260 lines
7.0 KiB
C
260 lines
7.0 KiB
C
/* $NetBSD: subr_xcall.c,v 1.9 2008/04/28 20:24:04 martin Exp $ */
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/*-
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* Copyright (c) 2007, 2008 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.
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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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* Future directions
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*
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* Add a low-overhead mechanism to run cross calls in interrupt
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* context (XC_HIGHPRI).
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*/
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#include <sys/cdefs.h>
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__KERNEL_RCSID(0, "$NetBSD: subr_xcall.c,v 1.9 2008/04/28 20:24:04 martin 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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static void xc_thread(void *);
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static uint64_t xc_lowpri(u_int, xcfunc_t, void *, void *, struct cpu_info *);
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static kmutex_t xc_lock;
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static xcfunc_t xc_func;
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static void *xc_arg1;
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static void *xc_arg2;
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static kcondvar_t xc_busy;
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static struct evcnt xc_unicast_ev;
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static struct evcnt xc_broadcast_ev;
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static uint64_t xc_headp;
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static uint64_t xc_tailp;
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static uint64_t xc_donep;
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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;
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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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again = true;
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mutex_init(&xc_lock, MUTEX_DEFAULT, IPL_NONE);
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cv_init(&xc_busy, "xcallbsy");
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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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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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if (error != 0)
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panic("xc_init_cpu: error %d", error);
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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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if ((flags & XC_HIGHPRI) != 0) {
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panic("xc_broadcast: no high priority crosscalls yet");
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} else {
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return xc_lowpri(flags, 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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if ((flags & XC_HIGHPRI) != 0) {
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panic("xc_unicast: no high priority crosscalls yet");
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} else {
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KASSERT(ci != NULL);
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return xc_lowpri(flags, func, arg1, arg2, ci);
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}
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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 uint64_t
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xc_lowpri(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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CPU_INFO_ITERATOR cii;
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u_int where;
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mutex_enter(&xc_lock);
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while (xc_headp != xc_tailp)
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cv_wait(&xc_busy, &xc_lock);
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xc_arg1 = arg1;
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xc_arg2 = arg2;
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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_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_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_headp);
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where = xc_headp;
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mutex_exit(&xc_lock);
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return where;
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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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if (xc_donep >= where)
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return;
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mutex_enter(&xc_lock);
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while (xc_donep < where)
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cv_wait(&xc_busy, &xc_lock);
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mutex_exit(&xc_lock);
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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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void *arg1, *arg2;
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struct cpu_info *ci;
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xcfunc_t func;
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ci = curcpu();
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mutex_enter(&xc_lock);
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for (;;) {
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while (!ci->ci_data.cpu_xcall_pending) {
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if (xc_headp == xc_tailp)
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cv_broadcast(&xc_busy);
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cv_wait(&ci->ci_data.cpu_xcall, &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_func;
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arg1 = xc_arg1;
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arg2 = xc_arg2;
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xc_tailp++;
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mutex_exit(&xc_lock);
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(*func)(arg1, arg2);
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mutex_enter(&xc_lock);
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xc_donep++;
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}
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/* NOTREACHED */
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}
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