206 lines
5.5 KiB
Groff
206 lines
5.5 KiB
Groff
.\"
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.\" Copyright (c) 1994, Henrik Vestergaard Draboel
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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 by Henrik Vestergaard Draboel.
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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 AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.Dd December 8, 2021
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.Dt RTPRIO 1
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.Os
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.Sh NAME
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.Nm rtprio ,
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.Nm idprio
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.Nd execute, examine or modify a utility's or process's realtime
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or idletime scheduling priority
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.Sh SYNOPSIS
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.Nm [id|rt]prio
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.Nm [id|rt]prio
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.Oo Fl Oc Ns Ar pid
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.Nm [id|rt]prio
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.Ar priority
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.Ar command
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.Op args
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.Nm [id|rt]prio
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.Ar priority
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.Fl Ar pid
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.Nm [id|rt]prio
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.Fl t
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.Ar command
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.Op args
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.Nm [id|rt]prio
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.Fl t
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.Fl Ar pid
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.Sh DESCRIPTION
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The
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.Nm
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utility is used for controlling realtime process scheduling.
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.Pp
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The
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.Nm idprio
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utility is used for controlling idletime process scheduling, and can be called
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with the same options as
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.Nm .
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.Pp
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A process with a realtime priority is not subject to priority
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degradation, and will only be preempted by another process of equal or
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higher realtime priority.
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.Pp
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A process with an idle priority will run only when no other
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process is runnable and then only if its idle priority is equal or
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greater than all other runnable idle priority processes.
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.Pp
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Both
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.Nm
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or
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.Nm idprio
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when called without arguments will return the realtime priority
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of the current process.
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.Pp
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If
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.Nm
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is called with 1 argument, it will return the realtime priority
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of the process with the specified
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.Ar pid .
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.Pp
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If
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.Ar priority
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is specified, the process or program is run at that realtime priority.
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If
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.Fl t
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is specified, the process or program is run as a normal (non-realtime)
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process.
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.Pp
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If
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.Ar -pid
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is specified, the process with the process identifier
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.Ar pid
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will be modified, else if
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.Ar command
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is specified, that program is run with its arguments.
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.Pp
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.Ar Priority
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is an integer between 0 and RTP_PRIO_MAX (usually 31).
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0 is the
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highest priority
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.Pp
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.Ar Pid
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of 0 means "the current process".
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.Pp
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Only root is allowed to set realtime or idle priority for a process.
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Exceptional privileges can be granted through the
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.Xr mac_priority 4
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policy and the realtime and idletime user groups.
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The
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.Xr sysctl 8
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variable
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.Va security.bsd.unprivileged_idprio
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is deprecated.
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If set to non-zero, it lets any user modify the idle priority of processes
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they own.
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.Pp
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Note that idle priority increases the chance that a deadlock can occur
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if a process locks a required resource and then does
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not get to run.
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.Sh EXIT STATUS
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If
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.Nm
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execute a command, the exit value is that of the command executed.
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In all other cases,
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.Nm
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exits 0 on success, and 1 for all other errors.
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.Sh EXAMPLES
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To see which realtime priority the current process is at:
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.Dl rtprio
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.Pp
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To see which realtime priority of process 1423:
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.Dl "rtprio 1423"
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.Pp
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To run
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.Xr cron 8
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at the lowest realtime priority:
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.Dl "rtprio 31 cron"
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.Pp
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To change the realtime priority of process 1423 to 16:
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.Dl "rtprio 16 -1423"
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.Pp
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To run
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.Xr tcpdump 1
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without realtime priority:
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.Dl "rtprio -t tcpdump"
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.Pp
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To change the realtime priority of process 1423
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to
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.Dv RTP_PRIO_NORMAL
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(non-realtime/normal priority):
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.Dl "rtprio -t -1423"
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.Pp
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To make depend while not disturbing other machine usage:
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.Dl "idprio 31 make depend"
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.Sh SEE ALSO
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.Xr nice 1 ,
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.Xr ps 1 ,
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.Xr rtprio 2 ,
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.Xr setpriority 2 ,
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.Xr nice 3 ,
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.Xr mac_priority 4 ,
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.Xr renice 8
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.Sh HISTORY
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The
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.Nm
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utility appeared in
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.Fx 2.0 ,
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but is similar to the HP-UX version.
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.Sh AUTHORS
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.An -nosplit
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.An Henrik Vestergaard Draboel Aq Mt hvd@terry.ping.dk
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is the original author.
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This
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implementation in
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.Fx
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was substantially rewritten by
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.An David Greenman .
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.Sh CAVEATS
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You can lock yourself out of the system by placing a cpu-heavy
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process in a realtime priority.
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.Sh BUGS
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There is no way to set/view the realtime priority of process 0
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(swapper) (see
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.Xr ps 1 ) .
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.Pp
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There is in
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.Fx
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no way to ensure that a process page is present in memory therefore
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the process may be stopped for pagein (see
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.Xr mprotect 2 ,
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.Xr madvise 2 ) .
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.Pp
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Under
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.Fx
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system calls are currently never preempted, therefore non-realtime
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processes can starve realtime processes, or idletime processes can
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starve normal priority processes.
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