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.\"	$OpenBSD: cpumem_get.9,v 1.11 2020/08/27 09:29:16 fcambus Exp $
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.\" Copyright (c) 2016 David Gwynne <dlg@openbsd.org>
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.Dd $Mdocdate: August 27 2020 $
.Dt CPUMEM_GET 9
.Os
.Sh NAME
.Nm cpumem_get ,
.Nm cpumem_put ,
.Nm cpumem_malloc ,
.Nm cpumem_malloc_ncpus ,
.Nm cpumem_free ,
.Nm CPUMEM_BOOT_MEMORY ,
.Nm CPUMEM_BOOT_INITIALIZER ,
.Nm cpumem_enter ,
.Nm cpumem_leave ,
.Nm cpumem_first ,
.Nm cpumem_next ,
.Nm CPUMEM_FOREACH
.Nd per CPU memory allocations
.Sh SYNOPSIS
.In sys/percpu.h
.Ft struct cpumem *
.Fn cpumem_get "struct pool *pp"
.Ft void
.Fn cpumem_put "struct pool *pp" "struct cpumem *cm"
.Ft struct cpumem *
.Fn cpumem_malloc "size_t sz" "int type"
.Ft struct cpumem *
.Fn cpumem_malloc_ncpus "struct cpumem *cm" "size_t sz" "int type"
.Ft void
.Fn cpumem_free "struct cpumem *cm" "int type" "size_t sz"
.Fn CPUMEM_BOOT_MEMORY "NAME" "size_t sz"
.Fn CPUMEM_BOOT_INITIALIZER "NAME"
.Ft void *
.Fn cpumem_enter "struct cpumem *cm"
.Ft void
.Fn cpumem_leave "struct cpumem *cm" "void *m"
.Ft void *
.Fn cpumem_first "struct cpumem_iter *ci" "struct cpumem *cm"
.Ft void *
.Fn cpumem_next "struct cpumem_iter *ci" "struct cpumem *cm"
.Fn CPUMEM_FOREACH "VARNAME" "struct cpumem_iter *ci" "struct cpumem *cm"
.Sh DESCRIPTION
The per CPU memory API provides wrappers around the allocation of
and access to per CPU memory.
.Pp
An alternate implementation of the API is provided on uni-processor
(i.e. when the kernel is not built with
.Dv MULTIPROCESSOR
defined)
systems that provides no overhead compared to direct access to a
data structure.
This allows the API to be used without affecting the performance
on uni-processor systems.
.Ss Per CPU Memory Allocation and Deallocation
.Fn cpumem_get
allocates memory for each CPU from the
.Fa pp
pool.
The memory will be zeroed on allocation.
.Pp
.Fn cpumem_put
returns each CPUs memory allocation referenced by
.Fa cm
to the
.Fa pp
pool.
.Pp
.Fn cpumem_malloc
allocates
.Fa sz
bytes of
.Fa type
memory for each CPU using
.Xr malloc 9 .
The memory will be zeroed on allocation.
.Pp
.Fn cpumem_free
returns each CPU's memory allocation referenced by
.Fa cm
to the system using
.Xr free 9 .
The same object size and type originally provided to
.Fn cpumem_malloc
must be specified by
.Fa sz
and
.Fa type
respectively.
.Pp
.Fn cpumem_get
and
.Fn cpumem_malloc
may only be used after all the CPUs in the system have been attached.
If per CPU memory needs to be available during early boot,
a cpumem pointer and memory for the boot CPU may be statically
allocated.
.Pp
.Fn CPUMEM_BOOT_MEMORY
statically allocates memory for use on the boot CPU
before the other CPUs in the system have been attached.
The allocation is identified by
.Fa NAME ,
and provides the number of bytes specified by the
.Fa sz
argument.
The memory will be initialised to zeros.
.Pp
.Fn CPUMEM_BOOT_INITIALIZER
is used to initialise a cpumem pointer with the memory that was previously
allocated using
.Fn CPUMEM_BOOT_MEMORY
and identified by
.Fa NAME .
.Pp
.Fn cpumem_malloc_ncpus
allocates additional memory for the CPUs that were attached during boot.
The cpumem structure
.Fa cm
must have been initialised with
.Fn CPUMEM_BOOT_INITIALIZER .
The same number of bytes originally passed to
.Fa COUNTERS_BOOT_MEMORY
must be specified by
.Fa sz .
The
.Fa type
argument specifies the type of memory that the counters will be
allocated as via
.Xr malloc 9 .
The contents of the memory on the boot CPU will be preserved, while
the allocations for the additional CPU's will be zeroed on allocation.
.Pp
Per CPU memory that has been allocated with
.Fn CPUMEM_BOOT_MEMORY
and
.Fn cpumem_malloc_ncpus
cannot be deallocated with
.Fa cpumem_free .
Any attempt to do so will lead to undefined behaviour.
.Ss Per CPU Memory Access
.Fn cpumem_enter
provides access to the current CPU's memory allocation referenced by
.Fa cm .
.Pp
.Fn cpumem_leave
indicates the end of access to the current CPU's memory allocation referenced by
.Fa cm .
.Ss Per CPU Memory Iterators
.Fn cpumem_first
provides access to the first CPU's memory allocation referenced by
.Fa cm .
The iterator
.Fa ci
may be used in subsequent calls to
.Fn cpumem_next .
.Pp
.Fn cpumem_next
provides access to the next CPU's memory allocation referenced by
.Fa cm
and
.Fa ci .
.Pp
The
.Fn CPUMEM_FOREACH
macro iterates over each CPU's memory allocation referenced by
.Fa cm
using the iterator
.Fa ci ,
setting
.Fa VARNAME
to each CPU's allocation in turn.
.Sh CONTEXT
.Fn cpumem_get ,
.Fn cpumem_put ,
.Fn cpumem_malloc ,
.Fn cpumem_free ,
and
.Fn cpumem_malloc_ncpus
may be called during autoconf, or from process context.
.Pp
.Fn cpumem_enter ,
.Fn cpumem_leave ,
.Fn cpumem_first ,
.Fn cpumem_next ,
and
.Fn CPUMEM_FOREACH
may be called during autoconf, from process context, or from interrupt
context.
The per CPU memory API does not provide any locking or serialisation
of access to each CPU's memory allocation.
It is up to the caller to provide appropriate locking or serialisation
around calls to these functions to prevent concurrent access to the
relevant data structures.
.Sh RETURN VALUES
.Fn cpumem_get ,
.Fn cpumem_malloc ,
and
.Fn cpumem_malloc_ncpus
will return an opaque cpumem pointer that references each CPU's
memory allocation.
.Pp
.Fn cpumem_enter
returns a reference to the current CPU's memory allocation.
.Pp
.Fn cpumem_first
returns a reference to the first CPU's memory allocation.
.Pp
.Fn cpumem_next
returns a reference to the next CPU's memory allocation according to the
iterator
.Fa ci ,
or
.Dv NULL
if the iterator has run out of CPUs.
.Sh SEE ALSO
.Xr counters_alloc 9 ,
.Xr malloc 9 ,
.Xr pool_get 9
.Sh HISTORY
The per CPU memory API first appeared in
.Ox 6.1 .
.Sh AUTHORS
The per CPU memory API was written by
.An David Gwynne Aq Mt dlg@openbsd.org .