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{
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struct cpu_info *ci = curcpu();
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xc_state_t *xc = &xc_low_pri;
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void *arg1, *arg2;
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xcfunc_t func;
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mutex_enter(&xc->xc_lock);
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for (;;) {
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while (!ci->ci_data.cpu_xcall_pending) {
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if (xc->xc_headp == xc_tailp) {
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cv_broadcast(&xc->xc_busy);
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}
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cv_wait(&ci->ci_data.cpu_xcall, &xc->xc_lock);
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KASSERT(ci == curcpu());
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}
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ci->ci_data.cpu_xcall_pending = false;
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func = xc->xc_func;
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arg1 = xc->xc_arg1;
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arg2 = xc->xc_arg2;
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xc_tailp++;
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mutex_exit(&xc->xc_lock);
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KASSERT(func != NULL);
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(*func)(arg1, arg2);
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mutex_enter(&xc->xc_lock);
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xc->xc_donep++;
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}
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/* NOTREACHED */
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}
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/*
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* xc_ipi_handler:
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*
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* Handler of cross-call IPI.
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*/
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void
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xc_ipi_handler(void)
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{
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/* Executes xc__highpri_intr() via software interrupt. */
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softint_schedule(xc_sih);
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}
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/*
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* xc__highpri_intr:
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*
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* A software interrupt handler for high priority calls.
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*/
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void
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xc__highpri_intr(void *dummy)
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{
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xc_state_t *xc = &xc_high_pri;
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void *arg1, *arg2;
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xcfunc_t func;
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KASSERT(!cpu_intr_p());
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/*
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* Lock-less fetch of function and its arguments.
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* Safe since it cannot change at this point.
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*/
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KASSERT(xc->xc_donep < xc->xc_headp);
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func = xc->xc_func;
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arg1 = xc->xc_arg1;
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arg2 = xc->xc_arg2;
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KASSERT(func != NULL);
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(*func)(arg1, arg2);
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/*
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* Note the request as done, and if we have reached the head,
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* cross-call has been processed - notify waiters, if any.
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*/
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mutex_enter(&xc->xc_lock);
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if (++xc->xc_donep == xc->xc_headp) {
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cv_broadcast(&xc->xc_busy);
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}
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mutex_exit(&xc->xc_lock);
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}
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/*
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* xc_highpri:
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*
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* Trigger a high priority call on one or more CPUs.
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*/
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static inline uint64_t
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xc_highpri(xcfunc_t func, void *arg1, void *arg2, struct cpu_info *ci)
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{
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xc_state_t *xc = &xc_high_pri;
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uint64_t where;
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mutex_enter(&xc->xc_lock);
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while (xc->xc_headp != xc->xc_donep) {
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cv_wait(&xc->xc_busy, &xc->xc_lock);
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}
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xc->xc_func = func;
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xc->xc_arg1 = arg1;
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xc->xc_arg2 = arg2;
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xc->xc_headp += (ci ? 1 : ncpu);
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where = xc->xc_headp;
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mutex_exit(&xc->xc_lock);
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/*
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* Send the IPI once lock is released.
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* Note: it will handle the local CPU case.
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*/
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#ifdef _RUMPKERNEL
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rump_xc_highpri(ci);
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#else
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#ifdef MULTIPROCESSOR
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kpreempt_disable();
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if (curcpu() == ci) {
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/* Unicast: local CPU. */
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xc_ipi_handler();
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} else if (ci) {
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/* Unicast: remote CPU. */
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xc_send_ipi(ci);
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} else {
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/* Broadcast: all, including local. */
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xc_send_ipi(NULL);
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xc_ipi_handler();
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}
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kpreempt_enable();
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#else
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KASSERT(ci == NULL || curcpu() == ci);
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xc_ipi_handler();
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#endif
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#endif
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/* Indicate a high priority ticket. */
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return (where | XC_PRI_BIT);
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}
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