Add pcu(9) man page.

share/man/man9/pcu.9

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+.\"	$NetBSD: pcu.9,v 1.1 2012/12/02 19:28:34 rmind Exp $
+.\"
+.\" Copyright (c) 2011 The NetBSD Foundation, Inc.
+.\" All rights reserved.
+.\"
+.\" This code is derived from software contributed to The NetBSD Foundation
+.\" by Mindaugas Rasiukevicius.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
+.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
+.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+.\" POSSIBILITY OF SUCH DAMAGE.
+.\"
+.Dd May 31, 2011
+.Dt PCU 9
+.Os
+.Sh NAME
+.Nm pcu
+.Nd per-CPU unit (PCU)
+.Sh SYNOPSIS
+.In sys/pcu.h
+.Ft void
+.Fn pcu_load "const pcu_ops_t *pcu"
+.Ft void
+.Fn pcu_save "const pcu_ops_t *pcu"
+.Ft void
+.Fn pcu_save_all "lwp_t *l"
+.Ft void
+.Fn pcu_discard "const pcu_ops_t *pcu"
+.Ft bool
+.Fn pcu_used_p "const pcu_ops_t *pcu"
+.\" -----
+.Sh DESCRIPTION
+Per CPU Unit (PCU) is an interface to manage synchronization of any
+per-CPU context (unit) tied to an LWP context.
+Typical use of PCU is for "lazy-switch" synchronisation of FPU state.
+Each PCU has its operations defined by a
+.Vt pcu_ops_t
+structure.
+Members of
+.Vt pcu_ops_t
+are
+.Bd -literal
+        u_int	pcu_id;
+        void	(*pcu_state_save)(lwp_t *l);
+        void	(*pcu_state_load)(lwp_t *l, bool used);
+        void	(*pcu_state_release)(lwp_t *l);
+.Ed
+.Pp
+.Bl -tag -width compact
+.It Fn pcu_state_save
+save the current CPU's state into the given LWP's MD storage.
+.It Fn pcu_state_load
+load PCU state from the given LWP's MD storage to the current CPU.
+The
+.Ar used
+argument is true if it is not the first time the LWP uses the PCU.
+.It Fn pcu_state_release
+indicate to MD code that the PCU ownership by the LWP was released,
+therefore the next use of PCU on the LWP shall be detected and
+.Fn pcu_load
+be called to reacquire ownership.
+For example, this would often be the changing of a bit for a CPU to
+trap on the execution of one of the PCU's instructions.
+.El
+.Sh FUNCTIONS
+.Bl -tag -width compact
+.It Fn pcu_load
+Load (initialize) the PCU state of the current LWP on the current CPU.
+.It Fn pcu_save
+Save the PCU state to the given LWP.
+.It Fn pcu_discard
+Discard the PCU state of the current LWP.
+.It Fn pcu_used_p
+Return true if PCU was used (i.e.
+.Fn pcu_load
+was called) by the LWP.
+Otherwise, return false.
+.Fn pcu_save_all
+save PCU state of the given LWP, so that it could be used later.
+.El
+.\" -----
+.Sh CODE REFERENCES
+.Nm
+is implemented within the file
+.Pa sys/kern/subr_pcu.c .
+.Sh HISTORY
+PCU first appeared in
+.Nx 6.0 .