215 lines
8.2 KiB
Groff
215 lines
8.2 KiB
Groff
.\" $NetBSD: softintr.9,v 1.18 2008/10/06 13:51:38 pooka 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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.\" Copyright (c) 2000 Christopher G. Demetriou.
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.\" All rights reserved.
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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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed for the
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.\" NetBSD Project. See http://www.NetBSD.org/ for
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.\" information about NetBSD.
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.\" 4. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" --(license Id: LICENSE.proto,v 1.1 2000/06/13 21:40:26 cgd Exp )--
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.\"
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.Dd October 6, 2008
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.Dt SOFTINT 9
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.Os
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.Sh NAME
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.Nm softint ,
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.Nm softint_establish ,
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.Nm softint_disestablish ,
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.Nm softint_schedule
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.Nd machine-independent software interrupt framework
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.Sh SYNOPSIS
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.In sys/intr.h
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.Ft void *
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.Fn softint_establish "u_int flags" "void (*func)(void *)" "void *arg"
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.Ft void
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.Fn softint_disestablish "void *cookie"
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.Ft void
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.Fn softint_schedule "void *cookie"
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.Sh DESCRIPTION
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The software interrupt framework is designed to provide
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a generic software interrupt mechanism which can be used any time a
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low-priority callback is needed.
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.Pp
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It allows dynamic registration of software interrupts for loadable
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drivers and protocol stacks, prioritization and fair queueing of software
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interrupts, and allows machine-dependent optimizations to reduce cost.
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.Pp
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Four priority levels are provided.
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In order of priority (lowest to highest) the levels are: clock, bio,
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net, serial.
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The names are symbolic and in isolation do not have any direct
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connection with a particular kind of device activity: they are
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only meant as a guide.
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.Pp
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The four priority levels map directly to scheduler priority
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levels, and where the architecture implements 'fast' software
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interrupts, they also map onto interrupt priorities.
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The interrupt priorities are intended to be hidden from machine
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independent code, which should in general use thread-safe mechanisms
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to synchronize with software interrupts (for example: mutexes).
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.Pp
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Software interrupts run with limited machine context.
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In particular, they do not possess any address space context.
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They should not try to operate on user space addresses, or to use
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virtual memory facilities other than those noted as interrupt
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safe.
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Unlike hardware interrupts, software interrupts do have thread
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context.
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They may block on synchronization objects, sleep, and resume
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execution at a later time.
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.Pp
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Since software interrupts are a limited resource and run with
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higher priority than most other LWPs in the system, all
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block-and-resume activity by a software interrupt must be kept
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short to allow further processing at that level to continue.
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By extension, code running with process context must take care to
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ensure that any lock that may be taken from a software interrupt
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can not be held for more than a short period of time.
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.Pp
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The kernel does not allow software interrupts to use facilities
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or perform actions that are likely to block for a significant
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amount of time.
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This means that it's not valid for a software interrupt to
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sleep on condition variables or to wait for resources to
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become available (for example, memory).
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.Pp
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The following is a brief description of each function in the framework:
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.Bl -tag -width abcxdcc
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.It Fn softint_establish flags func arg
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.Pp
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Register a software interrupt.
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The
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.Fa flags
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value must contain one of the following constants, specifing
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the priority level for the soft interrupt:
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.Pp
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.Dv SOFTINT_CLOCK ,
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.Dv SOFTINT_BIO ,
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.Dv SOFTINT_NET ,
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.Dv SOFTINT_SERIAL
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.Pp
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If the constant
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.Dv SOFTINT_MPSAFE
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is not logically ORed into
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.Fa flags ,
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the global
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.Dv kernel_lock
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will automatically be acquired before the soft interrupt handler
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is called.
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.Pp
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The constant
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.Fa func
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specifies the function to call when the soft interrupt is
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executed.
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The argument
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.Fa arg
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will be passed to this function.
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.Pp
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.Fn softint_establish
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may block in order to allocate memory.
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If successful, it returns a
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.Pf non- Dv NULL
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opaque value to be used as an argument to
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.Fn softint_schedule
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and/or
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.Fn softint_disestablish .
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If for some reason it does not succeed, it returns
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.Dv NULL .
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.It Fn softint_disestablish cookie
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.Pp
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Deallocate a software interrupt previously allocated
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by a call to
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.Fn softint_establish .
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.\" XXX What happens to pending scheduled calls?
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.It Fn softint_schedule cookie
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.Pp
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Schedule a software interrupt previously allocated
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by a call to
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.Fn softint_establish
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to be executed as soon as that software interrupt is unblocked.
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.Fn softint_schedule
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can safely be called multiple times before the
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callback routine is invoked.
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.Pp
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Soft interrupt scheduling is CPU-local.
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A request to dispatch a soft interrupt will only be serviced on
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the same CPU where the request was made.
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The LWPs (light weight processes) dedicated to soft interrupt
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processing are bound to their home CPUs, so if a soft interrupt
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handler sleeps and later resumes, it will always resume on the
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same CPU.
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.Pp
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On a system with multiple processors, multiple instances of
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the same soft interrupt handler can be in flight simultaneously
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(at most one per-CPU).
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.El
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.Sh SEE ALSO
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.Xr mutex 9 ,
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.Xr rwlock 9 ,
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.Xr spl 9
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.Sh HISTORY
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The
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.Nx
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machine-independent software interrupt framework was designed in 1997
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and was implemented by one port in
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.Nx 1.3 .
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However, it did not gain wider implementation until
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.Nx 1.5 .
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Between
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.Nx 4.0
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and
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.Nx 5.0
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the framework was re-implemented in a machine-independant way to
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provide software interrupts with thread context.
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