131 lines
4.6 KiB
Groff
131 lines
4.6 KiB
Groff
.\" $NetBSD: pcu.9,v 1.10 2014/05/25 14:56:23 rmind Exp $
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.\"
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.\" Copyright (c) 2012-2014 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 Mindaugas Rasiukevicius.
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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 25, 2014
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.Dt PCU 9
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.Os
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.Sh NAME
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.Nm pcu
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.Nd per-CPU unit (PCU)
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.Sh SYNOPSIS
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.In sys/pcu.h
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.Ft void
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.Fn pcu_load "const pcu_ops_t *pcu"
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.Ft void
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.Fn pcu_save "const pcu_ops_t *pcu"
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.Ft void
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.Fn pcu_save_all "lwp_t *l"
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.Ft void
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.Fn pcu_discard "const pcu_ops_t *pcu" "bool valid"
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.Ft void
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.Fn pcu_discard_all "lwp_t *l"
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.Ft bool
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.Fn pcu_valid_p "const pcu_ops_t *pcu"
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.\" -----
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.Sh DESCRIPTION
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Per CPU Unit (PCU) is an interface to manage synchronization of any
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per-CPU context (unit) tied to an LWP context.
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Typical use of PCU is for "lazy-switch" synchronization of the FPU state.
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Each PCU has its operations defined by a
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.Vt pcu_ops_t
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structure.
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Members of
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.Vt pcu_ops_t
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are
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.Bd -literal
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u_int pcu_id;
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void (*pcu_state_save)(lwp_t *l);
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void (*pcu_state_load)(lwp_t *l, u_int flags);
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void (*pcu_state_release)(lwp_t *l);
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.Ed
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.Pp
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.Bl -tag
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.It Fn pcu_state_save
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Indicate to MD code that the PCU state on the current CPU should be
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saved into the given LWP's MD storage.
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.It Fn pcu_state_load
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Load PCU state from the given LWP's MD storage to the current CPU.
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The
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.Ar flags
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argument is a combination of one or more of the following:
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.Bl -tag -width PCU_VALIDXXX
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.It Dv PCU_VALID
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Indicate that the PCU state is considered valid and need not be initialized.
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This is the case if the PCU state was already used (and thus loaded) by the LWP
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and has not been discarded since.
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.It Dv PCU_REENABLE
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Indicate that a fault reoccurred while the PCU state is loaded,
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therefore PCU should be re-enabled.
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This happens if LWP is context switched to another CPU and then switched
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back to the original CPU while the state on that CPU has not been changed
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by other LWPs.
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It may also happen due to instruction "bouncing" on some architectures.
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.El
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.It Fn pcu_state_release
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Indicate to MD code that the PCU ownership by the LWP was released,
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therefore the next use of PCU on the LWP shall be detected and
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.Fn pcu_load
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be called to reacquire the ownership.
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For example, this would normally be the changing of a bit for a CPU to
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trap on the execution of one of the PCU's instructions.
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.El
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.\" -----
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.Sh FUNCTIONS
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.Bl -tag -width pcu_save_allXXX
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.It Fn pcu_load
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Load or initialize the PCU state of the current LWP on the current CPU.
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.It Fn pcu_save
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Save the specified PCU state to the given LWP.
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.It Fn pcu_discard
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Discard the specified PCU state of the current LWP.
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The PCU state will be considered invalid,
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unless the "valid" parameter is set to true.
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.It Fn pcu_valid_p
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Return true if PCU state is considered valid.
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Generally, it always becomes "valid" when
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.Fn pcu_load
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is called by the LWP.
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Otherwise, return false.
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.It Fn pcu_discard_all
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Discard all PCU states of the given LWP; generally used by exec and exit.
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.It Fn pcu_save_all
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Save all PCU states of the given LWP; generally used during new LWP
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creation so that the PCU state of the parent could be copied.
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.El
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.\" -----
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.Sh CODE REFERENCES
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.Nm
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is implemented within the file
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.Pa sys/kern/subr_pcu.c .
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.Sh HISTORY
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PCU first appeared in
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.Nx 6.0 .
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.Sh AUTHORS
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.An Mindaugas Rasiukevicius Aq Mt rmind@NetBSD.org
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