164 lines
4.3 KiB
Groff
164 lines
4.3 KiB
Groff
.\" $NetBSD: percpu.9,v 1.12 2017/05/31 23:54:17 chs Exp $
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.\"
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.\" Copyright (c) 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 David Young.
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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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.Dd May 31, 2017
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.Dt PERCPU 9
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.Os
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.Sh NAME
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.Nm percpu ,
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.Nm percpu_alloc ,
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.Nm percpu_free ,
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.Nm percpu_getref ,
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.Nm percpu_putref ,
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.Nm percpu_foreach
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.Nd per-CPU storage allocator
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.Sh SYNOPSIS
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.In sys/percpu.h
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.Vt typedef void (*percpu_callback_t)(void *, void *, struct cpu_info *);
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.Ft percpu_t *
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.Fn percpu_alloc "size_t size"
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.Ft void
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.Fn percpu_free "percpu_t *pc" "size_t size"
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.Ft void *
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.Fn percpu_getref "percpu_t *pc"
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.Ft void
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.Fn percpu_putref "percpu_t *pc"
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.Ft void
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.Fn percpu_foreach "percpu_t *pc" "percpu_callback_t cb" "void *arg"
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.Sh DESCRIPTION
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The machine-independent
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.Nm
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interface provides per-CPU, CPU-local memory reservations to kernel
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subsystems.
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.Fo percpu_alloc
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.Fa size
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.Fc
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reserves on each CPU an independent memory region of
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.Fa size
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bytes that is local to that CPU, returning a handle
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.Po
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.Vt percpu_t
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.Pc
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to those regions.
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A thread may subsequently ask for a pointer,
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.Fa p ,
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to the region held by the
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.Vt percpu_t
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on the thread's current CPU.
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Until the thread relinquishes the pointer, or voluntarily sleeps,
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the thread may read or write the region at
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.Fa p
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without causing interprocessor memory synchronization.
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.Sh FUNCTIONS
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.Bl -tag -width compact
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.It Fn percpu_alloc "size"
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Call this in thread context to allocate
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.Fa size
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bytes of local storage on each CPU.
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The storage is initialized with zeroes.
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Treat this as an expensive operation.
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.Fn percpu_alloc
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returns a handle for the per-CPU storage.
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.It Fn percpu_free "pc" "size"
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Call this in thread context to
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return to the system the per-CPU storage held by
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.Fa pc .
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.Fa size
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should match the
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.Fa size
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passed to
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.Fn percpu_alloc .
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When
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.Fn percpu_free
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returns,
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.Fa pc
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is undefined.
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Treat this as an expensive operation.
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.It Fn percpu_getref "pc"
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Disable preemption and return a pointer to the storage held by
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.Fa pc
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on the local CPU.
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Use
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.Fn percpu_getref
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in either thread or interrupt context.
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Follow each
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.Fn percpu_getref
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call with a matching call to
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.Fn percpu_putref .
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.It Fn percpu_putref "pc"
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Indicate that the thread is finished
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with the pointer returned by the matching
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call to
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.Fn percpu_getref .
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Re-enables preemption.
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.It Fn percpu_foreach "pc" "cb" "arg"
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On each CPU, for
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.Fa ci
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the corresponding
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.Vt "struct cpu_info *"
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and
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.Fa "p"
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the CPU-local storage held by
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.Fa pc ,
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run
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.Fo "(*cb)"
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.Fa "p"
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.Fa "arg"
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.Fa "ci"
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.Fc .
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Call this in thread context.
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.Fa cb
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should be non-blocking and fast.
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Do not rely on
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.Fa cb
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to be run on the CPUs in any particular order.
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.El
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.Sh CODE REFERENCES
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The
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.Nm
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interface is implemented within the file
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.Pa sys/kern/subr_percpu.c .
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.\" .Sh EXAMPLES
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.Sh SEE ALSO
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.Xr atomic_ops 3 ,
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.Xr kmem 9 ,
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.Xr pcq 9 ,
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.Xr pool_cache 9 ,
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.Xr xcall 9
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.Sh HISTORY
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The
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.Nm
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interface first appeared in
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.Nx 6.0 .
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.Sh AUTHORS
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.An YAMAMOTO Takashi Aq Mt yamt@NetBSD.org
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.\" .Sh CAVEATS
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.\" .Sh BUGS
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.\" .Sh SECURITY CONSIDERATIONS
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